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Exaggerated blood pressure response to fasudil or nifedipine in hypertensive Ren-2 transgenic rats: role of altered baroreflex. Hypertens Res 2018; 42:145-154. [PMID: 30518983 DOI: 10.1038/s41440-018-0146-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Revised: 04/18/2018] [Accepted: 05/25/2018] [Indexed: 11/08/2022]
Abstract
Basal calcium sensitization is decreased in spontaneously hypertensive rats, although their blood pressure (BP) response to acute Rho-kinase inhibition is enhanced. Using fasudil (Rho-kinase inhibitor) or nifedipine (L-VDCC blocker), we evaluated the contribution of calcium sensitization and calcium entry to BP maintenance in hypertensive transgenic Ren-2 rats (TGR) focusing on the influence of major vasoactive systems and/or baroreflex efficiency on BP responses to these two drugs. Homozygous TGR and normotensive Hannover Sprague-Dawley (HanSD) control rats aged 5, 11, or 22 weeks were used. The acute BP-lowering effects of fasudil or nifedipine were studied in intact rats, nitric oxide-deficient L-NAME-pretreated rats and rats subjected to combined blockade of the renin-angiotensin system (RAS), sympathetic nervous system (SNS) and nitric oxide synthase (NOS). Fasudil- or nifedipine-induced BP reduction increased during hypertension development in TGR. By contrast, the nifedipine-induced BP response decreased, whereas the fasudil-induced BP response increased with age in HanSD controls. Our data indicated a major contribution of nifedipine-sensitive calcium entry and relative attenuation of calcium sensitization in hypertensive rats compared with normotensive controls. The BP responses to fasudil or nifedipine were enhanced by NOS inhibition and combined blockade in normotensive HanSD rats but not in hypertensive TGR. In conclusion, calcium sensitization is attenuated by endogenous nitric oxide in normotensive HanSD rats but not in hypertensive TGR. Moreover, BP reduction elicited by acute Rho-kinase inhibition is partially compensated by enhanced sympathetic vasoconstriction. The decreased compensation in hypertensive rats with impaired baroreflex efficiency explains their greater BP response to fasudil than in normotensive animals.
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Fonkoue IT, Norrholm SD, Marvar PJ, Li Y, Kankam ML, Rothbaum BO, Park J. Elevated resting blood pressure augments autonomic imbalance in posttraumatic stress disorder. Am J Physiol Regul Integr Comp Physiol 2018; 315:R1272-R1280. [PMID: 30303706 DOI: 10.1152/ajpregu.00173.2018] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Posttraumatic stress disorder (PTSD) is characterized by increased sympathetic nervous system (SNS) activity, blunted parasympathetic nervous system (PNS) activity, and impaired baroreflex sensitivity (BRS), which contribute to accelerated cardiovascular disease. Patients with PTSD also have chronic stress-related elevations in resting blood pressure (BP), often in the prehypertensive range; yet, it is unclear if elevated resting blood pressure (ERBP) augments these autonomic derangements in PTSD. We hypothesized that compared with normotensive PTSD (N-PTSD), those with ERBP (E-PTSD) have further increased SNS, decreased PNS activity, and impaired BRS at rest and exaggerated SNS reactivity, PNS withdrawal, and pressor responses during stress. In 16 E-PTSD and 17 matched N-PTSD, we measured continuous BP, ECG, muscle sympathetic nerve activity (MSNA), and heart rate variability (HRV) markers reflecting cardiac PNS activity [standard deviation of R-R intervals (SDNN), root mean square of differences in successive R-R intervals (RMSSD), and high frequency power (HF)] during 5 min of rest and 3 min of mental arithmetic. Resting MSNA ( P = 0.943), sympathetic BRS ( P = 0.189), and cardiovagal BRS ( P = 0.332) were similar between groups. However, baseline SDNN (56 ± 6 vs. 78 ± 8 ms, P = 0.019), RMSSD (39 ± 6 vs. 63 ± 9 ms, P = 0.018), and HF (378 ± 103 vs. 693 ± 92 ms2, P = 0.015) were lower in E-PTSD versus N-PTSD. During mental stress, the systolic blood pressure response ( P = 0.011) was augmented in E-PTSD. Although MSNA reactivity was not different ( P > 0.05), the E-PTSD group had an exaggerated reduction in HRV during mental stress ( P < 0.05). PTSD with ERBP have attenuated resting cardiac PNS activity, coupled with exaggerated BP reactivity and PNS withdrawal during stress.
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Affiliation(s)
- Ida T Fonkoue
- Renal Division, Department of Medicine, Emory University School of Medicine , Atlanta, Georgia.,Research Service Line, Atlanta Veteran Affairs Medical Center, Decatur, Georgia
| | - Seth D Norrholm
- Mental Health Service Line, Atlanta Veteran Affairs Medical Center, Decatur, Georgia.,Psychiatry and Behavioral Sciences, Emory University , Atlanta, Georgia
| | - Paul J Marvar
- Department of Pharmacology and Physiology, Institute for Neuroscience, George Washington University , Washington, District of Columbia
| | - Yunxiao Li
- Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University , Atlanta, Georgia
| | - Melanie L Kankam
- Renal Division, Department of Medicine, Emory University School of Medicine , Atlanta, Georgia.,Research Service Line, Atlanta Veteran Affairs Medical Center, Decatur, Georgia
| | - Barbara O Rothbaum
- Department of Pharmacology and Physiology, Institute for Neuroscience, George Washington University , Washington, District of Columbia
| | - Jeanie Park
- Renal Division, Department of Medicine, Emory University School of Medicine , Atlanta, Georgia.,Research Service Line, Atlanta Veteran Affairs Medical Center, Decatur, Georgia
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Basal and Activated Calcium Sensitization Mediated by RhoA/Rho Kinase Pathway in Rats with Genetic and Salt Hypertension. BIOMED RESEARCH INTERNATIONAL 2017; 2017:8029728. [PMID: 28197417 PMCID: PMC5288518 DOI: 10.1155/2017/8029728] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Revised: 11/27/2016] [Accepted: 12/15/2016] [Indexed: 11/17/2022]
Abstract
Calcium sensitization mediated by RhoA/Rho kinase pathway can be evaluated either in the absence (basal calcium sensitization) or in the presence of endogenous vasoconstrictor systems (activated calcium sensitization). Our aim was to compare basal and activated calcium sensitization in three forms of experimental hypertension with increased sympathetic tone and enhanced calcium entry—spontaneously hypertensive rats (SHR), heterozygous Ren-2 transgenic rats (TGR), and salt hypertensive Dahl rats. Activated calcium sensitization was determined as blood pressure reduction induced by acute administration of Rho kinase inhibitor fasudil in conscious rats with intact sympathetic nervous system (SNS) and renin-angiotensin system (RAS). Basal calcium sensitization was studied as fasudil-dependent difference in blood pressure response to calcium channel opener BAY K8644 in rats subjected to RAS and SNS blockade. Calcium sensitization was also estimated from reduced development of isolated artery contraction by Rho kinase inhibitor Y-27632. Activated calcium sensitization was enhanced in all three hypertensive models (due to the hyperactivity of vasoconstrictor systems). In contrast, basal calcium sensitization was reduced in SHR and TGR relative to their controls, whereas it was augmented in salt-sensitive Dahl rats relative to their salt-resistant controls. Similar differences in calcium sensitization were seen in femoral arteries of SHR and Dahl rats.
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Schaich CL, Grabenauer M, Thomas BF, Shaltout HA, Gallagher PE, Howlett AC, Diz DI. Medullary Endocannabinoids Contribute to the Differential Resting Baroreflex Sensitivity in Rats with Altered Brain Renin-Angiotensin System Expression. Front Physiol 2016; 7:207. [PMID: 27375489 PMCID: PMC4899471 DOI: 10.3389/fphys.2016.00207] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 05/22/2016] [Indexed: 11/13/2022] Open
Abstract
CB1 cannabinoid receptors are expressed on vagal afferent fibers and neurons within the solitary tract nucleus (NTS), providing anatomical evidence for their role in arterial baroreflex modulation. To better understand the relationship between the brain renin-angiotensin system (RAS) and endocannabinoid expression within the NTS, we measured dorsal medullary endocannabinoid tissue content and the effects of CB1 receptor blockade at this brain site on cardiac baroreflex sensitivity (BRS) in ASrAOGEN rats with low glial angiotensinogen, normal Sprague-Dawley rats and (mRen2)27 rats with upregulated brain RAS expression. Mass spectrometry revealed higher levels of the endocannabinoid 2-arachidonoylglycerol in (mRen2)27 compared to ASrAOGEN rats (2.70 ± 0.28 vs. 1.17 ± 0.09 ng/mg tissue; P < 0.01), while Sprague-Dawley rats had intermediate content (1.85 ± 0.27 ng/mg tissue). Microinjection of the CB1receptor antagonist SR141716A (36 pmol) into the NTS did not change cardiac BRS in anesthetized Sprague-Dawley rats (1.04 ± 0.05 ms/mmHg baseline vs. 1.17 ± 0.11 ms/mmHg after 10 min). However, SR141716A in (mRen2)27 rats dose-dependently improved BRS in this strain: 0.36 pmol of SR141716A increased BRS from 0.43 ± 0.03 to 0.71 ± 0.04 ms/mmHg (P < 0.001), and 36 pmol of SR141716A increased BRS from 0.47 ± 0.02 to 0.94 ± 0.10 ms/mmHg (P < 0.01). In contrast, 0.36 pmol (1.50 ± 0.12 vs. 0.86 ± 0.08 ms/mmHg; P < 0.05) and 36 pmol (1.38 ± 0.16 vs. 0.46 ± 0.003 ms/mmHg; P < 0.01) of SR141716A significantly reduced BRS in ASrAOGEN rats. These observations reveal differential dose-related effects of the brain endocannabinoid system that influence cardiovagal BRS in animals with genetic alterations in the brain RAS.
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Affiliation(s)
- Chris L Schaich
- Department of Physiology and Pharmacology and Hypertension and Vascular Research Center, Wake Forest School of Medicine Winston-Salem, NC, USA
| | - Megan Grabenauer
- Department of Physiology and Pharmacology and Hypertension and Vascular Research Center, Wake Forest School of MedicineWinston-Salem, NC, USA; Analytical Chemistry and Pharmaceutics, RTI InternationalResearch Triangle Park, NC, USA
| | - Brian F Thomas
- Department of Physiology and Pharmacology and Hypertension and Vascular Research Center, Wake Forest School of MedicineWinston-Salem, NC, USA; Analytical Chemistry and Pharmaceutics, RTI InternationalResearch Triangle Park, NC, USA
| | - Hossam A Shaltout
- Department of Physiology and Pharmacology and Hypertension and Vascular Research Center, Wake Forest School of MedicineWinston-Salem, NC, USA; Department of Obstetrics and Gynecology, Wake Forest School of MedicineWinston-Salem, NC, USA
| | - Patricia E Gallagher
- Department of Physiology and Pharmacology and Hypertension and Vascular Research Center, Wake Forest School of Medicine Winston-Salem, NC, USA
| | - Allyn C Howlett
- Department of Physiology and Pharmacology and Hypertension and Vascular Research Center, Wake Forest School of Medicine Winston-Salem, NC, USA
| | - Debra I Diz
- Department of Physiology and Pharmacology and Hypertension and Vascular Research Center, Wake Forest School of Medicine Winston-Salem, NC, USA
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Diz DI, Arnold AC, Nautiyal M, Isa K, Shaltout HA, Tallant EA. Angiotensin peptides and central autonomic regulation. Curr Opin Pharmacol 2011; 11:131-7. [PMID: 21367658 DOI: 10.1016/j.coph.2011.02.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2011] [Accepted: 02/08/2011] [Indexed: 10/18/2022]
Abstract
Aging, hypertension, and fetal-programmed cardiovascular disease are associated with a functional deficiency of angiotensin (Ang)-(1-7) in the brain dorsomedial medulla. The resulting unrestrained activity of Ang II in brainstem regions negatively impacts resting mean arterial pressure, sympathovagal balance, and baroreflex sensitivity for control of heart rate. The differential effects of Ang II and Ang-(1-7) may be related to the cellular sources of these peptides as well as different precursor pathways. Long-term alterations of the brain renin-angiotensin system may influence signaling pathways including phosphoinositol-3-kinase and mitogen-activated protein kinase and their downstream mediators, and as a consequence may influence metabolic function. Differential regulation of signaling pathways in aging and hypertension by Ang II versus Ang-(1-7) may contribute to the autonomic dysfunction accompanying these states.
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Affiliation(s)
- Debra I Diz
- The Hypertension and Vascular Research Center, Wake Forest University School of Medicine, Winston-Salem, NC, USA.
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Goldman RK, Azar AS, Mulvaney JM, Hinojosa-Laborde C, Haywood JR, Brooks VL. Baroreflex sensitivity varies during the rat estrous cycle: role of gonadal steroids. Am J Physiol Regul Integr Comp Physiol 2009; 296:R1419-26. [PMID: 19261912 DOI: 10.1152/ajpregu.91030.2008] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Baroreflex sensitivity (BRS) increases in women during the luteal phase of the menstrual cycle, when gonadal hormones are elevated, but whether a similar cycle-dependent variation in BRS occurs in rats is unknown. In addition, whether cyclic BRS changes depend on gonadal steroids has not been previously investigated. To test these hypotheses, BRS was determined in cycling female rats using two approaches: 1) baroreflex control of renal sympathetic nerve activity (RSNA) in anesthetized rats; 2) cardiovagal spontaneous BRS (sBRS) in conscious rats instrumented for continuous telemetric measurements of mean arterial pressure (MAP) and heart rate (HR). MAP, HR, and sBRS were also measured in rats 2-3 and 5-6 wk following ovariectomy (OVX), to eliminate gonadal steroids. In anesthetized rats, RSNA BRS gain was increased (P < 0.01) during proestrus (-4.8+/-0.5% control/mmHg) compared with diestrus/estrus (-2.8 +/- 0.3% control/mmHg). Similarly, a proestrous peak in sBRS was observed in conscious rats (1.66 +/- 0.07 ms/mmHg, proestrus; 1.48 +/- 0.06 ms/mmHg, diestrus/estrus; P < 0.001). OVX eliminated estrous cycle-induced variation in sBRS. In addition, OVX reduced (P < 0.05) diurnal variations in MAP (5.9 +/- 0.3 vs. 3.9 +/- 0.5 mmHg) and HR [54 +/- 4 vs. 39 +/- 3 beats per minute (bpm)], and abolished diurnal variations in sBRS. Finally, while MAP, HR, and sBRS were decreased 2-3 wk following OVX, approximately 3 wk later, MAP and sBRS increased, and HR decreased further. No changes in MAP, HR, or sBRS were seen with time in sham OVX controls. In summary, RSNA and cardiovagal sBRS vary during the rat estrous cycle, and this variation is abolished by OVX. We conclude that sex steroid hormones are required for both cyclic and diurnal changes in BRS in rats.
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Affiliation(s)
- Robert K Goldman
- Portland Veteran Affairs Medical Center, Department of Surgery, Portland, Oregon, USA
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Angiotensin-(1-7) and baroreflex function in nucleus tractus solitarii of (mRen2)27 transgenic rats. J Cardiovasc Pharmacol 2008; 51:542-8. [PMID: 18475201 DOI: 10.1097/fjc.0b013e3181734a54] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
BACKGROUND Endogenous angiotensin (Ang)-(1-7) enhances, while Ang II attenuates, baroreceptor sensitivity (BRS) for reflex control of heart rate (HR) in Sprague-Dawley (SD) rats. In (mRen2)27 renin transgenic rats [(mRen2)], there is overexpression of the mouse Ren2 gene in brain, leading to elevated Ang II and reduced Ang-(1-7) in brain medullary, and associated with hypertension and impaired BRS. METHODS We therefore tested the contribution of endogenous Ang-(1-7) to BRS for control of HR and responses to cardiac vagal chemosensitive afferent fiber activation (CVA) with phenylbiguanide (PBG) in anesthetized SD and (mRen2) 27 rats before and after bilateral nucleus of the solitary tract (nTS) injection of the Ang-(1-7) receptor antagonist (D-Ala7)-Ang-(1-7). RESULTS (mRen2) 27 rats exhibited a approximately 50% impairment in BRS as compared with SD (P < 0.05). (D-Ala7)-Ang-(1-7) attenuated BRS by approximately 50% in SD rats, but was without effect in (mRen2) 27 rats. (D-Ala7)-Ang-(1-7) did not alter the responses to CVA by PBG (iv bolus) in either strain. There were no differences in the depressor effects of Ang-(1-7) injected into the nTS, nor were levels of mRNA different for angiotensin-converting enzyme, angiotensin-converting enzyme 2, neprilysin, or the mas receptor in medullary tissue from SD versus (mRen2)27 rats. CONCLUSION Endogenous Ang-(1-7) does not provide tonic input in the nTS to modulate BRS for control of HR in (mRen2)27 rats, which may contribute to impairment of BRS in these animals.
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Gao XY, Wang HJ, Zhang Y, Lu ZH, Wang W, Zhu GQ. Resetting blood pressure by a closed-loop implanted chip system in normotensive rats. Life Sci 2006; 78:1129-34. [PMID: 16168443 DOI: 10.1016/j.lfs.2005.06.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2005] [Accepted: 06/21/2005] [Indexed: 11/21/2022]
Abstract
A closed-loop implanted chip system was designed to control blood pressure without using drugs. The chip system instantaneously reset blood pressure by stimulating the left aortic depressor nerve according to the feedback signals of arterial blood pressure. The relationship between pressure signals and frequency of stimulation was identified in vitro and in vivo, and the efficiency of the chip system was evaluated in normal anesthetized Wistar rats. To determine whether the depressor effect of the chip was primarily independent on the bradycardia induced by the resetting, the effects of methyl atropine (1.5 g/kg, iv.) and bilateral vagotomy on depressor effect induced by the chip system were determined, respectively. The results indicated that the chip system worked well. The frequency of stimulus linearly increased following the elevation of pressure from 70 to 160 mm Hg. The frequency of the stimulus reached its maximum (100 Hz) when pressure exceeded 160 mm Hg, and the stimulation stopped when MAP was below 70 mm Hg. There were significant decreases in mean arterial pressure (MAP, -20.0+/-4.4 mm Hg) and heart rate (HR, -43.0+/-10.5 bpm) during the resetting in rats. After resetting, both MAP and HR recovered in a minute without any significant rebound. Pretreatment with either methyl atropine or bilateral vagotomy abolished the bradycardia effect but produced no significant effect on hypotension. The results demonstrated that the chip system successfully reset blood pressure in rats, and that the hypotension induced by the chip system was primarily independent on the bradycardia effect.
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Affiliation(s)
- Xing-Ya Gao
- Department of Physiology, Nanjing Medical University, Nanjing, 210029, China
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Veerasingham SJ, Raizada MK. Brain renin-angiotensin system dysfunction in hypertension: recent advances and perspectives. Br J Pharmacol 2003; 139:191-202. [PMID: 12770924 PMCID: PMC1573858 DOI: 10.1038/sj.bjp.0705262] [Citation(s) in RCA: 207] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2003] [Accepted: 02/27/2003] [Indexed: 11/08/2022] Open
Abstract
This review focuses on the dysfunction of the intrinsic brain renin-angiotensin system (RAS) in the pathogenesis of hypertension. Hyperactivity of the brain RAS plays a critical role in mediating hypertension in both humans and animal models of hypertension, including the spontaneously hypertensive rat (SHR). The specific mechanisms by which increased brain RAS activity results in hypertension are not well understood but include increases in sympathetic vasomotor tone and impaired arterial baroreflex function. We discuss the contribution of endogenous angiotensin (Ang) II actions on presympathetic vasomotor rostral ventrolateral medulla neurons to enhance sympathetic activity and maintain hypertension. In addition, we discuss Ang II-induced attenuation of afferent baroreceptor feedback within the nucleus tractus solitarius and its relevance to the development of hypertension. We also outline the cellular and molecular mechanisms of Ang II signal transduction that may be critical for the initiation and establishment of hypertension. In particular, we present evidence for a phosphoinositide-3-kinase-dependent signaling pathway that appears to contribute to hypertension in the SHR, possibly via augmented Ang II-induced increases in neuronal firing rate and enhanced transcriptional noradrenaline neuromodulation. Finally, we outline future directions in utilizing our understanding of the brain RAS dysfunction in hypertension for the development of improved therapeutic intervention in hypertension.
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Affiliation(s)
| | - Mohan K Raizada
- Department of Physiology and Functional Genomics, University of Florida, U.S.A
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Affiliation(s)
- Michael Bader
- From the Max-Delbrück-Center for Molecular Medicine (M.B., D.G.), Berlin-Buch, Germany; and the Department of Clinical Pharmacology (D.G.), University Hospital Benjamin Franklin, Free University, Berlin, Germany
| | - Detlev Ganten
- From the Max-Delbrück-Center for Molecular Medicine (M.B., D.G.), Berlin-Buch, Germany; and the Department of Clinical Pharmacology (D.G.), University Hospital Benjamin Franklin, Free University, Berlin, Germany
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