Adrenal and circulating renin-angiotensin system in stroke-prone hypertensive rats

Contribution of afferent renal nerve signals to acute and chronic blood pressure regulation in stroke-prone spontaneously hypertensive rats

The activation of sympathetic nervous system plays a critical role in the development of hypertension. The input from afferent renal nerves may affect central sympathetic outflow; however, its contribution to the development of hypertension remains unclear. We investigated the role of afferent renal nerves in acute and chronic blood pressure regulation using normotensive Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Acute chemical stimulation of afferent renal nerves elicited larger increases in blood pressure and renal sympathetic nerve activity in young 9-week-old SHRSP compared to WKY. Selective afferent renal denervation (ARDN) and conventional total renal denervation (TRDN) ablating both afferent and efferent nerves in young SHRSP revealed that only TRDN, but not ARDN, chronically attenuated blood pressure elevation. ARDN did not affect plasma renin activity or plasma angiotensin II levels, whereas TRDN decreased both. Neither TRDN nor ARDN affected central sympathetic outflow and systemic sympathetic activity determined by neuronal activity in the parvocellular region of hypothalamic paraventricular nucleus and rostral ventrolateral medulla and by plasma and urinary norepinephrine levels, respectively. Renal injury was not apparent in young SHRSP compared with WKY, suggesting that renal afferent input might not be activated in young SHRSP. In conclusion, the chronic input from afferent renal nerves does not contribute to the development of hypertension in SHRSP despite the increased blood pressure response to the acute stimulation of afferent renal nerves. Efferent renal nerves may be involved in the development of hypertension via activation of the renin-angiotensin system in SHRSP.

Mineralocorticoid receptor antagonism improves transient receptor potential vanilloid 4-dependent dilation of cerebral parenchymal arterioles and cognition in a genetic model of hypertension

OBJECTIVE

In a model of secondary hypertension, mineralocorticoid receptor (MR) antagonism during the development of hypertension prevents the impairment of transient receptor potential vanilloid 4 (TRPV4) activation in parenchymal arterioles (PAs) and cognitive impairment. However, it is unknown whether MR antagonism can improve these impairments when treatment begins after the onset of essential hypertension. We tested the hypothesis that MR activation in stroke-prone spontaneously hypertensive rats (SHRSP) leads to impaired TRPV4-mediated dilation in PAs that is associated with cognitive dysfunction and neuroinflammation.

METHODS

20-22-week-old male SHRSP ± eplerenone (EPL; 100 mg/kg daily for 4 weeks) were compared to normotensive Sprague-Dawley (SD) rats. Pressure myography was used to assess PA function. Cognition was tested using Y-maze. Neuroinflammation was assessed using immunofluorescence and qRT-PCR.

RESULTS

Carbachol-mediated endothelium-dependent dilation was impaired in SHRSP, and MR antagonism improved this without affecting myogenic tone. Dilation to TRPV4 agonist GSK1016790A was impaired in SHRSP, and ELP treatment restored this. Intermediate conductance potassium channel (IKCa)/small conductance potassium channel (SKCa)-mediated dilation was impaired by hypertension and unaffected by EPL treatment. TRPV4 and IKCa/SKCa channel mRNA expression were reduced in PAs from hypertensive rats, and EPL did not improve this. Impairments in PA dilation in SHRSP were associated with cognitive decline, microglial activation, reactive astrogliosis, and neuroinflammation; cognitive and inflammatory changes were improved with MR blockade.

CONCLUSIONS

These data advance our understanding of the effects of hypertension on cerebral arterioles using a clinically relevant model and treatment paradigm. Our studies suggest TRPV4 and the MR are potential therapeutic targets to improve cerebrovascular function and cognition during hypertension.

Cerebro-Cardiovascular Risk, Target Organ Damage, and Treatment Outcomes in Primary Aldosteronism

Primary aldosteronism (PA) is the most common type of endocrine hypertension, and numerous experimental and clinical evidence have verified that prolonged exposure to excess aldosterone is responsible for an increased risk of cerebro-cardiovascular events and target organ damage (TOD) in patients with PA. Therefore, focusing on restoring the toxic effects of excess aldosterone on the target organs is very important to reduce cerebro-cardiovascular events. Current evidence convincingly demonstrates that both surgical and medical treatment strategies would benefit cerebro-cardiovascular outcomes and mortality in the long term. Understanding cerebro-cardiovascular risk in PA would help clinical doctors to achieve both early diagnosis and treatment. Therefore, in this review, we will summarize the cerebro-cardiovascular risk in PA, focusing on the TOD of aldosterone, including brain, heart, vascular system, renal, adipose tissues, diabetes, and obstructive sleep apnea (OSA). Furthermore, the various treatment outcomes of adrenalectomy and medical treatment for patients with PA will also be discussed. We hope this knowledge will help improve cerebro-cardiovascular prognosis and reduce the incidence and mortality of cerebro-cardiovascular events in patients with PA.

Salt loading decreases urinary excretion and increases intracellular accumulation of uromodulin in stroke-prone spontaneously hypertensive rats

Uromodulin (UMOD) is the most abundant renal protein secreted into urine by the thick ascending limb (TAL) epithelial cells of the loop of Henle. Genetic studies have demonstrated an association between UMOD risk variants and hypertension. We aimed to dissect the role of dietary salt in renal UMOD excretion in normotension and chronic hypertension. Normotensive Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) (n=8/sex/strain) were maintained on 1% NaCl for 3 weeks. A subset of salt-loaded SHRSP was treated with nifedipine. Salt-loading in SHRSP increased blood pressure (ΔSBP 35 ± 5 mmHg, P<0.0001) and kidney injury markers such as kidney injury marker-1 (KIM-1; fold change, FC 3.4; P=0.003), neutrophil gelatinase-associated lipocalin (NGAL; FC, 2.0; P=0.012) and proteinuria. After salt-loading there was a reduction in urinary UMOD excretion in WKY and SHRSP by 26 and 55% respectively, compared with baseline. Nifedipine treatment reduced blood pressure (BP) in SHRSP, however, did not prevent salt-induced reduction in urinary UMOD excretion. In all experiments, changes in urinary UMOD excretion were dissociated from kidney UMOD protein and mRNA levels. Colocalization and ex-vivo studies showed that salt-loading increased intracellular UMOD retention in both WKY and SHRSP. Our study provides novel insights into the interplay among salt, UMOD, and BP. The role of UMOD as a cardiovascular risk marker deserves mechanistic reappraisal and further investigations based on our findings.

The Transient Receptor Potential Vanilloid 4 Channel and Cardiovascular Disease Risk Factors

Vascular endothelial cells regulate arterial tone through the release of nitric oxide and other diffusible factors such as prostacyclin and endothelium derived hyperpolarizing factors. Alongside these diffusible factors, contact-mediated electrical propagation from endothelial cells to smooth muscle cells via myoendothelial gap junctions, termed endothelium-dependent hyperpolarization (EDH), plays a critical role in endothelium-dependent vasodilation in certain vascular beds. A rise in intracellular Ca²⁺ concentration in endothelial cells is a prerequisite for both the production of diffusible factors and the generation of EDH, and Ca²⁺ influx through the endothelial transient receptor potential vanilloid 4 (TRPV4) ion channel, a nonselective cation channel of the TRP family, plays a critical role in this process in various vascular beds. Emerging evidence suggests that the dysregulation of endothelial TRPV4 channels underpins endothelial dysfunction associated with cardiovascular disease (CVD) risk factors, including hypertension, obesity, diabetes, and aging. Because endothelial dysfunction is a precursor to CVD, a better understanding of the mechanisms underlying impaired TRPV4 channels could lead to novel therapeutic strategies for CVD prevention. In this mini review, we present the current knowledge of the pathophysiological changes in endothelial TRPV4 channels associated with CVD risk factors, and then explore the underlying mechanisms involved.

Impact of angiotensin-converting enzyme inhibition on platelet tissue factor expression in stroke-prone rats

Supplemental Digital Content is available in the text

Objective:

Hypertension is a well known risk factor for thrombotic events such as myocardial infarction and stroke. Platelets express tissue factor (TF), the key activator of blood coagulation and thrombus formation. The number of TF-positive platelets increases in pathological conditions characterized by thrombotic complications but whether this occurs in hypertension is unknown. Here we investigated whether platelet TF expression is increased in a hypertensive status through a mechanism acting on megakaryocytes; the phenomenon could be modulated by antihypertensive drug as captopril; angiotensin (AngII) influences platelet TF expression.

Methods:

Spontaneously hypertensive stroke prone (SHRSP) rats received standard diet (StD) or a Japanese high-salt permissive diet (JpD). After 3 weeks, JpD animals were randomized to receive captopril or vehicle. Normotensive Wistar Kyoto (WKY) rats were used as controls. Cell-associated TF expression and activity were analyzed by flow cytometry and calibrated automated thrombogram, respectively.

Results:

Hypertensive StD-SHRSP showed an increased number of TF-positive platelets compared with normotensive WKY. After JpD administration, SHRSP developed severe hypertension and renal damage; the number of TF-positive megakaryocytes significantly increased compared with StD-SHRSP resulting in a higher number of TF-positive platelets with a faster kinetic of thrombin generation. These effects were reverted by captopril. Ex-vivo stimulation of platelets, isolated from normotensive WKY and from healthy individuals, with AngII induced a concentration-dependent increase of surface-associated TF expression.

Conclusion:

The current study shows for the first time that in hypertension the number of TF-positive megakaryocytes increases thus releasing in the circulation more platelets carrying a functionally active TF. AngII stimulates platelets to express TF.

Utilizing proteomics to understand and define hypertension: where are we and where do we go?

INTRODUCTION

Hypertension is a complex and multifactorial cardiovascular disorder. With different mechanisms contributing to a different extent to an individual's blood pressure, the discovery of novel pathogenetic principles of hypertension is challenging. However, there is an urgent and unmet clinical need to improve prevention, detection, and therapy of hypertension in order to reduce the global burden associated with hypertension-related cardiovascular diseases. Areas covered: Proteomic techniques have been applied in reductionist experimental models including angiotensin II infusion models in rodents and the spontaneously hypertensive rat in order to unravel mechanisms involved in blood pressure control and end organ damage. In humans proteomic studies mainly focus on prediction and detection of organ damage, particularly of heart failure and renal disease. While there are only few proteomic studies specifically addressing human primary hypertension, there are more data available in hypertensive disorders in pregnancy, such as preeclampsia. We will review these studies and discuss implications of proteomics on precision medicine approaches. Expert commentary: Despite the potential of proteomic studies in hypertension there has been moderate progress in this area of research. Standardized large-scale studies are required in order to make best use of the potential that proteomics offers in hypertension and other cardiovascular diseases.

Cellular mechanisms of metabolic syndrome-related atrial decompensation in a rat model of HFpEF

Heart failure (HF) with preserved ejection fraction (HFpEF) is present in about 50% of HF patients. Atrial remodeling is common in HFpEF and associated with increased mortality. We postulate that atrial remodeling is associated with atrial dysfunction in vivo related to alterations in cardiomyocyte Calcium (Ca) signaling and remodeling. We examined atrial function in vivo and Ca transients (CaT) (Fluo4-AM, field stim) in atrial cardiomyocytes of ZSF-1 rats without (Ln; lean hypertensive) and with metabolic syndrome (Ob; obese, hypertensive, diabetic) and HFpEF.

RESULTS

At 21weeks Ln showed an increased left ventricular (LV) mass and left ventricular end-diastolic pressure (LVEDP), but unchanged left atrial (LA) size and preserved atrial ejection fraction vs. wild-type (WT). CaT amplitude in atrial cardiomyocytes was increased in Ln (2.9±0.2 vs. 2.3±0.2F/F₀ in WT; n=22 cells/group; p<0.05). Studying subcellular Ca release in more detail, we found that local central cytosolic CaT amplitude was increased, while subsarcolemmal CaT amplitudes remained unchanged. Moreover, Sarcoplasmic reticulum (SR) Ca content (caffeine) was preserved while Ca spark frequency and tetracaine-dependent SR Ca leak were significantly increased in Ln. Ob mice developed a HFpEF phenotype in vivo, LA area was significantly increased and atrial in vivo function was impaired, despite increased atrial CaT amplitudes in vitro (2.8±0.2; p<0.05 vs. WT). Ob cells showed alterations of the tubular network possibly contributing to the observed phenotype. CaT kinetics as well as SR Ca in Ob were not significantly different from WT, but SR Ca leak remained increased. Angiotensin II (Ang II) reduced in vitro cytosolic CaT amplitudes and let to active nuclear Ca release in Ob but not in Ln or WT.

SUMMARY

In hypertensive ZSF-1 rats, a possibly compensatory increase of cytosolic CaT amplitude and increased SR Ca leak precede atrial remodeling and HFpEF. Atrial remodeling in ZSF-1 HFpEF is associated with an altered tubular network in-vitro and atrial contractile dysfunction in vivo, indicating insufficient compensation. Atrial cardiomyocyte dysfunction in vitro is induced by the addition of angiotensin II.

Common Impact of Chronic Kidney Disease and Brain Microhemorrhages on Cerebral Aβ Pathology in SHRSP

While chronic kidney disease seems to be an independent risk factor for cognitive decline, its impact on cerebral amyloid-β (Aβ) depositions, one hallmark of Alzheimer's Disease (AD) pathology, has not been investigated. Utilizing 80 male nontransgenic spontaneously hypertensive stroke prone rats (SHRSP) at various ages (12 to 44 weeks), tubulointerstitial renal damage, prevalence of cerebral microhemorrhages and Aβ accumulations were quantified. Using age-adjusted general linear models we investigated the main and interaction effects of renal damage and cerebral microhemorrhages on cerebral Aβ load. In addition, using post mortem human brain tissue of 16 stroke patients we examined the co-localization of perivascular Aβ deposits and small vessel wall damage. Statistical models revealed an age-independent main effect of tubulointerstitial kidney damage on brain Aβ accumulations, which was reinforced by the consecutive presence of cerebral microhemorrhages. Moreover, cerebral microhemorrhages independently predicted brain Aβ burden in SHRSP. In up to 69% of all human cases perivascular Aβ deposits were detected in the direct vicinity of small vessel wall damage. Our results support the associations between vascular pathology and Aβ deposition, and demonstrate a relationship between chronic kidney disease and cerebral Aβ pathology. Hence, our data suggest that prevention of chronic renal damage may reduce cerebral Aβ pathology.

Renin knockout rat: control of adrenal aldosterone and corticosterone synthesis in vitro and adrenal gene expression

The classic renin-angiotensin system is partly responsible for controlling aldosterone secretion from the adrenal cortex via the peptide angiotensin II (ANG II). In addition, there is a local adrenocortical renin-angiotensin system that may be involved in the control of aldosterone synthesis in the zona glomerulosa (ZG). To characterize the long-term control of adrenal steroidogenesis, we utilized adrenal glands from renin knockout (KO) rats and compared steroidogenesis in vitro and steroidogenic enzyme expression to wild-type (WT) controls (Dahl S rat). Adrenal capsules (ZG; aldosterone production) and subcapsules [zona reticularis/fasciculata (ZFR); corticosterone production] were separately dispersed and studied in vitro. Plasma renin activity and ANG II concentrations were extremely low in the KO rats. Basal and cAMP-stimulated aldosterone production was significantly reduced in renin KO ZG cells, whereas corticosterone production was not different between WT and KO ZFR cells. As expected, adrenal renin mRNA expression was lower in the renin KO compared with the WT rat. Real-time PCR and immunohistochemical analysis showed a significant decrease in P450aldo (Cyp11b2) mRNA and protein expression in the ZG from the renin KO rat. The reduction in aldosterone synthesis in the ZG of the renin KO adrenal seems to be accounted for by a specific decrease in P450aldo and may be due to the absence of chronic stimulation of the ZG by circulating ANG II or to a reduction in locally released ANG II within the adrenal gland.

Involvement of the AT1 receptor in the venoconstriction induced by angiotensin II in both the inferior vena cava and femoral vein

Although angiotensin II-induced venoconstriction has been demonstrated in the rat vena cava and femoral vein, the angiotensin II receptor subtypes (AT(1) or AT(2)) that mediate this phenomenon have not been precisely characterized. Therefore, the present study aimed to characterize the pharmacological receptors involved in the angiotensin II-induced constriction of rat venae cavae and femoral veins, as well as the opposing effects exerted by locally produced prostanoids and NO upon induction of these vasomotor responses. The obtained results suggest that both AT(1) and AT(2) angiotensin II receptors are expressed in both veins. Angiotensin II concentration-response curves were shifted toward the right by losartan but not by PD 123319 in both the vena cava and femoral vein. Moreover, it was observed that both 10(-5)M indomethacin and 10(-4)M L-NAME improve the angiotensin II responses in the vena cava and femoral vein. In conclusion, in the rat vena cava and femoral vein, angiotensin II stimulates AT(1) but not AT(2) to induce venoconstriction, which is blunted by vasodilator prostanoids and NO.

Aliskiren enhances protective effects of valsartan against type 2 diabetic nephropathy in mice

OBJECTIVES

Addition of aliskiren, a direct renin inhibitor, to losartan provides additive reduction of urinary albumin excretion in type 2 diabetic patients. However, the detailed effect of aliskiren on type 2 diabetic nephropathy is still unknown. This study was undertaken to examine the efficacy of aliskiren and the combination of aliskiren with valsartan on type 2 diabetic nephropathy.

METHODS

db/db mice were treated with aliskiren (3 mg/kg per day), valsartan (5 or 10 mg/kg per day), combined aliskiren (3 mg/kg per day) and valsartan (5 mg/kg per day), and hydralazine (80 mg/kg per day), for 6 weeks, and the protective effects against diabetic nephropathy were compared among each group.

RESULTS

Aliskiren significantly attenuated albuminuria and glomerular mesangial matrix expansion in db/db mice, which was associated with the improvement of the increased glomerular transforming growth factor-beta and type IV collagen expressions, the increased macrophage infiltration, and the decreased glomerular nephrin expression of db/db mice. These protective effects of aliskiren in db/db mice were attributed to the attenuation of p22(phox)-related nicotinamide adenine dinucleotide phosphate oxidase-induced superoxide. Addition of aliskiren to valsartan treatment provided more beneficial effects on all the above-mentioned parameters than valsartan monotherapy.

CONCLUSION

Aliskiren protected against type 2 diabetic nephropathy, through pleiotropic effects, and significantly enhanced the protective effects of valsartan against diabetic nephropathy in db/db mice.

Hypertension-induced vascular remodeling contributes to reduced cerebral perfusion and the development of spontaneous stroke in aged SHRSP rats

Stroke in spontaneously-hypertensive, stroke-prone (SHRSP) rats is of particular interest because the pathogenesis is believed to be similar to that in the clinical setting. In this study, we employed multi-modal MRI-ASL, DWI, T(2), GRE, T(1) (pre/post contrast)-to investigate the natural history of spontaneous cerebral infarction and the specific role of cerebral perfusion in disease development. Twelve female SHRSP rats (age: approximately 1 year) were imaged within 1 to 3 days of symptom onset. The distribution of ischemic lesions was the following: 28.1% visual, 21.9% striatal, 18.8% motorsensory, 12.5% thalamic, 12.5% auditory, 3.1% frontal/prelimbic, and 3.1% multiple areas. Ischemic lesions had significantly reduced blood flow in comparison with healthy tissue. Ischemic lesions were characterized by hyperplastic, thrombosed, and compressed vessels. These findings suggest that ischemic lesion development is related to hypertension-induced vascular remodeling and persistent hypoperfusion. This model should be useful for studying the relationship between chronic hypertension and subsequent stroke, both in terms of primary and secondary prevention.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Differential roles of renin and angiotensinogen in the feto-maternal interface in the development of complications of pregnancy

We previously identified a transgenic mouse model that developed pregnancy-associated hypertension (PAH) and intrauterine growth restriction (IUGR) by mating females expressing human angiotensinogen (hANG) with males expressing human renin (hRN). These phenotypic defects were not observed in the opposite type of mating combination, despite the feto-placental overexpression of hRN and hANG detected in both types of crossbreeding. Detailed analysis of transgene localization in the labyrinth and its permeability to the maternal circulation revealed that hRN produced in trophoblast giant cells was secreted into the maternal circulation, whereas hANG, produced in chorionic trophoblasts and trophoblastic epithelium, was undetectable in the maternal plasma, probably due to their distinct spatial and temporal expression in labyrinth. These results demonstrated that PAH and IUGR could be mediated by feto-placental hRN through its permeability to the maternal circulation, not by feto-placental hANG production. Furthermore, overexpression of maternally derived hANG in decidua and spiral arteries of pregnant females with PAH and IUGR raises the possibility of local activation of the renin-angiotensin system and its pathophysiological effects on placental hypoperfusion in complications of pregnancy. This study provides in vivo evidence that the cell-specific expression of RN and ANG in the feto-maternal interface impacts their differential roles in pregnancy.

Genetic disruption of atrial natriuretic peptide receptor-A alters renin and angiotensin II levels

We have studied cardiovascular and renal phenotypes in Npr1 (genetic determinant of natriuretic peptide receptor-A; NPRA) gene-disrupted mutant mouse model. The baseline systolic arterial pressure (SAP) in 0-copy mutant (-/-) mice (143 +/- 2 mmHg) was significantly higher than in 2-copy wild-type (+/+) animals (104 +/- 2 mmHg); however, the SAP in 1-copy heterozygotes (+/-) was at an intermediate value (120 +/- 4 mmHg). To determine whether Npr1 gene function affects the renin-angiotensin-aldosterone system (RAAS), we measured the components of RAAS in plasma, kidney, and adrenal gland of 0-copy, 1-copy, and 2-copy male mice. Newborn (2 days after the birth) 0-copy pups showed 2.5-fold higher intrarenal renin contents compared with 2-copy wild-type counterparts (0-copy 72 +/- 12 vs. 2-copy 30 +/- 7 microg ANG I. mg protein(-1). h(-1), respectively). The intrarenal ANG II level in 0-copy pups was also higher than in 2-copy controls (0-copy 33 +/- 5 vs. 2-copy 20 +/- 2 pg/mg protein, respectively). However, both young (3 wk) and adult (16 wk) 0-copy mutant mice showed a dramatic 50-80% reduction in plasma renin concentrations (PRCs) and in expression of renal renin message compared with 2-copy control animals. In contrast, the adrenal renin content and mRNA expression levels were 1.5- to 2-fold higher in 0-copy adult mice than in 2-copy animals. The results suggest that inhibition of renal and systemic RAAS is a compensatory response that prevents greater increases in elevated arterial pressures in adult NPRA null mutant mice. However, the greater renin and ANG II levels seen in 0-copy newborn pups provide evidence that the direct effect of NPRA activation on renin is an inhibitory response.

Spironolactone reduces cerebral infarct size and EGF-receptor mRNA in stroke-prone rats

Remodeling of the cerebral vasculature contributes to the pathogenesis of cerebral ischemia. Remodeling is caused by increased smooth muscle proliferation and may be due to an increase in the responsiveness of vascular cells to epidermal growth factor (EGF). Aldosterone is a risk factor for stroke, and the literature suggests it may play a role in increasing the expression of the receptor for EGF (EGFR). We hypothesized that mRNA for the EGF-stimulated pathway would be elevated in the vasculature of stroke-prone spontaneously hypertensive rats (SHRSP) and that this and experimental ischemic cerebral infract size would be reduced by aldosterone inhibition with spironolactone. We found that spironolactone treatment reduced the size of cerebral infarcts after middle cerebral artery occlusion in SHRSP (51.69 +/- 3.60 vs. 22.00 +/- 6.69% of hemisphere-infarcted SHRSP vs. SHRSP + spironolactone P < 0.05). Expression of EGF and EGFR mRNA was higher in cerebral vessels and aorta from adult SHRSP compared with Wistar-Kyoto rats. Only the expression of EGFR mRNA was elevated in the young SHRSP. Spironolactone reduced the EGFR mRNA expression in the aorta (1.09 +/- 0.25 vs. 0.56 +/- 0.11 phosphorimage units SHRSP vs. SHRSP + spironolactone P < 0.05) but had no effect on EGF mRNA. In vitro incubation of aorta with aldosterone +/- spironolactone produced similar results, suggesting a direct effect of aldosterone. Thus spironolactone may reduce the size of cerebral infarcts via a reduction in the expression of the EGFR mRNA, leading to reduced remodeling.

Mineralocorticoids upregulate arterial contraction to epidermal growth factor

The present studies test the hypothesis that contraction to EGF is dependent on mineralocorticoids and/or an elevation in systolic blood pressure (SBP). Endothelium-denuded thoracic aortas from sham normotensive, N(omega)-nitro-L-arginine (L-NNA) hypertensive, Wistar-Kyoto (WKY), and spontaneously hypertensive rats (SHR) were used in isolated tissue-bath experiments. Maximal contraction to epidermal growth factor [EGF; percentage of phenylephrine (PE; 10 umol/l)-induced contraction] was greater in strips from L-NNA (32 +/- 5%) and SHR (53 +/- 8%) rats compared with sham and WKY rats (17 +/- 1 and 12 +/- 4%, respectively). Wistar-Furth rats became only mildly hypertensive when given DOCA salt (134 +/- 6 mmHg) compared with Wistar rats (176 +/- 9 mmHg), but aortas from both strains had a similarly enhanced contraction to EGF (approximately 9 times the maximal contraction of sham aorta). Furthermore, in vitro incubation of aortas from Wistar and Wistar-Furth rats with aldosterone (10 nmol/l) increased EGF-receptor mRNA expression by >50%. These data indicate that arterial contraction to EGF may occur independent of hypertension and be stimulated by mineralocorticoids.

Subcellular localization of angiotensin II in kidney and adrenal

OBJECTIVES

To investigate whether tissue angiotensin II generation occurs intra- or extracellularly, we studied the subcellular localization of angiotensin II in kidney and adrenal, two organs with high endogenous angiotensin II concentrations.

DESIGN AND METHODS

Tissues were obtained, following a 1 h infusion of 125I-angiotensin I or 125I-angiotensin II to simultaneously determine the localization of plasma-derived angiotensin II, from five control pigs and four pigs that had been pretreated with the AT1 receptor antagonist eprosartan. Subcellular organelles, prepared by differential centrifugation from homogenized tissue, were characterized using organelle-specific markers.

RESULTS

125I-angiotensin II and angiotensin II were present in all organelles, with identical distribution profiles. In mitochondria-enriched fractions the relative specific activities [RSAs = (concentration per mg protein in fraction)/(concentration per mg protein in homogenate)] of the two peptides were similar to those in homogenate, whereas in cytosol-enriched fractions their RSAs were five- to 10-fold lower (P< 0.05 versus homogenate). In microsome- as well as in lysosome-enriched fractions the RSAs of 125I-angiotensin II and angiotensin II were two- to four-fold higher than in homogenate (P < 0.05), and their RSAs were also higher in renal nuclei-enriched fractions (P< 0.05). Eprosartan increased plasma angiotensin II to a larger degree than tissue angiotensin II and greatly reduced tissue 125I-angiotensin II. This led to similar decreases in the tissue/plasma concentration ratios of 125I-angiotensin II and angiotensin II. The subcellular distribution of both angiotensin II peptides was not affected by eprosartan.

CONCLUSIONS

Local angiotensin II synthesis in adrenal and kidney occurs predominantly extracellularly, and is followed by rapid AT1 receptor-mediated endocytosis, thereby leading to high intracellular angiotensin II levels.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

Anti-atherosclerotic effects of an angiotensin converting enzyme inhibitor and an angiotensin II antagonist in Cynomolgus monkeys fed a high-cholesterol diet

1. We investigated the relationship between angiotensin II formation and the development of atherosclerotic lesions in the aorta of monkeys (Macaca fascicularis) fed a high-cholesterol (4% cholesterol and 6% corn oil) diet for 6 months, and studied the effects of an angiotensin converting enzyme (ACE) inhibitor, trandolapril (10 mg kg-1 per day, p.o.), and an angiotensin II type 1 receptor antagonist, 2-butyl-4-(methylthio)-1-[[2'[[[(propylamino)carbonyl]amino]sulfonyl] (1,1'-biphenyl)-4-yl]methyl]-1H-imidazole-5-carboxylate (HR 720; 20 mg kg-1 per day, p.o.). 2. The level of low-density lipoprotein was significantly increased by the cholesterol diet, whereas that of high-density lipoprotein was significantly decreased. The relative areas of the atherosclerotic lesions in the thoracic aorta in the normal and cholesterol-diet groups were 1.3+/-0.3 and 64+/-10%, respectively. 3. Plasma renin and ACE activities showed no differences between the normal and cholesterol-diet groups. ACE activity and the concentration of angiotensin II were significantly increased in the aorta of the cholesterol-fed monkeys. 4. Trandolapril and HR 720 decreased significantly the area of the atherosclerotic lesions in the thoracic aorta of cholesterol-fed monkeys, but not the mean blood pressure and the levels of low-density and high-density lipoproteins. 5. In plasma and aorta, trandolapril, but not HR 720, decreased significantly the ACE activities in the cholesterol-fed monkeys, while both of these drugs decreased significantly the angiotensin II levels. 6. In conclusion, blockade of angiotensin II function in vascular tissues by trandolapril or HR 720 may play an important role in preventing the development of atherosclerotic lesions.

Tranilast suppresses vascular chymase expression and neointima formation in balloon-injured dog carotid artery

BACKGROUND

Activation of vascular chymase plays a major role in myointimal hypertrophy after vascular injury by augmenting the production of angiotensin (ANG) II. Because chymase is synthesized mainly in mast cells, we assumed that the chymase-dependent ANG II formation could be downregulated by tranilast, a mast cell-stabilizing antiallergic agent. We have assessed inhibitory effects of tranilast on neointima formation after balloon injury in the carotid artery of dogs, which share a similar ANG II-forming chymase with humans, and further explored the pathophysiological significance of vascular chymase.

METHODS AND RESULTS

Either tranilast (50 mg/kg BID) or vehicle was orally administered to beagles for 2 weeks before and 4 weeks after balloon injury. Four weeks after the injury, remarkable neointima was formed in the carotid arteries of vehicle-treated dogs. Chymase mRNA levels and chymaselike activity of vehicle-treated injured arteries were increased 10.2- and 4.8-fold, respectively, those of uninjured arteries. Angiotensin-converting enzyme (ACE) activity was slightly increased in the injured arteries, whereas ACE mRNA levels were not. Tranilast treatment completely prevented the increase in chymaselike activity, reduced the chymase mRNA levels by 43%, and decreased the carotid intima/media ratio by 63%. In vehicle-treated injured arteries, mast cell count in the adventitia showed a great increase, which was completely prevented by the tranilast treatment. Vascular ACE activity and mRNA levels were unaffected by tranilast.

CONCLUSIONS

Tranilast suppressed chymase gene expression, which was specifically activated in the injured arteries, and prevented neointima formation. Suppression of the chymase-dependent ANG II-forming pathway may contribute to the beneficial effects of tranilast.

Vascular alterations during the development and progression of experimental heart failure

BACKGROUND

Congestive heart failure (HF) is a multifactorial and progressive condition associated with multiple systemic and vascular alterations. The onset and progression of these alterations and the cause of the condition remain undefined. The main purpose of the present study was to help understand the temporal evolution of vascular alterations and their contribution to the pathogenesis of HF. Vascular reactivity to angiotensin II (Ang II) and norepinephrine (NE), as well as circulating and local angiotensin-converting enzyme (ACE) activity, were assessed in the Syrian cardiomyopathic hamster (SCH) model.

METHODS AND RESULTS

We have shown previously that in 2-month-old SCH animals that had not yet developed the clinical manifestations of HF, the contractile response of aortic rings to Ang II was markedly enhanced compared with normal animals. In addition, SCHs showed increased ACE activity in aortic tissue. To assess the relevance of these findings to the development and progression of HF, the temporal evolution of the contractile response of aortic rings to Ang II and NE was evaluated in hamsters at 2, 6, and 11 months of age. Age-matched normal hamsters were used as controls. Within the SCH group, the maximal contraction induced to 10 mumol/L of NE in 2- and 11-month-old animals was similar, but significantly greater than in the age-matched controls (for 2-month-old animals; 1.43 +/- 0.21 g in SCHs v 1.04 +/- 0.15 g in controls; P < .05 and for 11-month-old animals; 1.41 +/- 0.14 g in SCHs v 1.06 +/- 0.07 g in controls; P < .05). The drug concentrations necessary to obtain 50% of the maximal response from the NE concentration-response curves were similar for SCHs and controls at all ages tested. In contrast, the contractility induced by 0.1 mumol/L of Ang II increased progressively in cardiomyopathic animals from 2 to 11 months of age (from 1.3 +/- 0.1 to 1.8 +/- 0.2 g; n = 9; P < .05). In age-matched normal hamsters, the contractile response to Ang II (0.9 +/- 0.1 g) did not vary with age. These findings were observed concomitantly with an increased ACE activity in plasma (18.65 +/- 1.77 nmol/mg x min in controls v 26.5 +/- 1.79 nmol/mg x min in SCHs; P < .05; n = 7) and in heart tissue (0.244 +/- 0.016 nmol/mg x min in controls v 0.563 +/- 0.027 nmol/mg x min in SCHs; P < .05; n = 20) of 11-month-old SCHs.

CONCLUSIONS

These results suggest that, in young animals, increased vascular response to elevated levels of NE and hyperreactivity to Ang II could be critical factors in the development and progression of HF. Indeed, Ang II-induced contractility, as well as plasma and heart ACE activity, are good predictors of the progression and severity of HF.

Kidney aminopeptidase A and hypertension, part I: spontaneously hypertensive rats

Tissue and plasma levels of aminopeptidase A (APA), the principal enzyme that hydrolyzes angiotensin II (Ang II) to angiotensin III, were measured in spontaneously hypertensive rats (SHR) and their normotensive control strain at 3 different ages corresponding to prehypertensive (4 weeks), developing (8 weeks), and established (16 weeks) phases of hypertension. Plasma APA activity was significantly but modestly elevated in SHR at all 3 ages compared with normotensive Wistar-Kyoto rats. Likewise, levels of APA in brain, heart, and adrenal gland were generally, but again only moderately, elevated in SHR at all ages. However, a large increase in APA activity was seen within the kidney in which APA levels were elevated 41%, 51%, and 68% in SHR at 4, 8, and 16 weeks of age, respectively. Kidney APA levels were also significantly increased in immunoblots from 8- and 16-week-old SHR. Glomeruli isolated from 16-week-old SHR had 57% higher APA activity and increased immunoreactivity compared with Wistar-Kyoto rats. To determine whether the increase in kidney APA activity in SHR was related to Ang II levels, SHR were treated for 2 weeks with the angiotensin-converting enzyme inhibitor captopril. Captopril treatment reduced blood pressure to normotensive values and resulted in a 25% reduction in kidney APA activity. These results suggest that APA expression in the kidney may be regulated by activity of the renin-angiotensin system. If so, this would further suggest that upregulation of APA during conditions in which Ang II levels were elevated would have a protective effect against Ang II-mediated cardiovascular diseases, whereas a decrease in APA expression or a failure to upregulate would exacerbate such conditions.

Tissue-localized angiotensin II enhances cardiac and renal disorders in Tsukuba hypertensive mice

OBJECTIVE

To evaluate the relation of tissue-localized angiotensin II (Ang II) concentration with cardiac hypertrophy and glomerulosclerosis in Tsukuba hypertensive mice (THM) carrying both human renin and angiotensinogen genes.

DESIGN

Thirty THM aged 12 weeks were distributed equally to a lisinopril dosage group, a hydralazine dosage group, and an untreated group. Ten age-matched C57BL/6 mice were used as normal controls. Administration was performed for 8 weeks from 12 weeks of age. All mice were euthanized at 20 week of age, and the heart-to-body weight ratio, the renal glomerulosclerosis score, tissue Ang II concentration and tissue catecholamine concentration were measured.

RESULTS

In the untreated group, a significant increase in every examination item was found as compared with that in C57BL/6 mice. In the lisinopril group, the observed value of every item was significantly lower than that in the untreated group. In the hydralazine group, tissue Ang II and catecholamine concentrations and the heart-to-body weight ratio were not different from those in the untreated group. Although the glomerulosclerosis score in the hydralazine group was significantly less than that in the untreated group, this was significantly higher than that in the lisinopril group.

CONCLUSION

Tissue Ang II concentration is more important than hypertension in causing cardiac hypertrophy, and both tissue Ang II level and hypertension are important in causing glomerulosclerosis in THM.

Localization and production of angiotensin II in the isolated perfused rat heart

We used a modification of the isolated perfused rat heart, in which coronary effluent and interstitial transudate were separately collected, to investigate the localization and production of angiotensin II (Ang II) in the heart. During combined renin (0.7 to 1.5 pmol Ang I/mL per minute) and angiotensinogen (6 to 12 pmol/mL) perfusion (4 to 8 mL/min) for 60 minutes (n=3), the steady-state levels of Ang II in interstitial transudate in two consecutive 10-minute periods were 4.3+/-1.5 and 3.6+/-1.5 fmol/mL compared with 1.1+/-0.4 and 1.1+/-0.6 fmol/mL in coronary effluent (mean+/-half range). During perfusion with Ang II (n=5), steady-state Ang II in interstitial transudate was 32+/-19% of arterial Ang II compared with 65+/-16% in coronary effluent (mean+/-SD, P<.02). During perfusion with Ang I (n=5), Ang II in interstitial transudate was 5.1+/-0.6% of arterial Ang I compared with 2.2+/-0.3% in coronary effluent (P<.05). The tissue concentration of Ang II in the combined renin/angiotensinogen perfusions (per gram) was as high as the concentration in interstitial transudate (per milliliter). Addition of losartan (10(-6) mol/L) to the renin/angiotensinogen perfusion (n=3) had no significant effect on the tissue level of Ang II, whereas losartan in the perfusions with Ang I (n=5) or Ang II (n=5) decreased tissue Ang II to undetectably low levels. The results indicate that the heart is capable of producing Ang II and that this can lead to higher levels in tissue than in blood plasma. Cardiac Ang II does not appear to be restricted to the extracellular fluid. This is in part due to AT1-receptor-mediated cellular uptake of extracellular Ang II, but our results also raise the possibility of intracellular Ang II production.

The role of blood pressure and aldosterone in the production of hemorrhagic stroke in captopril-treated hypertensive rats

BACKGROUND AND PURPOSE

We tested the hypothesis that the lowering of plasma aldosterone levels contributed to the antistroke effects of captopril treatment in Wistar Kyoto stroke-prone spontaneously hypertensive rats (SHRSP).

METHODS

The suppression of plasma aldosterone by captopril treatment (50 mg.kg-1.d-1) was prevented by the subcutaneous infusion of aldosterone into captopril-treated SHRSP. We studied the effect this had on blood pressure (BP) and stroke development.

RESULTS

SHRSP fed a Japanese-style diet containing 4% NaCl developed hypertension and a 100% mortality associated with intracerebral hemorrhage by 14 weeks of age. Captopril treatment from 6 weeks of age did not lower the BP but increased survival past 35 weeks of age. Hydralazine treatment (40 to 80 mg/L of drinking water) lowered BP in SHRSP but was less effective than captopril in retarding stroke. Plasma aldosterone levels were elevated with age in SHRSP after 10 weeks and were higher in poststroke versus prestroke SHRSP. Captopril treatment suppressed plasma aldosterone. When we elevated plasma aldosterone in captopril-treated SHRSP to levels between those present in untreated pre- and poststroke SHRSP, the ability of captopril to retard stroke development was negated. The effects of aldosterone were mimicked by deoxycorticosterone (40 mg/kg, SC2 times/wk) but not by dexamethasone (0.1 mg.kg-1.d-1, SC). Spironolactone treatment (20 mg.kg-1.d-1, SC) of SHRSP reduced BP but had little effect on stroke development.

CONCLUSION

Elevations in plasma aldosterone enhance stroke development within captopril-treated SHRSP through mechanisms that do not involve stimulation of mineralocorticoid receptors or the enhancement of hypertension. The antistroke effects of captopril treatment may be partially mediated through the suppression of plasma aldosterone.

Characteristics of diabetes, blood pressure, and cardiac and renal complications in Otsuka Long-Evans Tokushima Fatty rats

To characterize the molecular mechanism of cardiac and renal complications in non-insulin-dependent diabetes mellitus (NIDDM), we examined the gene expression of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a new animal model for human NIDDM, at the ages of 14 weeks (prediabetic stage), 30 weeks (NIDDM stage), and 54 weeks (IDDM stage). Tissue mRNA levels were measured by Northern blot analysis. In 14-week-old OLETF rats, cardiac mRNAs for transforming growth factor-beta1 (TGF-beta1) and extracellular matrix, including collagen types I, III, and IV and laminin, were significantly increased compared with control rats (Long-Evans Tokushima Otsuka rats). Cardiac beta-myosin heavy chain (MHC) mRNA of OLETF was increased at 30 and 54 weeks of age, whereas alpha-MHC mRNA of OLETF was inversely decreased at 54 weeks. Marked perivascular fibrosis was seen in the hearts of OLETF rats from 30 weeks of age. In the kidney of OLETF rats, glomerular TGF-beta1 expression was temporally increased at 30 weeks of age, followed by glomerulosclerosis characterized by mesangial proliferation, thickening of the basement membrane, and nodular lesions. Blood pressure of OLETF rats remained higher than that of control rats from the prediabetic stage to the IDDM stage. Thus, in OLETF rats, cardiac fibrosis-related gene expressions were already enhanced at the prediabetic stage, which supports the involvement of these gene expressions in cardiac perivascular fibrosis. The antithetical change in beta- and alpha-MHC expressions seems to participate in the decreased cardiac contractility seen in diabetes. Furthermore, TGF-beta1 may also contribute to glomerulosclerosis of OLETF rats. OLETF rats seem to be a useful model to study the mechanism of hypertension and cardiac and renal complications in NIDDM.

Vascular aldosterone in genetically hypertensive rats

We have reported that aldosterone is synthesized and cytochrome P450aldo mRNA exists in the vasculature. To clarify the pathophysiological role of vascular aldosterone in hypertension, we compared aldosterone production in the mesenteric arteries of stroke-prone spontaneously hypertensive rats (SHRSP) with that in Wistar-Kyoto rats (WKY). The expressions of mRNA of cytochrome P450aldo, mineralocorticoid receptor, and alpha 1, Na,K-ATPase in the mesenteric arteries were compared between the two groups. Aldosterone concentration in the perfusate of the vasculature was measured by radioimmunoassay after purification with high-performance liquid chromatography. Cytochrome P450aldo and mineralocorticoid receptor mRNA levels were quantified by Southern blot analysis of the products of reverse-transcribed polymerase chain reaction. Levels of alpha 1 Na,K-ATPase mRNA were measured by Northern blot analysis. Vascular aldosterone and cytochrome P450aldo mRNA levels of 2-week-old SHRSP were significantly increased compared with those of age-matched WKY. However, vascular aldosterone in 4- and 9-week-old SHRSP did not differ from that in age-matched WKY. Expression levels of mineralocorticoid receptor mRNA in the vasculature of 4- and 9-week-old SHRSP were significantly increased compared with those in age-matched WKY. Concentrations of vascular alpha 1 Na,K-ATPase mRNA of 2-, 4-, and 9-week-old SHRSP also were significantly higher than those in age-matched WKY. These results suggest that vascular aldosterone contributes to the pathophysiology of hypertension in SHRSP in the early stage.

Contribution of local renin-angiotensin system to cardiac hypertrophy, phenotypic modulation, and remodeling in TGR (mRen2)27 transgenic rats

BACKGROUND

The transgenic rat TGR(mRen2)27, carrying the mouse Ren-2 gene, is a new model to elucidate the role of the local renin-angiotensin system in vivo. However, the role of the local renin-angiotensin system in the heart remains to be determined in TGR(mRen2)27.

METHODS AND RESULTS

TGR(mRen2)27 were treated with various antihypertensive drugs for 6 weeks to examine the effects on cardiac hypertrophy and gene expression. Cardiac mRNAs were examined by Northern blot analysis. In TGR(mRen2)27, left ventricular hypertrophy was associated with a decrease in alpha-myosin heavy chain expression of 31% and an increase in skeletal alpha-actin and atrial natriuretic polypeptide expression by 2.6- and 21-fold, respectively (P < .05), thereby showing the shift of myocardium to a fetal phenotype. Furthermore, cardiac collagen and laminin expressions were increased in TGR(mRen2)27 (P < .05), suggesting the occurrence of cardiac remodeling. Although treatment of TGR(mRen2)27 with a high dose of TCV-116 (angiotensin AT1 receptor antagonist) or manidipine (calcium antagonist) combined with atenolol (beta 1-adrenergic receptor blocker) completely normalized blood pressure, TCV-116 regressed cardiac hypertrophy and suppressed the changes in cardiac mRNA levels of TGR(mRen2)27 much more potently than manidipine with atenolol. Furthermore, the inhibitory effects of a low dose of TCV-116 on cardiac hypertrophy and altered gene expressions of TGR(mRen2)27 were greater than those of doxazosin (alpha 1-adrenergic receptor blocker) combined with atenolol, despite their similar hypotensive effects.

CONCLUSIONS

Our present observations provide evidence that the cardiac renin-angiotensin system in TGR(mRen2)27 is responsible for cardiac hypertrophy, phenotypic modulation, and remodeling.

Tissue-specific regulation of angiotensinogen gene expression in spontaneously hypertensive rats

Angiotensinogen is expressed in many tissues besides the liver. Recent studies have suggested that abnormalities in the regulation of angiotensinogen gene expression may be involved in the development of hypertension. However, little information is available concerning the functional significance of tissue angiotensinogen. In this study, we measured plasma angiotensinogen concentration by radioimmunoassay and examined the expression of tissue angiotensinogen by Northern blot analysis in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Although plasma angiotensinogen concentration in SHR was comparable to that in WKY at 6 weeks of age, it was increased significantly at 14 weeks of age in SHR and became higher than that in WKY. The levels of hepatic angiotensinogen mRNA were similar in SHR and WKY, and the levels of aortic, adrenal, and renal angiotensinogen mRNAs were lower in SHR than in WKY at both 6 and 14 weeks of age. Brain angiotensinogen expression in SHR was higher than in WKY at 6 weeks of age and was comparable to that in WKY at 14 weeks of age. On the other hand, cardiac and fat angiotensinogen mRNA levels were significantly increased at 14 weeks of age in SHR. These results demonstrate that the expression of tissue angiotensinogen is regulated differently in SHR and WKY and indicate that the development of hypertension is accompanied at least temporally with increases in plasma angiotensinogen concentration as well as cardiac and adipogenic angiotensinogen mRNA in SHR.

Genetic analysis of renin gene expression in rat adrenal gland

We examined the mechanism of the increased renin mRNA concentration in the adrenal glands of spontaneously hypertensive rats (SHR). In 52 female F2 rats (25 to 27 weeks of age) derived from SHR and Wistar-Kyoto rats, we determined blood pressure, renin mRNA concentration in the adrenal gland, plasma renin activity, plasma aldosterone concentration, and genotype of the renin gene. Eighteen of the F2 rats were fed a high salt (8%) diet for 14 days. The renin mRNA concentration in the adrenal glands showed a significant correlation with the genotype of the renin gene in the normal salt diet group (P <.0001), whereas this relationship was not observed in the high salt group. Multivariate analysis revealed that the plasma aldosterone concentration in the normal diet group was significantly explained (P=.0004, R2=.454) by plasma renin activity (P=.0005), the renin mRNA concentration in the adrenal gland (P=.0496), and the genotype of the renin gene (P=.0236). The SHR allele of the renin gene was associated with a lower aldosterone concentration. On the other hand, in the high salt diet group, only the genotype of the renin gene showed a significant relationship with plasma aldosterone concentration (P=.0237). Again, the SHR allele of the renin gene was associated with a lower aldosterone concentration. We can conclude that the higher renin mRNA concentration in the SHR adrenal glands is governed by the SHR allele of the renin gene or renin gene locus. The renin mRNA concentration in the adrenal gland exerts a minor influence on aldosterone synthesis. Paradoxically, the SHR allele of the renin gene or renin gene locus confers a lower rate of aldosterone synthesis at 25 to 27 weeks of age, the mechanism of which remains to be determined.

Urinary excretion of 19-noraldosterone in the spontaneously hypertensive rat and stroke-prone spontaneously hypertensive rat

1. We measured the urinary excretion of 19-noraldosterone in the spontaneously hypertensive rat (SHR) and stroke-prone SHR (SHRSP) during the development of hypertension and compared these measurements with Wistar-Kyoto (WKY) rats. 2. 19-Noraldosterone in rat urine was confirmed using HPLC-MS. Urine samples were collected from 4 and 9 week old SHR (n = 12), SHRSP (n = 12) and WKY rats (n = 9). 19-Noraldosterone was measured by specific radio immunoassay after purification of the urine extracts with HPLC. 3. There were no significant differences in plasma corticosterone among SHR, SHRSP and WKY rats at 4 and 9 weeks of age. Aldosterone levels were increased in the prehypertensive SHR and SHRSP. Nine week old SHRSP showed high plasma concentration of aldosterone compared with SHR or WKY rats of the same age. 4. Urinary excretion of 19-noraldosterone was increased in 4 week old SHR (15 +/- 4.2 pmol/day) and SHRSP (17 +/- 5.0 pmol/day) compared with WKY rats (9 +/- 3.9 pmol/day) at the same age. Nine week old SHR showed decreased urinary excretion of 19-noraldosterone compared with WKY rats at the same age. Urinary levels of 19-noraldosterone were higher in SHRSP (11 +/- 4.9 pmol/day) than in SHR (7 +/- 4.0 pmol/day) at 9 weeks of age. 5. Adrenal mineralocorticoids are suggested to be responsible for the abnormal vascular reactivity observed in SHRSP. Relatively elevated levels of 19-noraldosterone in SHRSP may contribute to malignant hypertension in this model.

Differential gene expression of renin and angiotensinogen in the TGR(mREN-2)27 transgenic rat

Transgenic rats carrying the murine Ren-2 gene represent a monogenetic model of hypertension characterized by low plasma renin and high extrarenal expression of the transgene. The hypothesis has been raised that stimulated local reninangiotensin systems may be responsible for the development of hypertension in this model. This study analyzes the effects of the converting enzyme inhibitor lisinopril, which specifically interferes with the renin-angiotensin system, and the direct vasodilator dihydralazine on the renal and extrarenal expression of renin and angiotensinogen. A comparison of gene expression between heterozygous and homozygous transgenic and normal Sprague-Dawley rats was also performed. We demonstrate high sensitivity of blood pressure toward converting enzyme inhibition in transgenic TGR(mREN-2)27 rats. In the kidney, expression of the transgene and the endogenous renin gene increased, suggesting that both are modulated by lisinopril in a similar manner. On the other hand, blood pressure reduction by dihydralazine did not abolish renal renin suppression in transgenic rats, indicating that mechanisms different from direct effects of blood pressure account for renin suppression. Homozygosity for the transgene led to increased Ren-2 expression and higher blood pressure and had opposite effects on angiotensinogen expression compared with heterozygous rats. Cardiac hypertrophy was reduced by lisinopril but not dihydralazine and was positively correlated with cardiac angiotensinogen expression. Increased angiotensin II in the adrenal gland of TGR(mREN-2)27 rats, which overexpresses the transgene, provides evidence that this leads to enhanced generation of tissue angiotensin II. We conclude that expression of the mouse transgene, the endogenous rat renin gene, and the angiotensinogen gene is subject to differential tissue-specific regulation. Reversal of cardiovascular damage with the converting enzyme inhibitor but not dihydralazine suggests that angiotensin II generated locally may be involved in the pathogenesis of hypertension and structural changes in TGR(mREN-2)27 rats.

Effects of kidney transplantation on the renin-angiotensin systems of the recipients

To investigate the effects of renal transplantation on the plasma and local kidney renin-angiotensin systems of the recipients the left kidneys of 13 adult male Wistar-Kyoto rats (WKY) and 13 stroke-prone spontaneously hypertensive rats (SHRSP) were transplanted to bilaterally nephrectomized (WKYxSHRSP)-F1 hybrids. Nine unilaterally nephrectomized WKY and nine SHRSP served as controls. Four weeks after surgery recipients of an SHRSP kidney but not recipients of a WKY kidney had significant post-transplantation hypertension. Plasma renin activity (PRA) was higher in SHRSP than in WKY. Transplanted rats had lower PRAs than nontransplanted controls. Plasma ACE activity was lowest in SHRSP, intermediate in transplanted F1 hybrids and highest in WKY. Plasma Ang I and Ang II concentrations closely paralleled each other. They were not significantly different between WKY and SHRSP and lower in transplanted than in nontransplanted rats. ACE and renin mRNA were lower in transplanted than in nontransplanted kidneys. Glomerular angiotensin II receptor density was higher in transplanted than in nontransplanted kidneys with no significant differences between strains. We conclude that renal transplantation has profound long-term effects on the recipients' plasma and local kidney renin-angiotensin systems. These do not appear to be involved in the pathogenesis of post-transplantation hypertension in recipients of an SHRSP kidney, but may reflect a role for the intrarenal renin-angiotensin system in long-term renal adaptation and repair processes after transplantation.

Contribution of renal angiotensin II type I receptor to gene expressions in hypertension-induced renal injury

Recent evidence indicates that transforming growth factor-beta 1 (TGF-beta 1) plays an important role in renal fibrosis via stimulation of extracellular matrix synthesis. The present study was undertaken to investigate the role of angiotensin II type I receptor (AT1 receptor) in hypertension-induced renal injury. Twenty-two-week-old stroke-prone spontaneously hypertensive rats (SHRSP), which had established hypertension and moderate renal damage, were orally given TCV-116, a selective non-peptide AT1 receptor antagonist (0.1, 1 or 10 mg/kg/day), enalapril (10 mg/kg/day) or vehicle once a day for 10 weeks. At the end point of the treatment, we examined renal function, the gene expressions of TGF-beta 1 and extracellular matrix components in the interstitium [collagen types I (COI) and III (COIII), fibronectin (FN)] and the basement membrane (COIV and laminin), and renal microscopic morphology in rats aged 32 weeks. In vehicle-treated 32 week-old SHRSP with renal dysfunction and nephrosclerosis, renal mRNA levels for TGF-beta 1, COI, COIII, FN, COIV were all several-fold higher than in WKY. Thus, renal TGF-beta 1 gene expression was enhanced in SHRSP, which may contribute to the increased renal expressions of COI, COIII, FN, COIV in SHRSP. Treatment with TCV-116 (0.1 mg/kg/day) in SHRSP, in spite of no reduction of blood pressure, decreased renal mRNA levels for TGF-beta 1, COI, COIII, FN, COIV, being accompanied by the significant decrease in urinary protein and albumin excretion, blood urea nitrogen and plasma creatinine. Treatment with TCV-116 (10 mg/kg/day) in SHRSP decreased mRNAs for TGF-beta 1, COI, COIII, FN and COIV to almost the same levels as WKY, being associated with normalization of urinary protein and albumin excretion and the prevention of nephrosclerosis, as judged by microscopic histological observations. On the other hand, the effects of enalapril (10 mg/kg/day) on the above mentioned mRNA levels, renal function and renal morphology were weaker than those of TCV-116 (10 mg/kg/day) and were as much as TCV-116 (1 mg/kg/day). These results suggest that independently of hypotensive action, AT1 receptor antagonist has a potent renal protective effect by inhibiting the gene expression of renal TGF-beta 1 and extracellular matrix components.

Role of angiotensin II in renal injury of deoxycorticosterone acetate-salt hypertensive rats

To investigate the role of angiotensin II (Ang II) in hypertension-induced tissue injury, we gave TCV-116 (1 mg/kg per day PO), a nonpeptide Ang II type I receptor antagonist, or enalapril (10 mg/kg per day PO) to deoxycorticosterone acetate (DOCA)-salt hypertensive rats for 3 weeks and examined the effects on tissue mRNA levels for transforming growth factor-beta 1 (TGF-beta 1) and extracellular matrix components. Tissue mRNA levels were measured by Northern blot analysis. Renal mRNA levels for TGF-beta 1; types I, III, and IV collagen; and fibronectin in DOCA-salt hypertensive rats were increased by severalfold (P < .01) compared with sham-operated rats. In the aorta of DOCA-salt hypertensive rats, TGF-beta 1 and fibronectin mRNA levels were increased, but types I, III, and IV collagen mRNAs did not increase. In the heart, increased mRNA was found only for fibronectin. Thus, these gene expressions are regulated in a tissue-specific manner. TCV-116 or enalapril did not lower blood pressure in DOCA-salt hypertensive rats. However, the increase in renal mRNAs for TGF-beta 1 and extracellular matrix components in DOCA-salt hypertensive rats was significantly inhibited by treatment with TCV-116 or enalapril, which was associated with a significant decrease in urinary protein and albumin excretions and histological improvement of renal lesions. In contrast, in the aorta and heart these gene expressions were not affected by TCV-116 or enalapril. Thus, local Ang II may contribute to renal injury of DOCA-salt hypertension by stimulating the gene expression of TGF-beta 1 and extracellular matrix components.

Cardiac renin and angiotensins. Uptake from plasma versus in situ synthesis

The existence of a cardiac renin-angiotensin system, independent of the circulating renin-angiotensin system, is still controversial. We compared the tissue levels of renin-angiotensin system components in the heart with the levels in blood plasma in healthy pigs and 30 hours after nephrectomy. Angiotensin I (Ang I)-generating activity of cardiac tissue was identified as renin by its inhibition with a specific active site-directed renin inhibitor. We took precautions to prevent the ex vivo generation and breakdown of cardiac angiotensins and made appropriate corrections for any losses of intact Ang I and II during extraction and assay. Tissue levels of renin (n = 11) and Ang I (n = 7) and II (n = 7) in the left and right atria were higher than in the corresponding ventricles (P < .05). Cardiac renin and Ang I levels (expressed per gram wet weight) were similar to the plasma levels, and Ang II in cardiac tissue was higher than in plasma (P < .05). The presence of these renin-angiotensin system components in cardiac tissue therefore cannot be accounted for by trapped plasma or simple diffusion from plasma into the interstitial fluid. Angiotensinogen levels (n = 11) in cardiac tissue were 10% to 25% of the levels in plasma, which is compatible with its diffusion from plasma into the interstitium. Like angiotensin-converting enzyme, renin was enriched in a purified cardiac membrane fraction prepared from left ventricular tissue, as compared with crude homogenate, and 12 +/- 3% (mean +/- SD, n = 6) of renin in crude homogenate was found in the cardiac membrane fraction and could be solubilized with 1% Triton X-100. Tissue levels of renin and Ang I and II in the atria and ventricles were directly correlated with plasma levels (P < .05), and in both tissue and plasma the levels were undetectably low after nephrectomy. We conclude that most if not all renin in cardiac tissue originates from the kidney. Results support the contentions that in the healthy heart, angiotensin production depends on plasma-derived renin and that plasma-derived angiotensinogen in the interstitial fluid is a potential source of cardiac angiotensins. Binding of renin to cardiac membranes may be part of a mechanism by which renin is taken up from plasma.

Effect of an angiotensin II receptor antagonist, CV-11974, and its prodrug, TCV-116, on production of aldosterone

In dispersed rabbit adrenocortical glomerulosa cells, a non-peptide angiotensin II (AT1) receptor antagonist, CV-11974 (10(-10)-10(-5) M), competitively inhibited angiotensin II- or angiotensin III-stimulated aldosterone production, whereas PD123177, an angiotensin AT2 receptor antagonist, did not. CV-11974 inhibited aldosterone production induced by 4 mM K+ but not by 12 mM K+. CV-11974 had no effect on adrenocorticotropic hormone-stimulated aldosterone or corticosterone production, but inhibited angiotensin II-stimulated corticosterone production. In the rat, TCV-116, the prodrug of CV-11974, (0.1 and 1 mg/kg, p.o.) markedly reduced the elevation of both plasma aldosterone concentration and blood pressure induced by i.v. infusion of angiotensin II. In spontaneously hypertensive rats, TCV-116 at daily p.o. doses of 0.1, 1 and 10 mg/kg for 2 weeks caused a dose-dependent reduction of blood pressure and plasma aldosterone concentration without affecting plasma corticosterone. Thus, TCV-116 inhibited the induction of aldosterone production by not only exogenous but also endogenous angiotensin II.

Nephrectomy, converting enzyme inhibition, and angiotensin peptides

To determine the contribution of kidney-derived renin and angiotensin converting enzyme to circulating and tissue levels of angiotensin peptides, we measured angiotensin (Ang)-(1-7), Ang II, Ang-(1-9), and Ang I in plasma, kidney, lung, heart, aorta, brown adipose tissue, adrenal, pituitary, and brain of five groups of male Sprague-Dawley rats: control rats, rats given the converting enzyme inhibitor ramipril (10 mg/kg), rats nephrectomized 24 hours, rats nephrectomized 48 hours, and rats nephrectomized 48 hours and given ramipril. Plasma and tissues, apart from adrenal, showed a 63% to 98% reduction in Ang II, the ratio of Ang II to Ang I, or both after ramipril administration, indicating a major role for converting enzyme in Ang II formation. Nephrectomy caused a more than 95% decrease in plasma renin levels and a fourfold to eightfold increase in plasma angiotensinogen levels. Apart from plasma and brain, tissues showed a 59% to 78% decrease in Ang II levels after nephrectomy, indicating a major role for kidney-derived renin in Ang II formation. The persistence of Ang II in plasma and tissues of anephric rats indicates that Ang II may be formed by a process independent of kidney-derived renin; this process may be amplified by the increased plasma angiotensinogen levels that accompany nephrectomy. For lung, adrenal, and aorta, Ang II levels showed a further decrease when nephrectomized rats were given ramipril. However, for plasma and the other tissues, ramipril produced little or no decrease in Ang II levels of anephric rats, suggesting that Ang II may be formed by a pathway independent of converting enzyme. Such a pathway may involve the direct formation of Ang II from angiotensinogen by a non-renin-like enzyme.

Chromosome 17q23: a locus for cardiovascular disease

1. The gene for dipeptidyl carboxypeptidase 1 (angiotensin I-converting enzyme, kininase II; DCP1), located on chromosome 17q23, has been implicated in hypertension in rats. In humans associations have been found for the insertion allele of a bi-allelic insertion/deletion polymorphism of DCP1 with hypertension and the deletion allele with myocardial infarction. Other hypertension studies have, however, failed to find a relationship. 2. Mathematical predictions based on DCP1 association data suggest that high sib-pair numbers may be needed to achieve statistical significance by this approach, although differences in the severity of hypertension in different study groups could account for the disparate findings. 3. No association was found between DCP1 allele or genotype frequencies and obesity in essential hypertensives.