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Poursharif S, Hamza S, Braam B. Changes in Proximal Tubular Reabsorption Modulate Microvascular Regulation via the TGF System. Int J Mol Sci 2022; 23:ijms231911203. [PMID: 36232506 PMCID: PMC9569689 DOI: 10.3390/ijms231911203] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2022] [Revised: 09/13/2022] [Accepted: 09/14/2022] [Indexed: 11/26/2022] Open
Abstract
This review paper considers the consequences of modulating tubular reabsorption proximal to the macula densa by sodium–glucose co-transporter 2 (SGLT2) inhibitors, acetazolamide, and furosemide in states of glomerular hyperfiltration. SGLT2 inhibitors improve renal function in early and advanced diabetic nephropathy by decreasing the glomerular filtration rate (GFR), presumably by activating the tubuloglomerular feedback (TGF) mechanism. Central in this paper is that the renoprotective effects of SGLT2 inhibitors in diabetic nephropathy can only be partially explained by TGF activation, and there are alternative explanations. The sustained activation of TGF leans on two prerequisites: no or only partial adaptation should occur in reabsorption proximal to macula densa, and no or only partial adaptation should occur in the TGF response. The main proximal tubular and loop of Henle sodium transporters are sodium–hydrogen exchanger 3 (NHE3), SGLT2, and the Na-K-2Cl co-transporter (NKCC2). SGLT2 inhibitors, acetazolamide, and furosemide are the most important compounds; inhibiting these transporters would decrease sodium reabsorption upstream of the macula densa and increase TGF activity. This could directly or indirectly affect TGF responsiveness, which could oppose sustained TGF activation. Only SGLT2 inhibitors can sustainably activate the TGF as there is only partial compensation in tubular reabsorption and TGF response. SGLT2 inhibitors have been shown to preserve GFR in both early and advanced diabetic nephropathy. Other than for early diabetic nephropathy, a solid physiological basis for these effects in advanced nephropathy is lacking. In addition, TGF has hardly been studied in humans, and therefore this role of TGF remains elusive. This review also considers alternative explanations for the renoprotective effects of SGLT2 inhibitors in diabetic patients such as the enhancement of microvascular network function. Furthermore, combination use of SGLT2 inhibitors and angiotensin-converting enzyme inhibitors (ACEi) or angiotensin receptor blockers (ARBs). in diabetes can decrease inflammatory pathways, improve renal oxygenation, and delay the progression of diabetic nephropathy.
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Affiliation(s)
- Shayan Poursharif
- Department of Medicine, Division of Nephrology and Immunology, University of Alberta, Edmonton, AB T6G 2G3, Canada
| | - Shereen Hamza
- Department of Physiology, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Branko Braam
- Department of Medicine, Division of Nephrology and Immunology, University of Alberta, Edmonton, AB T6G 2G3, Canada
- Department of Physiology, University of Alberta, Edmonton, AB T6G 2H7, Canada
- Correspondence: ; Tel.: +1-780-492-1867
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Feng W, Remedies CE, Obi IE, Aldous SR, Meera SI, Sanders PW, Inscho EW, Guan Z. Restoration of afferent arteriolar autoregulatory behavior in ischemia-reperfusion injury in rat kidneys. Am J Physiol Renal Physiol 2021; 320:F429-F441. [PMID: 33491564 PMCID: PMC7988813 DOI: 10.1152/ajprenal.00500.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 12/23/2020] [Accepted: 01/12/2021] [Indexed: 12/11/2022] Open
Abstract
Renal autoregulation is critical in maintaining stable renal blood flow (RBF) and glomerular filtration rate (GFR). Renal ischemia-reperfusion (IR)-induced kidney injury is characterized by reduced RBF and GFR. The mechanisms contributing to renal microvascular dysfunction in IR have not been fully determined. We hypothesized that increased reactive oxygen species (ROS) contributed to impaired renal autoregulatory capability in IR rats. Afferent arteriolar autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. IR was induced by 60 min of bilateral renal artery occlusion followed by 24 h of reperfusion. Afferent arterioles from sham rats exhibited normal autoregulatory behavior. Stepwise increases in perfusion pressure caused pressure-dependent vasoconstriction to 65 ± 3% of baseline diameter (13.2 ± 0.4 μm) at 170 mmHg. In contrast, pressure-mediated vasoconstriction was markedly attenuated in IR rats. Baseline diameter averaged 11.7 ± 0.5 µm and remained between 90% and 101% of baseline over 65-170 mmHg, indicating impaired autoregulatory function. Acute antioxidant administration (tempol or apocynin) to IR kidneys for 20 min increased baseline diameter and improved autoregulatory capability, such that the pressure-diameter profiles were indistinguishable from those of sham kidneys. Furthermore, the addition of polyethylene glycol superoxide dismutase or polyethylene glycol-catalase to the perfusate blood also restored afferent arteriolar autoregulatory responsiveness in IR rats, indicating the involvement of superoxide and/or hydrogen peroxide. IR elevated mRNA expression of NADPH oxidase subunits and monocyte chemoattractant protein-1 in renal tissue homogenates, and this was prevented by tempol pretreatment. These results suggest that ROS accumulation, likely involving superoxide and/or hydrogen peroxide, impairs renal autoregulation in IR rats in a reversible fashion.NEW & NOTEWORTHY Renal ischemia-reperfusion (IR) leads to renal microvascular dysfunction manifested by impaired afferent arteriolar autoregulatory efficiency. Acute administration of scavengers of reactive oxygen species, polyethylene glycol-superoxide dismutase, or polyethylene glycol-catalase following renal IR restored afferent arteriolar autoregulatory capability in IR rats, indicating that renal IR led to reversible impairment of afferent arteriolar autoregulatory capability. Intervention with antioxidant treatment following IR may improve outcomes in patients by preserving renovascular autoregulatory function and potentially preventing the progression to chronic kidney disease after acute kidney injury.
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Affiliation(s)
- Wenguang Feng
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Colton E Remedies
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Ijeoma E Obi
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Stephen R Aldous
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Samia I Meera
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Paul W Sanders
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
- Department of Veterans Affairs Medical Center, Birmingham, Alabama
| | - Edward W Inscho
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Zhengrong Guan
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
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Guan Z, Makled MN, Inscho EW. Purinoceptors, renal microvascular function and hypertension. Physiol Res 2020; 69:353-369. [PMID: 32301620 DOI: 10.33549/physiolres.934463] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Proper renal blood flow (RBF) and glomerular filtration rate (GFR) are critical for maintaining normal blood pressure, kidney function and water and electrolyte homeostasis. The renal microvasculature expresses a multitude of receptors mediating vasodilation and vasoconstriction, which can influence glomerular blood flow and capillary pressure. Despite this, RBF and GFR remain quite stable when arterial pressure fluctuates because of the autoregulatory mechanism. ATP and adenosine participate in autoregulatory control of RBF and GFR via activation of two different purinoceptor families (P1 and P2). Purinoceptors are widely expressed in renal microvasculature and tubules. Emerging data show altered purinoceptor signaling in hypertension-associated kidney injury, diabetic nephropathy, sepsis, ischemia-reperfusion induced acute kidney injury and polycystic kidney disease. In this brief review, we highlight recent studies and new insights on purinoceptors regulating renal microvascular function and renal hemodynamics. We also address the mechanisms underlying renal microvascular injury and impaired renal autoregulation, focusing on purinoceptor signaling and hypertension-induced renal microvascular dysfunction. Interested readers are directed to several excellent and comprehensive reviews that recently covered the topics of renal autoregulation, and nucleotides in kidney function under physiological and pathophysiological conditions (Inscho 2009, Navar et al. 2008, Carlstrom et al. 2015, Vallon et al. 2020).
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Affiliation(s)
- Z Guan
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, South Birmingham, USA.
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Vallon V, Unwin R, Inscho EW, Leipziger J, Kishore BK. Extracellular Nucleotides and P2 Receptors in Renal Function. Physiol Rev 2019; 100:211-269. [PMID: 31437091 DOI: 10.1152/physrev.00038.2018] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The understanding of the nucleotide/P2 receptor system in the regulation of renal hemodynamics and transport function has grown exponentially over the last 20 yr. This review attempts to integrate the available data while also identifying areas of missing information. First, the determinants of nucleotide concentrations in the interstitial and tubular fluids of the kidney are described, including mechanisms of cellular release of nucleotides and their extracellular breakdown. Then the renal cell membrane expression of P2X and P2Y receptors is discussed in the context of their effects on renal vascular and tubular functions. Attention is paid to effects on the cortical vasculature and intraglomerular structures, autoregulation of renal blood flow, tubuloglomerular feedback, and the control of medullary blood flow. The role of the nucleotide/P2 receptor system in the autocrine/paracrine regulation of sodium and fluid transport in the tubular and collecting duct system is outlined together with its role in integrative sodium and fluid homeostasis and blood pressure control. The final section summarizes the rapidly growing evidence indicating a prominent role of the extracellular nucleotide/P2 receptor system in the pathophysiology of the kidney and aims to identify potential therapeutic opportunities, including hypertension, lithium-induced nephropathy, polycystic kidney disease, and kidney inflammation. We are only beginning to unravel the distinct physiological and pathophysiological influences of the extracellular nucleotide/P2 receptor system and the associated therapeutic perspectives.
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Affiliation(s)
- Volker Vallon
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
| | - Robert Unwin
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
| | - Edward W Inscho
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
| | - Jens Leipziger
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
| | - Bellamkonda K Kishore
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
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Abstract
The myogenic response is a key autoregulatory mechanism in the mammalian kidney. Triggered by blood pressure perturbations, it is well established that the myogenic response is initiated in the renal afferent arteriole and mediated by alterations in muscle tone and vascular diameter that counterbalance hemodynamic perturbations. The entire process involves several subcellular, cellular, and vascular mechanisms whose interactions remain poorly understood. Here, we model and investigate the myogenic response of a multicellular segment of an afferent arteriole. Extending existing work, we focus on providing an accurate—but still computationally tractable—representation of the coupling among the involved levels. For individual muscle cells, we include detailed Ca2+ signaling, transmembrane transport of ions, kinetics of myosin light chain phosphorylation, and contraction mechanics. Intercellular interactions are mediated by gap junctions between muscle or endothelial cells. Additional interactions are mediated by hemodynamics. Simulations of time-independent pressure changes reveal regular vasoresponses throughout the model segment and stabilization of a physiological range of blood pressures (80–180 mmHg) in agreement with other modeling and experimental studies that assess steady autoregulation. Simulations of time-dependent perturbations reveal irregular vasoresponses and complex dynamics that may contribute to the complexity of dynamic autoregulation observed in vivo. The ability of the developed model to represent the myogenic response in a multiscale and realistic fashion, under feasible computational load, suggests that it can be incorporated as a key component into larger models of integrated renal hemodynamic regulation.
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Van Beusecum JP, Zhang S, Cook AK, Inscho EW. Acute toll-like receptor 4 activation impairs rat renal microvascular autoregulatory behaviour. Acta Physiol (Oxf) 2017; 221:204-220. [PMID: 28544543 DOI: 10.1111/apha.12899] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 12/16/2016] [Accepted: 05/18/2017] [Indexed: 12/24/2022]
Abstract
AIM Little is known about how toll-like receptor 4 (TLR4) influences the renal microvasculature. We hypothesized that acute TLR4 stimulation with lipopolysaccharide (LPS) impairs afferent arteriole autoregulatory behaviour, partially through reactive oxygen species (ROS). METHODS We assessed afferent arteriole autoregulatory behaviour after LPS treatment (1 mg kg-1 ; i.p.) using the in vitro blood-perfused juxtamedullary nephron preparation. Autoregulatory behaviour was assessed by measuring diameter responses to stepwise changes in renal perfusion pressure. TLR4 expression was assessed by immunofluorescence, immunohistochemistry and Western blot analysis in the renal cortex and vasculature. RESULTS Baseline arteriole diameter at 100 mmHg averaged 15.2 ± 1.2 μm and 12.2 ± 1.0 μm for control and LPS groups (P < 0.05) respectively. When perfusion pressure was increased in 15 mmHg increments from 65 to 170 mmHg, arteriole diameter in control kidneys decreased significantly to 69 ± 6% of baseline diameter. In the LPS-treated group, arteriole diameter remained essentially unchanged (103 ± 9% of baseline), indicating impaired autoregulatory behaviour. Pre-treatment with anti-TLR4 antibody or the TLR4 antagonist, LPS-RS, preserved autoregulatory behaviour during LPS treatment. P2 receptor reactivity was normal in control and LPS-treated rats. Pre-treatment with Losartan (angiotensin type 1 receptor blocker; (AT1 ) 2 mg kg-1 ; i.p.) increased baseline afferent arteriole diameter but did not preserve autoregulatory behaviour in LPS-treated rats. Acute exposure to Tempol (10-3 mol L-1 ), a superoxide dismutase mimetic, restored pressure-mediated vasoconstriction in kidneys from LPS-treated rats. CONCLUSION These data demonstrate that TLR4 activation impairs afferent arteriole autoregulatory behaviour, partially through ROS, but independently of P2 and AT1 receptor activation.
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Affiliation(s)
- J. P. Van Beusecum
- Division of Nephrology; Department of Medicine; University of Alabama at Birmingham; Birmingham AL USA
- Department of Physiology; Augusta University; Augusta GA USA
| | - S. Zhang
- Division of Nephrology; Department of Medicine; University of Alabama at Birmingham; Birmingham AL USA
- Department of Physiology; Augusta University; Augusta GA USA
| | - A. K. Cook
- Division of Nephrology; Department of Medicine; University of Alabama at Birmingham; Birmingham AL USA
- Department of Physiology; Augusta University; Augusta GA USA
| | - E. W. Inscho
- Division of Nephrology; Department of Medicine; University of Alabama at Birmingham; Birmingham AL USA
- Department of Physiology; Augusta University; Augusta GA USA
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Palant CE, Chawla LS, Faselis C, Li P, Pallone TL, Kimmel PL, Amdur RL. High serum creatinine nonlinearity: a renal vital sign? Am J Physiol Renal Physiol 2016; 311:F305-9. [PMID: 27194712 DOI: 10.1152/ajprenal.00025.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Accepted: 05/10/2016] [Indexed: 01/20/2023] Open
Abstract
Patients with chronic kidney disease (CKD) may have nonlinear serum creatinine concentration (SC) trajectories, especially as CKD progresses. Variability in SC is associated with renal failure and death. However, present methods for measuring SC variability are unsatisfactory because they blend information about SC slope and variance. We propose an improved method for defining and calculating a patient's SC slope and variance so that they are mathematically distinct, and we test these methods in a large sample of US veterans, examining the correlation of SC slope and SC nonlinearity (SCNL) and the association of SCNL with time to stage 4 CKD (CKD4) and death. We found a strong correlation between SCNL and rate of CKD progression, time to CKD4, and time to death, even in patients with normal renal function. We therefore argue that SCNL may be a measure of renal autoregulatory dysfunction that provides an early warning sign for CKD progression.
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Affiliation(s)
- Carlos E Palant
- Department of Medicine, Veterans Affairs Medical Center, Washington, District of Columbia; Division of Renal Diseases and Hypertension, Department of Medicine, George Washington University Medical Center, Washington, District of Columbia
| | - Lakhmir S Chawla
- Department of Medicine, Veterans Affairs Medical Center, Washington, District of Columbia; Division of Renal Diseases and Hypertension, Department of Medicine, George Washington University Medical Center, Washington, District of Columbia; Department of Anesthesiology and Critical Care Medicine, George Washington University Medical Center, Washington, District of Columbia
| | - Charles Faselis
- Department of Medicine, Veterans Affairs Medical Center, Washington, District of Columbia
| | - Ping Li
- Department of Medicine, Veterans Affairs Medical Center, Washington, District of Columbia; Division of Renal Diseases and Hypertension, Department of Medicine, George Washington University Medical Center, Washington, District of Columbia
| | - Thomas L Pallone
- Department of Medicine, University of Maryland at Baltimore, Baltimore, Maryland
| | - Paul L Kimmel
- Division of Renal Diseases and Hypertension, Department of Medicine, George Washington University Medical Center, Washington, District of Columbia; National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | - Richard L Amdur
- Department of Medicine, Veterans Affairs Medical Center, Washington, District of Columbia; Biostatistics Core, Veterans Affairs Medical Center, Washington, District of Columbia; Department of Surgery, George Washington University School of Medicine and Health Sciences, Washington, District of Columbia
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Abstract
Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.
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Affiliation(s)
- Mattias Carlström
- Department of Medicine, Division of Nephrology and Hypertension and Hypertension, Kidney and Vascular Research Center, Georgetown University, Washington, District of Columbia; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; and Department of Cell Biology and Physiology, UNC Kidney Center, and McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Christopher S Wilcox
- Department of Medicine, Division of Nephrology and Hypertension and Hypertension, Kidney and Vascular Research Center, Georgetown University, Washington, District of Columbia; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; and Department of Cell Biology and Physiology, UNC Kidney Center, and McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - William J Arendshorst
- Department of Medicine, Division of Nephrology and Hypertension and Hypertension, Kidney and Vascular Research Center, Georgetown University, Washington, District of Columbia; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; and Department of Cell Biology and Physiology, UNC Kidney Center, and McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
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Sorensen CM, Giese I, Braunstein TH, Brasen JC, Salomonsson M, Holstein-Rathlou NH. Role of connexin40 in the autoregulatory response of the afferent arteriole. Am J Physiol Renal Physiol 2012; 303:F855-63. [PMID: 22811484 DOI: 10.1152/ajprenal.00026.2012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Connexins in renal arterioles affect autoregulation of arteriolar tonus and renal blood flow and are believed to be involved in the transmission of the tubuloglomerular feedback (TGF) response across the cells of the juxtaglomerular apparatus. Connexin40 (Cx40) also plays a significant role in the regulation of renin secretion. We investigated the effect of deleting the Cx40 gene on autoregulation of afferent arteriolar diameter in response to acute changes in renal perfusion pressure. The experiments were performed using the isolated blood perfused juxtamedullary nephron preparation in kidneys obtained from wild-type or Cx40 knockout mice. Renal perfusion pressure was increased in steps from 75 to 155 mmHg, and the response in afferent arteriolar diameter was measured. Hereafter, a papillectomy was performed to inhibit TGF, and the pressure steps were repeated. Conduction of intercellular Ca(2+) changes in response to local electrical stimulation was examined in isolated interlobular arteries and afferent arterioles from wild-type or Cx40 knockout mice. Cx40 knockout mice had an impaired autoregulatory response to acute changes in renal perfusion pressure compared with wild-type mice. Inhibition of TGF by papillectomy significantly reduced autoregulation of afferent arteriolar diameter in wild-type mice. In Cx40 knockout mice, papillectomy did not affect the autoregulatory response, indicating that these mice have no functional TGF. Also, Cx40 knockout mice showed no conduction of intercellular Ca(2+) changes in response to local electrical stimulation of interlobular arteries, whereas the Ca(2+) response to norepinephrine was unaffected. These results suggest that Cx40 plays a significant role in the renal autoregulatory response of preglomerular resistance vessels.
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Affiliation(s)
- Charlotte Mehlin Sorensen
- Institute of Biomedical Sciences, Division of Renal and Vascular Physiology, University of Copenhagen, Denmark.
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Osmond DA, Inscho EW. P2X(1) receptor blockade inhibits whole kidney autoregulation of renal blood flow in vivo. Am J Physiol Renal Physiol 2010; 298:F1360-8. [PMID: 20335318 DOI: 10.1152/ajprenal.00016.2010] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In vitro experiments demonstrate that P2X(1) receptor activation is important for normal afferent arteriolar autoregulatory behavior, but direct in vivo evidence for this relationship occurring in the whole kidney is unavailable. Experiments were performed to test the hypothesis that P2X(1) receptors are important for autoregulation of whole kidney blood flow. Renal blood flow (RBF) was measured in anesthetized male Sprague-Dawley rats before and during P2 receptor blockade with PPADS, P2X(1) receptor blockade with IP5I, or A(1) receptor blockade with DPCPX. Both P2X(1) and A(1) receptor stimulation with alpha,beta-methylene ATP and CPA, respectively, caused dose-dependent decreases in RBF. Administration of either PPADS or IP5I significantly blocked P2X(1) receptor stimulation. Likewise, administration of DPCPX significantly blocked A(1) receptor activation to CPA. Autoregulatory behavior was assessed by measuring RBF responses to reductions in renal perfusion pressure. In vehicle-infused rats, as pressure was decreased from 120 to 100 mmHg, there was no decrease in RBF. However, in either PPADS- or IP5I-infused rats, each decrease in pressure resulted in a significant decrease in RBF, demonstrating loss of autoregulatory ability. In DPCPX-infused rats, reductions in pressure did not cause significant reductions in RBF over the pressure range of 100-120 mmHg, but the autoregulatory curve tended to be steeper than vehicle-infused rats over the range of 80-100 mmHg, suggesting that A(1) receptors may influence RBF at lower pressures. These findings are consistent with in vitro data from afferent arterioles and support the hypothesis that P2X(1) receptor activation is important for whole kidney autoregulation in vivo.
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Affiliation(s)
- David A Osmond
- Department of Physiology, Medical College of Georgia, Augusta, Georgia 30912, USA
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Lai EY, Onozato ML, Solis G, Aslam S, Welch WJ, Wilcox CS. Myogenic responses of mouse isolated perfused renal afferent arterioles: effects of salt intake and reduced renal mass. Hypertension 2010; 55:983-9. [PMID: 20194294 DOI: 10.1161/hypertensionaha.109.149120] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Because defects in renal autoregulation may contribute to renal barotrauma in chronic kidney disease, we tested the hypothesis that the myogenic response is diminished by reduced renal mass. Kidneys from 5/6 nephrectomized mice had only a minor increase in the glomerular sclerosis index. The telemetric mean arterial pressure (108+/-10 mm Hg) was unaffected after 3 months of high-salt intake (6% salt in chow) or reduced renal mass. Afferent arterioles from 5/6 nephrectomized mice and sham-operated controls were perfused ex vivo during step changes in pressure from 40 to 134 mm Hg. Afferent arterioles developed a constriction and a linear increase in active wall tension above a perfusion pressure of 36+/-6 mm Hg, without a plateau. The slope of active wall tension versus perfusion pressure defined the myogenic response, which was similar in sham mice fed normal or high-salt diets for 3 months (2.90+/-0.22 versus 3.22+/-0.40 dynes x cm(-1)/mm Hg; P value not significant). The myogenic response was unaffected after 3 days of reduced renal mass on either salt diet (3.39+/-0.61 versus 4.04+/-0.47 dynes x cm(-1)/mm Hg) but was reduced (P<0.05) in afferent arterioles from reduced renal mass groups fed normal and high salt at 3 months (2.10+/-0.28 and 1.35+/-0.21 dynes x cm(-1)/mm Hg). In conclusion, mouse renal afferent arterioles develop a linear increase in myogenic tone around the range of ambient perfusion pressures. This myogenic response is impaired substantially in the mouse model of prolonged reduced renal mass, especially during high salt intake.
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Affiliation(s)
- En Yin Lai
- Division of Nephrology and Hypertension, Georgetown University Medical Center, Washington, DC 20007, USA
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Inscho EW. ATP, P2 receptors and the renal microcirculation. Purinergic Signal 2009; 5:447-60. [PMID: 19294530 PMCID: PMC2776135 DOI: 10.1007/s11302-009-9147-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2007] [Accepted: 05/16/2008] [Indexed: 01/22/2023] Open
Abstract
Purinoceptors are rapidly becoming recognised as important regulators of tissue and organ function. Renal expression of P2 receptors is broad and diverse, as reflected by the fact that P2 receptors have been identified in virtually every major tubular/vascular element. While P2 receptor expression by these renal structures is recognised, the physiological functions that they serve remains to be clarified. Renal vascular P2 receptor expression is complex and poorly understood. Evidence suggests that different complements of P2 receptors are expressed by individual renal vascular segments. This unique distribution has given rise to the postulate that P2 receptors are important for renal vascular function, including regulation of preglomerular resistance and autoregulatory behaviour. More recent studies have also uncovered evidence that hypertension reduces renal vascular reactivity to P2 receptor stimulation in concert with compromised autoregulatory capability. This review will consolidate findings related to the role of P2 receptors in regulating renal microvascular function and will present areas of controversy related to the respective roles of ATP and adenosine in autoregulatory resistance adjustments.
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Affiliation(s)
- Edward W Inscho
- Department of Physiology, Medical College of Georgia, Augusta, Georgia,
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14
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Siu KL, Ahn JM, Chon KH. Electrohydraulic pump-driven closed-loop blood pressure-regulatory system. Am J Physiol Renal Physiol 2009; 296:F1530-6. [PMID: 19357178 DOI: 10.1152/ajprenal.90756.2008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In this paper, we describe our design for a new electrohydraulic (EH) pump-driven renal perfusion pressure (RPP)-regulatory system capable of implementing precise and rapid RPP regulation in experimental animals. Without this automated system, RPP is manually controlled via a blood pressure clamp, and the imprecision in this method leads to compromised RPP data. This motivated us to develop an EH pump-driven closed-loop blood pressure regulatory system based on flow-mediated occlusion using the vascular occlusive cuff technique. A closed-loop servo-controller system based on a proportional plus integral (PI) controller was designed using the dynamic feedback RPP signal from animals. In vivo performance was evaluated via flow-mediated RPP occlusion, maintenance, and release responses during baseline and ANG II-infused conditions. A step change of -30 mmHg, referenced to normal RPP, was applied to Sprague-Dawley rats with the proposed system to assess the performance of the PI controller. The PI's performance was compared against manual control of blood pressure clamp to regulate RPP. Rapid RPP occlusion (within 3 s) and a release time of approximately 0.3 s were obtained for the PI controller for both baseline and ANG II infusion conditions, in which the former condition was significantly better than manual control. We concluded that the proposed EH RPP-regulatory system could fulfill in vivo needs to study various pressure-flow relationships in diverse fields of physiology, in particular, studying the dynamics of the renal autoregulatory mechanisms.
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Affiliation(s)
- K L Siu
- Department of Biomedical Engineering, HSC T18, Rm. 030, SUNY Stony Brook, Stony Brook, NY 11794-8181, USA
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15
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Navar LG, Arendshorst WJ, Pallone TL, Inscho EW, Imig JD, Bell PD. The Renal Microcirculation. Compr Physiol 2008. [DOI: 10.1002/cphy.cp020413] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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16
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Navar LG, Arendshorst WJ, Pallone TL, Inscho EW, Imig JD, Bell PD. The Renal Microcirculation. Microcirculation 2008. [DOI: 10.1016/b978-0-12-374530-9.00015-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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17
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Wang X, Breaks J, Loutzenhiser K, Loutzenhiser R. Effects of inhibition of the Na+/K+/2Cl− cotransporter on myogenic and angiotensin II responses of the rat afferent arteriole. Am J Physiol Renal Physiol 2007; 292:F999-F1006. [PMID: 17090779 DOI: 10.1152/ajprenal.00343.2006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The Na+/K+/2Cl− cotransporter (NKCC) plays diverse roles in the kidney, contributing sodium reabsorption and tubuloglomerular feedback (TGF). However, NKCC is also expressed in smooth muscle and inhibitors of this transporter affect contractility in both vascular and nonvascular smooth muscle. In the present study, we investigated the effects of NKCC inhibitors on vasoconstrictor responses of the renal afferent arteriole using the in vitro perfused hydronephrotic rat kidney. This preparation has no tubules and no TGF, eliminating this potential complication. Furosemide and bumetanide inhibited myogenic responses in a concentration-dependent manner. Bumetanide was ∼20-fold more potent (IC50 1.0 vs. 20 μmol/l). At 100 and 10 μmol/l, furosemide and bumetanide inhibited myogenic responses by 72 ± 4 and 68 ± 5%, respectively. The maximal level of inhibition by bumetanide was not affected by nitric oxide synthase inhibition (100 μmol/l NG-nitro-l-arginine methyl ester). However, the time course for the dilation was slowed (from t1/2 = 4.0 ± 0.5 to 8.3 ± 1.7 min, P = 0.04), suggesting either a partial involvement of NO or a permissive effect of NO on relaxation kinetics. Bumetanide also inhibited ANG II-induced afferent arteriolar vasconstriction at similar concentrations. Finally, NKCC1, but not NKCC2, expression was demonstrated in the afferent arteriole by RT-PCR and the presence of NKCC1 in afferent arteriolar myocytes was confirmed by immunohistochemistry. In concert, these results indicate that NKCC modulation is capable of altering myogenic responses by a mechanism that does not involve TGF and suggest a potential role of NKCC1 in the regulation of vasomotor function in the renal microvasculature.
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Affiliation(s)
- Xuemei Wang
- Smooth Muscle Research Group, Department of Pharmacology and Therapeutics, University of Calgary Faculty of Medicine, Calgary, Alberta, Canada
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18
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Abstract
PURPOSE OF REVIEW Autoregulation of renal blood flow has traditionally been considered to stabilize glomerular filtration, and thus tubular load, in the face of blood pressure fluctuations. This view arose because of the contribution of tubuloglomerular feedback, which senses distal tubular fluid composition, to regulation and autoregulation of renal blood flow. Studies have indicated a more important role for the myogenic mechanism. It has been proposed that the 'purpose' of autoregulation is to defend glomerular structure. Both these views may be incomplete because neither takes into consideration the complex interactions between tubuloglomerular feedback and the myogenic mechanism and among nephrons whose afferent arterioles derived from a common interlobular artery. RECENT FINDINGS Recent findings indicate that it is now indisputable that effective autoregulation is necessary for defense of glomerular structure. Extensive modulation of the myogenic mechanism by tubuloglomerular feedback has been shown using a variety of experimental designs that have illuminated one pathway (neuronal nitric oxide synthase at the macula densa) by which this occurs. SUMMARY These findings indicate that the myogenic mechanism can no longer be considered as a purely vascular mechanism in the kidney and instead receives information via tubuloglomerular feedback about the status of renal function.
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Affiliation(s)
- William A Cupples
- Centre for Biomedical Research, Department of Biology, University of Victoria, Victoria, British Columbia, Canada.
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19
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Abstract
The kidney displays highly efficient autoregulation so that under steady-state conditions renal blood flow (RBF) is independent of blood pressure over a wide range of pressure. Autoregulation occurs in the preglomerular microcirculation and is mediated by two, perhaps three, mechanisms. The faster myogenic mechanism and the slower tubuloglomerular feedback contribute both directly and interactively to autoregulation of RBF and of glomerular capillary pressure. Multiple experiments have been used to study autoregulation and can be considered as variants of two basic designs. The first measures RBF after multiple stepwise changes in renal perfusion pressure to assess how a biological condition or experimental maneuver affects the overall pressure-flow relationship. The second uses time-series analysis to better understand the operation of multiple controllers operating in parallel on the same vascular smooth muscle. There are conceptual and experimental limitations to all current experimental designs so that no one design adequately describes autoregulation. In particular, it is clear that the efficiency of autoregulation varies with time and that most current techniques do not adequately address this issue. Also, the time-varying and nonadditive interaction between the myogenic mechanism and tubuloglomerular feedback underscores the difficulty of dissecting their contributions to autoregulation. We consider the modulation of autoregulation by nitric oxide and use it to illustrate the necessity for multiple experimental designs, often applied iteratively.
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Affiliation(s)
- William A Cupples
- Centre for Biomedical Research and Dept. of Biology, Univ. of Victoria, PO Box 3020, STN CSC, Victoria, BC, Canada.
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20
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Just A. Mechanisms of renal blood flow autoregulation: dynamics and contributions. Am J Physiol Regul Integr Comp Physiol 2006; 292:R1-17. [PMID: 16990493 DOI: 10.1152/ajpregu.00332.2006] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Autoregulation of renal blood flow (RBF) is caused by the myogenic response (MR), tubuloglomerular feedback (TGF), and a third regulatory mechanism that is independent of TGF but slower than MR. The underlying cause of the third regulatory mechanism remains unclear; possibilities include ATP, ANG II, or a slow component of MR. Other mechanisms, which, however, exert their action through modulation of MR and TGF are pressure-dependent change of proximal tubular reabsorption, resetting of RBF and TGF, as well as modulating influences of ANG II and nitric oxide (NO). MR requires < 10 s for completion in the kidney and normally follows first-order kinetics without rate-sensitive components. TGF takes 30-60 s and shows spontaneous oscillations at 0.025-0.033 Hz. The third regulatory component requires 30-60 s; changes in proximal tubular reabsorption develop over 5 min and more slowly for up to 30 min, while RBF and TGF resetting stretch out over 20-60 min. Due to these kinetic differences, the relative contribution of the autoregulatory mechanisms determines the amount and spectrum of pressure fluctuations reaching glomerular and postglomerular capillaries and thereby potentially impinge on filtration, reabsorption, medullary perfusion, and hypertensive renal damage. Under resting conditions, MR contributes approximately 50% to overall RBF autoregulation, TGF 35-50%, and the third mechanism < 15%. NO attenuates the strength, speed, and contribution of MR, whereas ANG II does not modify the balance of the autoregulatory mechanisms.
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Affiliation(s)
- Armin Just
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7545, USA.
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Loutzenhiser R, Griffin K, Williamson G, Bidani A. Renal autoregulation: new perspectives regarding the protective and regulatory roles of the underlying mechanisms. Am J Physiol Regul Integr Comp Physiol 2006; 290:R1153-67. [PMID: 16603656 PMCID: PMC1578723 DOI: 10.1152/ajpregu.00402.2005] [Citation(s) in RCA: 183] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
When the kidney is subjected to acute increases in blood pressure (BP), renal blood flow (RBF) and glomerular filtration rate (GFR) are observed to remain relatively constant. Two mechanisms, tubuloglomerular feedback (TGF) and the myogenic response, are thought to act in concert to achieve a precise moment-by-moment regulation of GFR and distal salt delivery. The current view is that this mechanism insulates renal excretory function from fluctuations in BP. Indeed, the concept that renal autoregulation is necessary for normal renal function and volume homeostasis has long been a cornerstone of renal physiology. This article presents a very different view, at least regarding the myogenic component of this response. We suggest that its primary purpose is to protect the kidney against the damaging effects of hypertension. The arguments advanced take into consideration the unique properties of the afferent arteriolar myogenic response that allow it to protect against the oscillating systolic pressure and the accruing evidence that when this response is impaired, the primary consequence is not a disturbed volume homeostasis but rather an increased susceptibility to hypertensive injury. It is suggested that redundant and compensatory mechanisms achieve volume regulation, despite considerable fluctuations in distal delivery, and the assumed moment-by-moment regulation of renal hemodynamics is questioned. Evidence is presented suggesting that additional mechanisms exist to maintain ambient levels of RBF and GFR within normal range, despite chronic alterations in BP and severely impaired acute responses to pressure. Finally, the implications of this new perspective on the divergent roles of the myogenic response to pressure vs. the TGF response to changes in distal delivery are considered, and it is proposed that in addition to TGF-induced vasoconstriction, vasodepressor responses to reduced distal delivery may play a critical role in modulating afferent arteriolar reactivity to integrate the regulatory and protective functions of the renal microvasculature.
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22
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Hashimoto S, Huang Y, Briggs J, Schnermann J. Reduced autoregulatory effectiveness in adenosine 1 receptor-deficient mice. Am J Physiol Renal Physiol 2005; 290:F888-91. [PMID: 16263804 DOI: 10.1152/ajprenal.00381.2005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Adjustments of renal vascular resistance in response to changes in blood pressure are mediated by an interplay between the myocyte-inherent myogenic and the kidney-specific tubuloglomerular feedback (TGF) mechanisms. Using mice with deletion of the A(1) adenosine receptor (A1AR) gene, we tested the prediction that the absence of TGF, previously established to result from A1AR deficiency, is associated with a reduction in the efficiency of autoregulation. In anesthetized wild-type (A1AR+/+) and A1AR-deficient mice (A1AR-/-), glomerular filtration rate (GFR) and renal blood flow (RBF) were determined before and after reducing renal perfusion pressure through a suprarenal aortic clamp. In response to a blood pressure reduction by 15.9 +/- 1.34 mmHg in A1AR-/- (n = 9) and by 14.2 +/- 0.9 mmHg in A1AR+/+ mice (n = 8; P = 0.31), GFR fell by 187.9 +/- 37 mul/min and by 72.3 +/- 10 mul/min in A1AR-/- and A1AR+/+ mice, respectively (P = 0.013). Similarly, with pressure reductions of 14.8 +/- 1.1 and 13.3 +/- 1.5 mmHg in A1AR-/- (n = 9) and wild-type mice (n = 8), respectively (P = 0.43), RBF fell by 0.17 +/- 0.02 ml/min in A1AR-/- mice and by only 0.08 +/- 0.02 ml/min in wild-type animals (P = 0.0039). Autoregulatory indexes for both GFR and RBF were significantly higher in A1AR-/- compared with A1AR+/+ mice, indicating reduced regulatory responsiveness in the knockout animals. We conclude that autoregulation of renal vascular resistance is less complete in A1AR-deficient mice, an effect that is presumably related to absence of TGF regulation in these animals.
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Affiliation(s)
- S Hashimoto
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
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23
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Marsh DJ, Sosnovtseva OV, Chon KH, Holstein-Rathlou NH. Nonlinear interactions in renal blood flow regulation. Am J Physiol Regul Integr Comp Physiol 2005; 288:R1143-59. [PMID: 15677526 DOI: 10.1152/ajpregu.00539.2004] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have developed a model of tubuloglomerular feedback (TGF) and the myogenic mechanism in afferent arterioles to understand how the two mechanisms are coupled. This paper presents the model. The tubular model predicts pressure, flow, and NaCl concentration as functions of time and tubular length in a compliant tubule that reabsorbs NaCl and water; boundary conditions are glomerular filtration rate (GFR), a nonlinear outflow resistance, and initial NaCl concentration. The glomerular model calculates GFR from a change in protein concentration using estimates of capillary hydrostatic pressure, tubular hydrostatic pressure, and plasma flow rate. The arteriolar model predicts fraction of open K channels, intracellular Ca concentration (Cai), potential difference, rate of actin–myosin cross bridge formation, force of contraction, and length of elastic elements, and was solved for two arteriolar segments, identical except for the strength of TGF input, with a third, fixed resistance segment representing prearteriolar vessels. The two arteriolar segments are electrically coupled. The arteriolar, glomerular, and tubular models are linked; TGF modulates arteriolar circumference, which determines vascular resistance and glomerular capillary pressure. The model couples TGF input to voltage-gated Ca channels. It predicts autoregulation of GFR and renal blood flow, matches experimental measures of tubular pressure and macula densa NaCl concentration, and predicts TGF-induced oscillations and a faster smaller vasomotor oscillation. There are nonlinear interactions between TGF and the myogenic mechanism, which include the modulation of the frequency and amplitude of the myogenic oscillation by TGF. The prediction of modulation is confirmed in a companion study ( 28 ).
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Affiliation(s)
- Donald J Marsh
- Dept. of Molecular Pharmacology, Physiology, & Biotechnology, Brown Univ., Biomedical Center B-5, Providence, RI 02912, USA.
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24
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Sansoè G, Silvano S, Mengozzi G, Smedile A, Touscoz G, Rosina F, Rizzetto M. Loss of tubuloglomerular feedback in decompensated liver cirrhosis: physiopathological implications. Dig Dis Sci 2005; 50:955-63. [PMID: 15906775 DOI: 10.1007/s10620-005-2671-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
In healthy subjects, arterial pressure reduction or renal ischemia produces renal artery dilatation through autoregulation and tubuloglomerular feedback (TuGF). Patients with decompensated cirrhosis have reduced kidney perfusion pressure but show renal vasoconstriction instead of autoregulation-mediated vasodilation. This study investigates the consequences of kidney autoregulation loss on renal perfusion, glomerular filtration rate, and tubular handling of electrolytes in both compensated and ascitic nonazotemic cirrhotic patients. Forty-two consecutive patients with diuretic-free liver cirrhosis (32 with preascitic and 10 with ascitic disease) and 10 controls were submitted to the following determinations: (a) basal plasma renin activity and aldosterone levels; (b) endogenous dopaminergic activity measured as incremental aldosterone responses during metoclopramide administration; and (c) renal clearances of sodium, potassium, inulin, para-aminohippurate and lithium. Compared with the other groups, ascitic patients showed lower renal plasma flow (P < 0.01) and lithium clearance (P < 0.05), a higher filtration fraction (P < 0.01), and secondary aldosteronism. Controls and preascitic patients displayed tubuloglomerular feedback (the mechanism increasing the glomerular filtration rate when a reduced sodium load reaches the distal tubule), as demonstrated by negative correlations between fractional excretion of lithium (an expression of fractional delivery of sodium to the distal nephron) and glomerular filtration rate (respectively, r = -0.73, P < 0.03, and r = -0.48, P < 0.01). Conversely, patients with ascites showed a positive correlation between lithium fractional excretion and glomerular filtration rate (r = 0.64, P < 0.05). Reduction in renal perfusion, increased filtration fraction, and TuGF derangement, as found in decompensated patients, are indicative of prevalent postglomerular arteriolar vasoconstriction, with ensuing stimulation of proximal tubular sodium reabsorption.
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25
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Ichai C, Giunti C. [On which renal haemodynamic and renal function parameters can we act to protect the kidney?]. ANNALES FRANCAISES D'ANESTHESIE ET DE REANIMATION 2005; 24:148-60. [PMID: 15737501 DOI: 10.1016/j.annfar.2004.12.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
Affiliation(s)
- C Ichai
- Département d'anesthésie-réanimation Est, service de réanimation CHU de Nice, hôpital Saint-Roch, 5, rue Pierre-Dévoluy, 06006 Nice cedex 1, France.
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26
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Abstract
Autoregulation of renal blood flow is an established physiological phenomenon, however the signalling mechanisms involved remain elusive. Autoregulatory adjustments in preglomerular resistance involve myogenic and tubuloglomerular feedback (TGF) influences. While there is general agreement on the participation of these two regulatory pathways, the signalling molecules and effector mechanisms have not been identified. Currently, there are two major hypotheses being considered to explain the mechanism by which TGF signals are transmitted from the macula densa to the afferent arteriole. The adenosine hypothesis proposes that the released adenosine triphosphate (ATP) is hydrolysed to adenosine and this product stimulates preglomerular vasoconstriction by activation of A(1) receptors on the afferent arteriole. Alternatively, the P2 receptor hypothesis postulates that ATP released from the macula densa directly stimulates afferent arteriolar vasoconstriction by activation of ATP-sensitive P2X(1) receptors. This hypothesis has emerged from the realization that P2X(1) receptors are heavily expressed along the preglomerular vasculature. Inactivation of P2X(1) receptors impairs autoregulatory responses while afferent arteriolar responses to A(1) adenosine receptor activation are retained. Autoregulatory behaviour is markedly attenuated in mice lacking P2X(1) receptors but responses to adenosine A(1) receptor activation remain intact. More recent experiments suggest that P2X(1) receptors play an essential role in TGF-dependent vasoconstriction of the afferent arteriole. Interruption of TGF-dependent influences on afferent arteriolar diameter, by papillectomy or furosemide treatment, significantly attenuated pressure-mediated afferent arteriolar vasoconstriction in wild-type mice but had no effect on the response in P2X(1) knockout mice. Collectively, these observations support an essential role for P2X(1) receptors in TGF-mediated afferent arteriolar vasoconstriction.
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Affiliation(s)
- E W Inscho
- Department of Physiology, Medical College of Georgia, Augusta, GA 30912-3000, USA
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27
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Inscho EW, Cook AK, Imig JD, Vial C, Evans RJ. Physiological role for P2X1 receptors in renal microvascular autoregulatory behavior. J Clin Invest 2004; 112:1895-905. [PMID: 14679185 PMCID: PMC296993 DOI: 10.1172/jci18499] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
This study tests the hypothesis that P2X1 receptors mediate pressure-induced afferent arteriolar autoregulatory responses. Afferent arterioles from rats and P2X1 KO mice were examined using the juxtamedullary nephron technique. Arteriolar diameter was measured in response to step increases in renal perfusion pressure (RPP). Autoregulatory adjustments in diameter were measured before and during P2X receptor blockade with NF279 or A1 receptor blockade with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). Acute papillectomy or furosemide perfusion was performed to interrupt distal tubular fluid flow past the macula densa, thus minimizing tubuloglomerular feedback-dependent influences on afferent arteriolar function. Under control conditions, arteriolar diameter decreased by 17% and 29% at RPP of 130 and 160 mmHg, respectively. Blockade of P2X1 receptors with NF279 blocked pressure-mediated vasoconstriction, reflecting an attenuated autoregulatory response. The A1 receptor blocker DPCPX did not alter autoregulatory behavior or the response to ATP. Deletion of P2X1 receptors in KO mice significantly blunted autoregulatory responses induced by an increase in RPP, and this response was not further impaired by papillectomy or furosemide. WT control mice exhibited typical RPP-dependent vasoconstriction that was significantly attenuated by papillectomy. These data provide compelling new evidence indicating that tubuloglomerular feedback signals are coupled to autoregulatory preglomerular vasoconstriction through ATP-mediated activation of P2X1 receptors.
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Affiliation(s)
- Edward W Inscho
- Department of Physiology, Medical College of Georgia, 1120 15th Street, Augusta, Georgia 30912-3000, USA.
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28
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Wronski T, Seeliger E, Persson PB, Forner C, Fichtner C, Scheller J, Flemming B. The step response: a method to characterize mechanisms of renal blood flow autoregulation. Am J Physiol Renal Physiol 2003; 285:F758-64. [PMID: 12851255 DOI: 10.1152/ajprenal.00420.2002] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Response of renal vasculature to changes in renal perfusion pressure (RPP) involves mechanisms with different frequency characteristics. Autoregulation of renal blood flow (RBF) is mediated by the rapid myogenic response, by the slower tubuloglomerular feedback (TGF) mechanism, and, possibly, by an even slower third mechanism. To evaluate the individual contribution of these mechanisms to RBF autoregulation, we analyzed the response of RBF to a step increase in RPP. In anesthetized rats, the suprarenal aorta was occluded for 30 s, and then the occlusion was released to induce a step increase in RPP. Three dampened oscillations were observed; their oscillation periods ranged from 9.5 to 13 s, from 34.2 to 38.6 s, and from 100.5 to 132.2 s, respectively. The two faster oscillations correspond with previously reported data on the myogenic mechanism and the TGF. In accordance, after furosemide, the amplitude of the intermediate oscillation was significantly reduced. Inhibition of nitric oxide synthesis by Nomega-nitro-l-arginine methyl ester significantly increased the amplitude of the 10-s oscillation. It is concluded that the parameters of the dampened oscillations induced by the step increase in RPP reflect properties of autoregulatory mechanisms. The oscillation period characterizes the individual mechanism, the dampening is a measure for the stability of the regulation, and the square of the amplitudes characterizes the power of the respective mechanism. In addition to the myogenic response and the TGF, a third rather slow mechanism of RBF autoregulation exists.
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Affiliation(s)
- T Wronski
- Johannes Müller Institut für Physiologie, Humboldt-Universität (Charité), Berlin, Germany.
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29
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Smith KM, Moore LC, Layton HE. Advective transport of nitric oxide in a mathematical model of the afferent arteriole. Am J Physiol Renal Physiol 2003; 284:F1080-96. [PMID: 12712988 DOI: 10.1152/ajprenal.00141.2002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endothelium-derived nitric oxide (NO) is thought to be short-lived in blood because of rapid removal from plasma, mainly by binding to Hb. The extent to which removal limits NO advection is unclear, especially for blood flow in the renal afferent arteriole (AA), which has a transit time of 3-30 ms. A mathematical model of AA fluid dynamics and myogenic response that includes NO diffusion, advection, degradation, and vasorelaxant action was used to estimate NO advective transport. Model simulations indicate that advective transport of locally produced NO is sufficient to yield physiologically significant NO concentrations along much of the AA. Advective transport is insensitive to NO scavenging by Hb because the NO-Hb binding rate is slow relative to AA transit time. Hence, plasma NO concentration near the vessel wall is influenced by both diffusion from endothelial cells and advection from upstream sites. Simulations also suggest that NO advection may constitute a mechanism to stabilize arteriolar flow in response to a localized vasoconstriction accompanied by enhanced NO release.
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Affiliation(s)
- Kayne M Smith
- Department of Mathematics, Suke University , Durham, North Carolina 27708-0320, USA
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30
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Affiliation(s)
- Simon T Kudnig
- Department of Clinical Sciences, Colorado State University, Fort Collins 80525, USA
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31
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Kiil F. Analysis of the tubuloglomerular feedback mechanism in renal autoregulation. ACTA PHYSIOLOGICA SCANDINAVICA 2002; 174:357-66. [PMID: 11942923 DOI: 10.1046/j.1365-201x.2002.00969.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Along the juxtaglomerular segment of the afferent arteriole the luminal pressure p approaches the glomerular capillary pressure of 55-60 mmHg. At such low luminal pressures the myogenic mechanism contracts only if extravascular pressure p(ex) is subatmospheric. According to Poiseuille's formula complete autoregulation requires that blood flow is F=5Kr(0)(4)/Deltax at arterial pressures exceeding 65 mmHg; r(0) is the radius of the relaxed segment at transmural pressure p - p(ex) < or =60 mmHg, where p(ex) is the extravascular pressure; Deltax is the length of the main preglomerular segment, 10 times longer than the juxtaglomerular segment. Consistent with in vitro studies a myogenic mechanism may reduce the relaxed juxtaglomerular radius r(jx)=0.7r(0) by 40% at a transmural pressure of 140 mmHg. Fifty and 60% reductions are also considered. Integration of Poiseuille's formula shows that complete autoregulation of preglomerular blood flow requires negative extravascular pressures p(ex)= -90 to -55 mmHg dependent on contractile force. Negative pressure of this magnitude is generated by effective hyperosmolality <5 mOsm across the membrane separating cleft from pole cushion. Negative pressure stays constant at arterial pressures exceeding 90-110 mmHg, implying constant tubuloglomerular feedback, but approaches atmospheric pressure at lower arterial pressure, suggesting maintenance of blood flow by reduction in the glomerular filtration rate; a rise in macula densa concentrations [NaCl](md) by 0.15 mM or [NaHCO(3)](md) by 2 mM raises extravascular pressure towards atmospheric levels by approximately 40 mmHg. A 40-mmHg rise in interstitial pressure exerts the same effect. Loop diuretics nullify osmotic force and dilate juxtaglomerular and main segments by raising juxtaglomerular extravascular pressure towards atmospheric levels.
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Affiliation(s)
- F Kiil
- Institute for Experimental Medical Research, University of Oslo, Ullevål University Hospital, Kirkeveien 166, N-0407 Oslo 4, Norway
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Brown R, Ollerstam A, Johansson B, Skøtt O, Gebre-Medhin S, Fredholm B, Persson AE. Abolished tubuloglomerular feedback and increased plasma renin in adenosine A1 receptor-deficient mice. Am J Physiol Regul Integr Comp Physiol 2001; 281:R1362-7. [PMID: 11641103 DOI: 10.1152/ajpregu.2001.281.5.r1362] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The hypothesis that adenosine acting on adenosine A1 receptors (A1R) regulates several renal functions and mediates tubuloglomerular feedback (TGF) was examined using A1R knockout mice. We anesthetized knockout, wild-type, and heterozygous mice and measured glomerular filtration rate, TGF response using the stop-flow pressure (P(sf)) technique, and plasma renin concentration. The A1R knockout mice had an increased blood pressure compared with wild-type and heterozygote mice. Glomerular filtration rate was similar in all genotypes. Proximal tubular P(sf) was decreased from 36.7 +/- 1.2 to 25.3 +/- 1.6 mmHg in the A1R+/+ mice and from 38.1 +/- 1.0 to 27.4 +/- 1.1 mmHg in A1R+/- mice in response to an increase in tubular flow rate from 0 to 35 nl/min. This response was abolished in the homozygous A1R-/- mice (from 39.1 +/- 4.1 to 39.2 +/- 4.5 mmHg). Plasma renin activity was significantly greater in the A1R knockout mice [74.2 +/- 14.3 milli-Goldblatt units (mGU)/ml] mice compared with the wild-type and A1R+/- mice (36.3 +/- 8.5 and 34.1 +/- 9.6 mGU/ml), respectively. The results demonstrate that adenosine acting on A1R is required for TGF and modulates renin release.
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Affiliation(s)
- R Brown
- Department of Medical Cell Biology, Division of Integrative Physiology, Uppsala University, S-751 23 Uppsala, Sweden
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Wåhlin N, Stenberg A, Persson AE. Effect of thromboxane and nitric oxide blockade on renal blood flow increase during volume expansion in hydronephrotic rats. SCANDINAVIAN JOURNAL OF UROLOGY AND NEPHROLOGY 2001; 35:84-91. [PMID: 11411664 DOI: 10.1080/003655901750170362] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
OBJECTIVE It has recently been found that hydronephrotic rats, despite low diuresis, show a significant increase in renal blood flow (RBF) during volume expansion. The present experiments were designed to evaluate the mechanisms underlying this phenomenon. MATERIAL AND METHODS Three-week-old Sprague-Dawley rats underwent partial obstruction of the left ureter using the Ulm-Miller psoas groove technique. The effects on RBF were studied 3 weeks later under general anesthesia using real-time ultrasound flowmetry, first during normohydration and then during extracellular volume expansion, in both untreated animals, and after prior blockade of either thromboxane or nitric oxide. RESULTS Significant hydronephrosis developed in all cases. RBF was normal under control conditions. During volume expansion RBF increased significantly in untreated experimental animals (mean 7.5%). In contrast to this finding, RBF remained unchanged during volume expansion in both the thromboxane and nitric oxide blockade groups. CONCLUSION It is concluded that a thromboxane- and/or nitric oxide-dependent RBF redistribution takes place in hydronephrotic kidneys during volume expansion.
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Affiliation(s)
- N Wåhlin
- Department of Pediatric Surgery, University Children's Hospital, Uppsala, Sweden.
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Nishiyama A, Majid DS, Walker M, Miyatake A, Navar LG. Renal interstitial atp responses to changes in arterial pressure during alterations in tubuloglomerular feedback activity. Hypertension 2001; 37:753-9. [PMID: 11230369 DOI: 10.1161/01.hyp.37.2.753] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We recently demonstrated a direct relationship between autoregulation-related changes in renal vascular resistance (RVR) and renal interstitial ATP concentrations. To assess the possible role for extracellular ATP in the regulation of tubuloglomerular feedback (TGF)-mediated autoregulatory adjustments in RVR, renal interstitial ATP concentrations were measured with microdialysis probes in anesthetized dogs at different renal arterial pressures (RAPs) within the autoregulatory range during augmented and diminished activity of the TGF mechanism. Stepwise reductions in RAP from ambient pressure (129+/-3 mm Hg) to 102+/-2 mm Hg (step 1) and 75+/-1 mm Hg (step 2) resulted in significant decreases in ATP concentrations from 9.0+/-0.8 to 6.3+/-0.6 nmol/L in step 1 and to 4.2+/-0.5 nmol/L in step 2. Changes in RVR were highly correlated with changes in ATP concentrations (r=0.86, P<0.001, n=12). Acetazolamide (100 microgram. kg(-1). min(-1), n=6), which increases solute delivery to the macula densa, thus augmenting TGF activity, significantly decreased renal blood flow (RBF) by -16+/-2% and glomerular filtration rate (GFR) by -22+/-4% and increased ATP concentrations from 8.4+/-0.7 to 15.5+/-1.4 nmol/L. Although basal RBF and GFR levels were reduced by the acetazolamide infusion, autoregulation efficiency was maintained, and interstitial ATP concentrations were significantly decreased in response to reductions in RAP by -36+/-4% in step 1 and by -54+/-2% in step 2. The relationship between changes in RVR and interstitial ATP concentrations was preserved during acetazolamide treatment (r=0.80, P<0.01). Inhibition of the TGF mechanism by furosemide significantly increased RBF by 33+/-6% and GFR by 13+/-2% and decreased ATP concentrations from 8.9+/-1.4 to 5.0+/-0.8 nmol/L (n=6). Furosemide caused marked impairment of RBF and GFR autoregulatory efficiency (by -14+/-3% and -11+/-3% in step 1 and by -26+/-2% and -18+/-4% in step 2, respectively). In the furosemide-treated kidneys, interstitial ATP levels remained low and were not altered during reductions in RAP (4.7+/-0.7 nmol/L in step 1 and 4.7+/-0.8 nmol/L in step 2), and changes in RVR did not exhibit a correlation with changes in ATP concentrations (r=0.22, P=0.30). These data support the hypothesis that extracellular ATP contributes to autoregulatory adjustments in RVR that are mediated by changes in activity of the TGF mechanism.
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Affiliation(s)
- A Nishiyama
- Department of Physiology, Tulane University Health Sciences Center, New Orleans, LA, USA.
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Walker M, Harrison-Bernard LM, Cook AK, Navar LG. Dynamic interaction between myogenic and TGF mechanisms in afferent arteriolar blood flow autoregulation. Am J Physiol Renal Physiol 2000; 279:F858-65. [PMID: 11053046 DOI: 10.1152/ajprenal.2000.279.5.f858] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The dynamic activity of afferent arteriolar diameter (AAD) and blood flow (AABF) responses to a rapid step increase in renal arterial pressure (100-148 mmHg) was examined in the kidneys of normal Sprague-Dawley rats (n = 11) before [tubuloglomerular feedback (TGF)-intact] and after interruption of distal tubular flow (TGF-independent). Utilizing the in vitro blood-perfused juxtamedullary nephron preparation, fluctuations in AAD and erythrocyte velocity were sampled by using analog-to-digital computerized conversion, video microscopy, image shearing, and fast-frame, slow-frame techniques. These assessments enabled dynamic characterization of the autonomous actions and collective interactions between the myogenic and TGF mechanisms at the level of the afferent arteriole. The TGF-intact and TGF-independent systems exhibited common initial (0-24 vs. 0-13 s, respectively) response slope kinetics (-0.53 vs. -0.47% DeltaAAD/s; respectively) yet different maximum vasoconstrictive magnitude (-11.28 +/- 0.1 vs. -7. 02 +/- 0.9% DeltaAAD; P < 0.05, respectively). The initial AABF responses similarly exhibited similar kinetics but differing magnitudes. In contrast, during the sustained pressure input (13-97 s), the maximum vasoconstrictor magnitude (-7.02 +/- 0.9% DeltaAAD) and kinetics (-0.01% DeltaAAD/s) of the TGF-independent system were markedly blunted whereas the TGF-intact system exhibited continued vasoconstriction with slower kinetics (-0.20% DeltaAAD/s) until a steady-state plateau was reached (-25.9 +/- 0.4% DeltaAAD). Thus the TGF mechanism plays a role in both direct mediation of vasoconstriction and in modulation of the myogenic response.
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Affiliation(s)
- M Walker
- Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA.
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Layton HE, Pitman EB, Moore LC. Limit-cycle oscillations and tubuloglomerular feedback regulation of distal sodium delivery. Am J Physiol Renal Physiol 2000; 278:F287-301. [PMID: 10662733 DOI: 10.1152/ajprenal.2000.278.2.f287] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A mathematical model was used to evaluate the potential effects of limit-cycle oscillations (LCO) on tubuloglomerular feedback (TGF) regulation of fluid and sodium delivery to the distal tubule. In accordance with linear systems theory, simulations of steady-state responses to infinitesimal perturbations in single-nephron glomerular filtration rate (SNGFR) show that TGF regulatory ability (assessed as TGF compensation) increases with TGF gain magnitude gamma when gamma is less than the critical value gamma(c), the value at which LCO emerge in tubular fluid flow and NaCl concentration at the macula densa. When gamma > gamma(c) and LCO are present, TGF compensation is reduced for both infinitesimal and finite perturbations in SNGFR, relative to the compensation that could be achieved in the absence of LCO. Maximal TGF compensation occurs when gamma approximately gamma(c). Even in the absence of perturbations, LCO increase time-averaged sodium delivery to the distal tubule, while fluid delivery is little changed. These effects of LCO are consequences of nonlinear elements in the TGF system. Because increased distal sodium delivery may increase the rate of sodium excretion, these simulations suggest that LCO enhance sodium excretion.
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Affiliation(s)
- H E Layton
- Department of Mathematics, Duke University, Durham, North Carolina 27708-0320, USA.
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Ichihara A, Imig JD, Navar LG. Cyclooxygenase-2 modulates afferent arteriolar responses to increases in pressure. Hypertension 1999; 34:843-7. [PMID: 10523371 DOI: 10.1161/01.hyp.34.4.843] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This study was designed to examine the contribution of cyclooxygenase-2 (COX-2) in the afferent arteriolar autoregulatory responses to increases in perfusion pressure and its relationship with neuronal nitric oxide synthase (nNOS). In rat kidneys, afferent arteriolar diameter responses to increases in perfusion pressure were assessed in vitro with the blood-perfused juxtamedullary nephron technique. Basal afferent arteriolar diameter at 100 mm Hg averaged 21.0+/-1.2 microm (n=7), and the vasoconstrictor response to increasing perfusion pressure to 160 mm Hg averaged 18.4+/-1.2%. Superfusion with the COX-2 inhibitor NS398 (10 micromol/L) did not influence basal diameters, but it did significantly enhance the vasoconstrictor response to the increase in perfusion pressure (32.9+/-4.0%). In contrast to previous findings that the nNOS inhibitor S-methyl-L-thiocitrulline (10 micromol/L) enhanced afferent arteriolar autoregulatory responses in normal rat kidneys, in this study, administration of 10 micromol/L S-methyl-L-thiocitrulline did not further modulate the vasoconstrictor response to increases in perfusion pressure in the NS398-treated kidneys of normal rats (31.8+/-4.7%). When tubuloglomerular feedback activity was interrupted by papillectomy and the addition of 50 micromol/L furosemide to the blood perfusate (n=5 for each), the afferent arteriolar constrictor responses to increasing perfusion pressure to 160 mm Hg averaged 7.9+/-0.9% and 10.7+/-0.7%, respectively, and they were significantly attenuated compared with the responses observed in control kidneys. NS398 treatment did not modulate the afferent arteriolar autoregulatory responses in papillectomized or furosemide-treated kidneys. These results indicate that COX-2-derived metabolites contribute to the nNOS modulation of pressure-mediated afferent arteriolar autoregulatory responses.
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Affiliation(s)
- A Ichihara
- Department of Physiology, Tulane University School of Medicine, New Orleans, LA, USA
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Ichihara A, Navar LG. Neuronal NOS contributes to biphasic autoregulatory response during enhanced TGF activity. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:F113-20. [PMID: 10409304 DOI: 10.1152/ajprenal.1999.277.1.f113] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To assess the afferent arteriolar autoregulatory response during increased activity of the tubuloglomerular feedback (TGF) mechanism and to delineate the contribution of neuronal nitric oxide synthase (nNOS) to this response, afferent arteriolar diameter responses to changes in renal perfusion pressure (RPP) were monitored in vitro using the blood-perfused rat juxtamedullary nephron preparation. At RPP of 100 mmHg, basal afferent arteriolar diameter averaged 21.1 +/- 1.4 micrometer (n = 9). The initial and sustained constrictor responses of afferent arterioles to a 60-mmHg increase in RPP averaged 14.8 +/- 1.4% and 13.3 +/- 1.3%, respectively. Acetazolamide treatment, which enhances TGF responsiveness by increasing distal nephron volume delivery, significantly decreased basal afferent arteriolar diameter by 8.2 +/- 0.5% and enhanced the initial response (25.5 +/- 2.3%) to a 60-mmHg increase in RPP but did not alter the sustained response (14.3 +/- 1.5%). In another series of experiments, nNOS inhibition with 10 microM S-methyl-L-thiocitrulline (L-SMTC) significantly decreased afferent arteriolar diameter from 20.3 +/- 1.3 to 18.3 +/- 1.1 micrometer (n = 7) and enhanced both the initial (34.4 +/- 3.5%) and sustained constrictor responses (27.6 +/- 2.9%) to a 60-mmHg increase in RPP. Treatment with acetazolamide further enhanced both initial (56.4 +/- 3.0%) and sustained responses (54.6 +/- 2.7%). Interruption of distal delivery by transection of the loops of Henle prevented the enhanced responses to increases in RPP elicited with either acetazolamide or L-SMTC. These results indicate that nNOS contributes to the counteracting resetting process of biphasic afferent arteriolar constrictor responses to increases in RPP through a TGF-dependent mechanism.
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Affiliation(s)
- A Ichihara
- Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
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Berthold H, Münter K, Just A, Kirchheim HR, Ehmke H. Contribution of endothelin to renal vascular tone and autoregulation in the conscious dog. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:F417-24. [PMID: 10070165 DOI: 10.1152/ajprenal.1999.276.3.f417] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Exogenous endothelin-1 (ET-1) is a strong vasoconstrictor in the canine kidney and causes a decrease in renal blood flow (RBF) by stimulating the ETA receptor subtype. The aim of the present study was to investigate the role of endogenously generated ET-1 in renal hemodynamics under physiological conditions. In six conscious foxhounds, the time course of the effects of the selective ETA receptor antagonist LU-135252 (10 mg/kg iv) on mean arterial blood pressure (MAP), heart rate (HR), RBF, and glomerular filtration rate (GFR), as well as its effects on renal autoregulation, were examined. LU-135252 increased RBF by 20% (from 270 +/- 21 to 323 +/- 41 ml/min, P < 0.05) and HR from 76 +/- 5 to 97 +/- 8 beats/min (P < 0. 05), but did not alter MAP, GFR, or autoregulation of RBF and GFR. Since a number of interactions between ET-1 and the renin-angiotensin system have been reported previously, experiments were repeated during angiotensin converting enzyme (ACE) inhibition by trandolaprilat (2 mg/kg iv). When ETA receptor blockade was combined with ACE inhibition, which by itself had no effects on renal hemodynamics, marked changes were observed: MAP decreased from 91 +/- 4 to 80 +/- 5 mmHg (P < 0.05), HR increased from 85 +/- 5 to 102 +/- 11 beats/min (P < 0.05), and RBF increased from 278 +/- 23 to 412 +/- 45 ml/min (P < 0.05). Despite a pronounced decrease in renal vascular resistance over the entire pressure range investigated (40-100 mmHg), the capacity of the kidneys to autoregulate RBF was not impaired. The GFR remained completely unaffected at all pressure levels. These results demonstrate that endogenously generated ET-1 contributes significantly to renal vascular tone but does not interfere with the mechanisms of renal autoregulation. If ETA receptors are blocked, then the vasoconstrictor effects of ET-1 in the kidney are compensated for to a large extent by an augmented influence of ANG II. Thus ET-1 and ANG II appear to constitute a major interrelated vasoconstrictor system in the control of RBF.
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Affiliation(s)
- H Berthold
- I. Physiologisches Institut der Ruprecht-Karls-Universität Heidelberg, 69120 Heidelberg, Germany
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Cupples WA, Loutzenhiser RD. Dynamic autoregulation in the in vitro perfused hydronephrotic rat kidney. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:F126-30. [PMID: 9689014 DOI: 10.1152/ajprenal.1998.275.1.f126] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Renal autoregulation is mediated by tubuloglomerular feedback, operating at 0.03-0.05 Hz, and a faster system, operating at 0.1-0.2 Hz, that has been attributed by exclusion to myogenic vasoconstriction. In this study, we examined dynamic autoregulation in the hydronephrotic rat kidney, which lacks tubuloglomerular feedback but exhibits pressure-induced afferent arteriolar vasoconstriction. Kidneys were harvested under anesthesia from Sprague-Dawley rats and perfused in vitro using defined, colloid-free medium. Renal perfusate flow was assessed during forced pressure fluctuations at mean pressures of 60-140 mmHg. Transfer function analysis revealed passive behavior at 60 mmHg and active, pressure-dependent responses at higher pressures. In all cases, coherence was high (0.89 +/- 0.03 between 0.01 and 0.9 Hz). There was a resonance peak in admittance gain at approximately 0.3 Hz and an associated broad peak in phase angle. Below this frequency, gain declined progressively. The minimum gain achieved at 0.01-0.05 Hz was pressure sensitive, being 1.08 +/- 0.02 at 60 mmHg and 0.71 +/- 0.04 at 140 mmHg. These findings are consistent with in vivo results and with model-based predictions of the dynamics of myogenic autoregulation, supporting the postulate that the rapid component of autoregulation reflects operation of a myogenic mechanism.
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Affiliation(s)
- W A Cupples
- Division of Nephrology and Lady Davis Institute, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada
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Nafz B, Ehmke H, Wagner CD, Kirchheim HR, Persson PB. Blood pressure variability and urine flow in the conscious dog. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:F680-6. [PMID: 9575891 DOI: 10.1152/ajprenal.1998.274.4.f680] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Pressure-dependent urine production is considered to be a major factor in long-term blood pressure control. The phenomenon has been well characterized for fixed levels of renal perfusion pressure (RPP), but the influence of physiological fluctuations in RPP and spontaneous variations in renal blood flow (RBF) on short-term urine flow (UV) remain unclear. To clarify this issue, we studied the interdependence of RPP, RBF, and UV in 13 conscious foxhounds during a single-step pressure reduction, under normal conditions, and with induced pressure changes. Reducing RPP in a single step to approximately 80 mmHg revealed short response times of RBF (0.4 +/- 0.1 s, n = 7) as well as of UV (8.1 +/- 0.8 s, n = 7). Under control conditions, UV was coupled with spontaneous variations of RBF (r = 0.94, P < 0.001), in contrast to RPP, which showed no significant correlation with UV (r = 0.09, P = NS). To discern the pressure and blood flow dependency of UV at a reduced RPP, we induced 0.9-mHz blood pressure oscillations (80 +/- 10 mmHg), which phase shifted RPP and RBF. Conversely, under these conditions, UV was dependent on RPP (r = 0.95, P < 0.001). These results suggest that spontaneous fluctuations in RBF around a normal baseline level lead to concomitant changes in urine production, in contrast to physiological short-term oscillations in RPP, which are not correlated to changes in UV. However, during induced oscillations of perfusion pressure, the blood flow dependence was no longer observed and UV was entirely pressure dependent.
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Affiliation(s)
- B Nafz
- Institut für Physiologie der Charité, Humboldt Universität zu Berlin, Germany
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Tönshoff B, Kaskel FJ, Moore LC. Effects of insulin-like growth factor I on the renal juxtamedullary microvasculature. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:F120-8. [PMID: 9458831 DOI: 10.1152/ajprenal.1998.274.1.f120] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
To characterize the effects on the rat renal preglomerular microvasculature of insulin-like growth factor I (IGF-I), experiments were performed using the in vitro blood-perfused juxtamedullary nephron preparation. IGF-I induced a reversible vasodilation of pre- but not postglomerular microvessels in a dose-dependent manner (10(-9)-10(-7) M). The IGF-I-induced vasodilation was similar in all preglomerular vascular segments: interlobular artery, 11.5 +/- 1.2% of control (n = 16); mid-afferent arterioles, 11.6 +/- 1.7% (n = 24); and juxtaglomerular afferent segments, 16.1 +/- 2.8% (n = 19). Renal autoregulatory capacity was not reduced by IGF-I. Pretreatment with the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (10(-4) M) completely inhibited the vasodilatory response to IGF-I. IGF-I induced a rapid increase of NO concentration in intact renal microvessels, monitored by a NO-selective voltametric microelectrode. Pretreatment with the cyclooxygenase inhibitor indomethacin (10(-5) M) not only abrogated the IGF-I-induced dilation, but, moreover, IGF-I elicited a small but significant (approximately 10%) vasoconstriction in all preglomerular vessels. These results indicate that the renal vascular effects of IGF-I involve activation of two endogenous vasodilators (NO and vasodilatory prostaglandins). In addition, IGF-I may also release an undefined vasoconstrictor.
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Affiliation(s)
- B Tönshoff
- Department of Pediatrics, State University of New York at Stony Brook 11794-8661, USA
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Casellas D, Bouriquet N, Herizi A. Bosentan prevents preglomerular alterations during angiotensin II hypertension. Hypertension 1997; 30:1613-20. [PMID: 9403591 DOI: 10.1161/01.hyp.30.6.1613] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The present study was performed to characterize structurofunctional alterations of preglomerular vessels during chronic angiotensin II (Ang II)-induced hypertension (Ang II group: 400 ng x kg[-1] x min[-1], 10 days) and to assess the role of endothelin-1 in rats receiving Ang II and the mixed receptor antagonist bosentan (Ang II+B group: 30 mg x kg[-1] x d[-1], 10 days). Systolic blood pressure rose by 56+/-3 and 54+/-6 mm Hg in Ang II and Ang II+B rats, respectively. Albuminuria increased similarly in both Ang II-treated groups, reflecting glomerular barrier dysfunction. Preglomerular vessels were isolated after HCI maceration and comprised arcuate arteries and their branches, interlobular arteries (ILA), and afferent arterioles (AA). In the Ang II group, focal vascular lesions affected 36+/-6%, 20+/-5%, and 4+/-1% of arcuate arterial branches, ILA, and AA, respectively. They were characterized by 74% increased media thickness and accumulation of Sudan black-positive (SB+) lipid droplets, and media cell proliferation was documented through immunohistochemistry. The occurrence of SB+ lesions was strikingly reduced with bosentan. Autoregulatory responses (AR) were assessed along ILA and AA with the use of blood-perfused juxtamedullary nephron preparations. AR were elicited by raising blood perfusion pressure from 60 to 160 mm Hg and quantified through videomicroscopy as pressure-induced constrictions. AR were inhibited in Ang II-treated rats along ILA and AA; Ang II-induced AR changes were prevented by bosentan. Maximal relaxation induced by Mn2+ revealed equal basal tone in Ang II-treated, Ang II+B-treated, and control vessels. Chronic Ang II-induced hypertension is therefore associated with the development of SB+ lesions and selective impairment of AR in juxtamedullary nephrons. Endothelin-1 likely mediates the structurofunctional alterations of preglomerular vasculature during Ang II hypertension.
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Affiliation(s)
- D Casellas
- Groupe Rein et Hypertension, Institut Universitaire de Recherche Clinique, Montpellier, France.
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Steinhausen M, Endlich K, Nobiling R, Parekh N, Schütt F. Electrically induced vasomotor responses and their propagation in rat renal vessels in vivo. J Physiol 1997; 505 ( Pt 2):493-501. [PMID: 9423188 PMCID: PMC1160079 DOI: 10.1111/j.1469-7793.1997.493bb.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
1. Vasomotor responses (VMR) induced by local electrical stimulation were studied in the vasculature of the split hydronephrotic rat kidney by in vivo microscopy. 2. Unipolar pulses, which were applied by a micropipette positioned close to the vessel wall, elicited local and propagated VMR. Depolarizing and hyperpolarizing currents caused vasoconstriction and vasodilatation, respectively. 3. The magnitude of VMR could be controlled within seconds by variation of pulse frequency, pulse width and voltage. VMR were abolished by slight retraction of the stimulating micropipette. Repetitive electrical stimulation resulted in reproducibly uniform VMR. 4. Propagated VMR decayed with increasing distance from the stimulation site. They decayed more rapidly in the upstream than in the downstream flow direction in interlobular arteries. The longitudinal decay was well approximated by an exponential function with significantly different length constants of 150 +/- 40 microns (upstream, n = 5) and 420 +/- 90 microns (downstream, n = 8). 5. Our results show that vasomotor responses, which are initiated by changes in membrane potential, are propagated over distances of potential physiological importance in interlobular arteries.
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Affiliation(s)
- M Steinhausen
- Institut für Anatomie und Zellbiologie I, Universität Heidelberg, Germany.
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Takenaka T, Kanno Y, Kitamura Y, Hayashi K, Suzuki H, Saruta T. Role of chloride channels in afferent arteriolar constriction. Kidney Int 1996; 50:864-72. [PMID: 8872961 DOI: 10.1038/ki.1996.386] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The effects of IAA-94, a chloride channel blocker and/or low chloride perfusate on afferent arteriolar (AA) constriction by angiotensin II (Ang II), norepinephrine (NE) and increasing pressure (80 to 160 mm Hg) were assessed using isolated perfused hydronephrotic kidneys. In the first series of experiments, Ang II (0.3 nM) constricted AAs by 33 +/- 3% (N = 5, P < 0.01). Subsequent addition of diltiazem (10 microM) restored the decrements in the AA diameters. In the presence of diltiazem (10 microM), increasing pressure did not constrict AAs. In the second series of experiments. elevation of pressure constricted AAs by 20 +/- 2% (N = 7. P < 0.01). Subsequent addition of IAA-94 (30 microM) failed to alter the basal AA diameter and myogenic responsiveness. However, Ang II-induced AA constriction was abolished by IAA-94. In the third series of experiments, decreasing extracellular chloride exaggerated AA constriction by 0.1 nM of Ang II (from 13 +/- 2 to 20 +/- 3%, N = 6, P < 0.05). Similarly, low chloride perfusate enhanced NE (0.1 microM)-induced AA constriction (from 14 +/- 2 to 19 +/- 2%, N = 6, P < 0.05). In contrast, myogenic responsiveness was not influenced by reducing chloride concentrations. The present data provide evidence that both Ang II and NE induce AA constriction by opening chloride channels and subsequent activation of voltage-dependent calcium channels, and suggest that the myogenic response is mediated by activating voltage-dependent calcium channels independently of chloride channels.
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Affiliation(s)
- T Takenaka
- Shinjuku Suimei Clinic, School of Medicine, Keio University, Tokyo, Japan
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van Lambalgen AA, Bouriquet N, Casellas D. Effects of endotoxin on tone and pressure-responsiveness of preglomerular juxtamedullary vessels. Pflugers Arch 1996; 432:574-7. [PMID: 8766020 DOI: 10.1007/s004240050172] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Endotoxin might affect renal vasoreactivity, but in vivo this is difficult to assess (systemic influences). Therefore, we used the in vitro blood-perfused juxtamedullary nephron preparation to study early changes in preglomerular vascular reactivity induced by exposure to endotoxin. Pressure-evoked vasomotor responses were determined videometrically by measuring steady-state inside vessel diameters at a perfusion pressure of 60 or 120 mmHg. Intraluminal application of endotoxin (primary contact with endothelium) for 120 min elicited an early (within 30 min) and sustained approximately 25% vasoconstriction from arcuate artery to the distal portions of the afferent arterioles; autoregulatory responses, indicated by pressure-induced vasoconstriction, were unchanged. When topically applied, endotoxin (primary contact with smooth muscle cells) had no vasomotor effects. Significant constrictions, and increases in autoregulatory responses were obtained when the preparation was taken from kidneys from endotoxin-treated rats. Endotoxin had no effect on efferent arteriolar dimensions. Such preferential preglomerular early vasoconstriction is consistent with the early increase in renal resistance and parallel decrease in renal blood flow and glomerular filtration observed during endotoxin shock in vivo. Our results support the concept of local, endothelium-mediated effects of endotoxin on renal vessels.
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Affiliation(s)
- A A van Lambalgen
- Laboratory for Physiology, Institute for Cardiovascular Research, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
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Ikenaga H, Fallet RW, Carmines PK. Contribution of tubuloglomerular feedback to renal arteriolar angiotensin II responsiveness. Kidney Int 1996; 49:34-9. [PMID: 8770946 DOI: 10.1038/ki.1996.5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The purpose of the present study was to test the hypothesis that a component of the afferent arteriolar vasoconstrictor response to angiotensin II (Ang II) requires an intact tubuloglomerular feedback (TGF) mechanism. Enalaprilat-treated male Sprague-Dawley rats served as tissue donors for study of renal microvascular function using the in vitro blood-perfused juxtamedullary nephron technique. Arteriolar lumen diameter responses to exogenous Ang II were determined before and after TGF blockade (papillectomy or 50 microM furosemide). Before TGF blockage, 10 nM Ang II significantly reduced diameters of both mid-afferent (53 +/- 5%) and efferent (43 +/- 9%) arterioles. TGF blockade did not alter baseline diameter of either arteriole, but significantly blunted the mid-afferent vasoconstriction evoked by 10 nM Ang II (44 +/- 7% inhibition by papillectomy; 43 +/- 10% inhibition by furosemide). Similar behavior was observed at afferent arteriolar sites near the glomerulus; however, efferent arteriolar Ang II responsiveness was not altered by papillectomy. The impact of TGF blockade on afferent arteriolar Ang II responsiveness was most prominent at high peptide concentrations (10 nM), while not significantly influencing the response to 1 nM Ang II. In contrast, the afferent vasoconstrictor effect of norepinephrine was unaffected by papillectomy. These data indicate that the vasoconstrictor influence of exogenous Ang II on afferent, but not efferent, arterioles of intact juxtamedullary nephrons includes both TGF-dependent and TGF-independent components.
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Affiliation(s)
- H Ikenaga
- Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha, USA
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Juncos LA, Garvin J, Carretero OA, Ito S. Flow modulates myogenic responses in isolated microperfused rabbit afferent arterioles via endothelium-derived nitric oxide. J Clin Invest 1995; 95:2741-8. [PMID: 7769114 PMCID: PMC295958 DOI: 10.1172/jci117977] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Flow may be a physiological stimulus of the endothelial release of nitric oxide (NO) and prostaglandins (PGs). We tested the hypothesis that pressure-induced constriction of the glomerular afferent arteriole (Af-Art) is modulated by luminal flow via endothelial production of NO. We microdissected the terminal segment of an interlobular artery together with two Af-Arts, their glomeruli (GL) and efferent arterioles (Ef-Art). The two Af-Arts were perfused simultaneously from the interlobular artery, while one Ef-Art was occluded. Since the arteriolar perfusate contained 5% albumin, oncotic pressure built up in the glomerulus with the occluded Ef-Art and opposed the force of filtration, resulting in little or no flow through the corresponding Af-Art. Thus this preparation allowed us to observe free-flow and no-flow Af-Arts simultaneously during stepwise 30-mmHg increases in intraluminal pressure (from 30 to 120 mmHg). Pressure-induced constriction was weaker in free-flow than no-flow Af-Arts, with the luminal diameter decreasing by 11.1 +/- 1.7 and 25.6 +/- 2.3% (n = 30), respectively, at 120 mmHg. To examine whether flow modulates myogenic constriction through endothelium-derived NO and/or PGs, we examined pressure-induced constriction before and after (a) disruption of the endothelium, (b) inhibition of NO synthesis with NW-nitro-L-arginine methyl ester (L-NAME), or (c) inhibition of cyclooxygenase with indomethacin. Both endothelial disruption and L-NAME augmented pressure-induced constriction in free-flow but not no-flow Af-Arts, abolishing the differences between the two. However, indomethacin had no effect in either free-flow or no-flow Af-Arts. These results suggest that intraluminal flow attenuates pressure-induced constriction in Af-Arts via endothelium-derived NO. Thus flow-stimulated NO release may be important in the fine control of glomerular hemodynamics.
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Affiliation(s)
- L A Juncos
- Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan 48202, USA
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Moore LC, Rich A, Casellas D. Ascending myogenic autoregulation: interactions between tubuloglomerular feedback and myogenic mechanisms. Bull Math Biol 1994; 56:391-410. [PMID: 8087076 DOI: 10.1007/bf02460464] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A mathematical model of the renal vascular and tubular systems was used to examine the possibility that synergistic interactions might occur between the tubuloglomerular feedback (TGF) and myogenic autoregulatory mechanisms in the kidney. To simulate the myogenic mechanism, the renal vasculature was modelled with a resistance network where the total preglomerular resistance varies with intravascular pressure. In addition, a steady-state model of glomerular filtration, proximal and Henle's loop reabsorption, and TGF-modulation of afferent arteriolar resistance was derived. The results show that, if TGF acts on the distal portion of the preglomerular vasculature, then any TGF-induced vasoconstriction should raise upstream intravascular pressure and, thereby, trigger a myogenic (AMYO) response. The model further predicts that the magnitude of the AMYO response can be similar in magnitude to the TGF-induced increment in afferent resistance. Hence, the effects of TGF excitation on whole kidney hemodynamics may be much greater than predicted from measurements in single nephrons. Moreover, a significant fraction of the intrinsic myogenic autoregulatory response to increased renal perfusion pressure may result from a synergistic interaction between the TGF and myogenic mechanisms.
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Affiliation(s)
- L C Moore
- Department of Physiology and Biophysics, State University of New York, Stony Brook 11794
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