Captopril reduces aortic and microvascular growth in hypertensive and normotensive rats

Effect of captopril on post-infarction remodelling visualized by light sheet microscopy and echocardiography

Angiotensin converting enzyme inhibitors, among them captopril, improve survival following myocardial infarction (MI). The mechanisms of captopril action remain inadequately understood due to its diverse effects on multiple signalling pathways at different time periods following MI. Here we aimed to establish the role of captopril in late-stage post-MI remodelling. Left anterior descending artery (LAD) ligation or sham surgery was carried out in male C57BL/6J mice. Seven days post-surgery LAD ligated mice were allocated to daily vehicle or captopril treatment continued over four weeks. To provide comprehensive characterization of the changes in mouse heart following MI a 3D light sheet imaging method was established together with automated image analysis workflow. The combination of echocardiography and light sheet imaging enabled to assess cardiac function and the underlying morphological changes. We show that delayed captopril treatment does not affect infarct size but prevents left ventricle dilation and hypertrophy, resulting in improved ejection fraction. Quantification of lectin perfused blood vessels showed improved vascular density in the infarct border zone in captopril treated mice in comparison to vehicle dosed control mice. These results validate the applicability of combined echocardiographic and light sheet assessment of drug mode of action in preclinical cardiovascular research.

Microvascular disease in chronic kidney disease: the base of the iceberg in cardiovascular comorbidity

Chronic kidney disease (CKD) is a relentlessly progressive disease with a very high mortality mainly due to cardiovascular complications. Endothelial dysfunction is well documented in CKD and permanent loss of endothelial homeostasis leads to progressive organ damage. Most of the vast endothelial surface area is part of the microcirculation, but most research in CKD-related cardiovascular disease (CVD) has been devoted to macrovascular complications. We have reviewed all publications evaluating structure and function of the microcirculation in humans with CKD and animals with experimental CKD. Microvascular rarefaction, defined as a loss of perfused microvessels resulting in a significant decrease in microvascular density, is a quintessential finding in these studies. The median microvascular density was reduced by 29% in skeletal muscle and 24% in the heart in animal models of CKD and by 32% in human biopsy, autopsy and imaging studies. CKD induces rarefaction due to the loss of coherent vessel systems distal to the level of smaller arterioles, generating a typical heterogeneous pattern with avascular patches, resulting in a dysfunctional endothelium with diminished perfusion, shunting and tissue hypoxia. Endothelial cell apoptosis, hypertension, multiple metabolic, endocrine and immune disturbances of the uremic milieu and specifically, a dysregulated angiogenesis, all contribute to the multifactorial pathogenesis. By setting the stage for the development of tissue fibrosis and end organ failure, microvascular rarefaction is a principal pathogenic factor in the development of severe organ dysfunction in CKD patients, especially CVD, cerebrovascular dysfunction, muscular atrophy, cachexia, and progression of kidney disease. Treatment strategies for microvascular disease are urgently needed.

Salt, Angiotensin II, Superoxide, and Endothelial Function

Proper function of the vascular endothelium is essential for cardiovascular health, in large part due to its antiproliferative, antihypertrophic, and anti-inflammatory properties. Crucial to the protective role of the endothelium is the production and liberation of nitric oxide (NO), which not only acts as a potent vasodilator, but also reduces levels of reactive oxygen species, including superoxide anion (O2•-). Superoxide anion is highly injurious to the vasculature because it not only scavenges NO molecules, but has other damaging effects, including direct oxidative disruption of normal signaling mechanisms in the endothelium and vascular smooth muscle cells. The renin-angiotensin system plays a crucial role in the maintenance of normal blood pressure. This function is mediated via the peptide hormone angiotensin II (ANG II), which maintains normal blood volume by regulating Na+ excretion. However, elevation of ANG II above normal levels increases O2•- production, promotes oxidative stress and endothelial dysfunction, and plays a major role in multiple disease conditions. Elevated dietary salt intake also leads to oxidant stress and endothelial dysfunction, but these occur in the face of salt-induced ANG II suppression and reduced levels of circulating ANG II. While the effects of abnormally high levels of ANG II have been extensively studied, far less is known regarding the mechanisms of oxidant stress and endothelial dysfunction occurring in response to chronic exposure to abnormally low levels of ANG II. The current article focuses on the mechanisms and consequences of this less well understood relationship among salt, superoxide, and endothelial function.

Renal medullary (pro)renin receptor contributes to angiotensin II-induced hypertension in rats via activation of the local renin-angiotensin system

BACKGROUND

(Pro)renin receptor (PRR) is a new component of the renin-angiotensin system and regulates renin activity in vitro. Within the kidney, PRR is highly expressed in the renal medulla where its expression is induced by angiotensin II infusion. The objective of the present study was to test a potential role of renal medullary PRR during angiotensin II-induced hypertension.

METHODS

A rat AngII infusion model (100 ng/kg/min) combined with renal intramedullary infusion of PRO20, a specific inhibitor of PRR, was builded. And the intravenous PRO20 infusion serve as control. Mean arterial pressure was recorded by radiotelemetry for one week. Further analysis of kidney injury, inflammation, biochemical indices and protein localization were performed in vivo or in vitro.

RESULTS

Radiotelemetry demonstrated that AngII infusion elevated the mean arteria pressure from 108 ± 5.8 to 164.7 ± 6.2 mmHg. Mean arterial pressure decreased to 128.6 ± 5.8 mmHg (P < 0.05) after intramedullary infusion of PRO20, but was only modestly affected by intravenous PRO20 infusion. Indices of kidney injury, including proteinuria, glomerulosclerosis, and interstitial fibrosis, inflammation, and increased renal medullary and urinary renin activity following angiotensin II infusion were all remarkably attenuated by intramedullary PRO20 infusion. Following one week of angiotensin II infusion, increased PRR immunoreactivity was found in vascular smooth muscle cells. In cultured rat vascular smooth muscle cells, angiotensin II induced parallel increases in soluble PRR and renin activity, and the latter was significantly reduced by PRO20.

CONCLUSION

Renal medullary PRR mediates angiotensin II-induced hypertension, likely by amplifying the local renin response.

Evaluation of polyherbal formulation (SJT-HT-03) for antihypertensive activity in albino rats

BACKGROUND

Hypertension is an incurable pathological condition and lifelong therapy is required. Long term use of conventional synthetic anti-hypertensive drugs is associated with a spectrum of toxic effects. However, therapeutic interventions using herbal drugs for hypertension have gained considerable attention worldwide.

AIM

To evaluate the anti-hypertensive activity of polyherbal formulation (SJT-HT-03).

MATERIALS AND METHODS

The polyherbal formulation (SJT-HT-03) comprises of leaves of Aegle marmelos L., fruits of Benincasa hispida Thunb., Garcinia indica Thouars, and flowers of Musa paradiasica L., Rosa indica L., Hibiscus rosa sinensis L. Selected plants as mentioned above were collected, dried and extracted with different solvents. Formulation SJT-HT-03 (250 mg/kg, p.o.), was evaluated using two kidney one clip (2K1C) model and deoxycorticosterone acetate (DOCA)-salt-induced hypertension model using the enalapril (10 mg/kg, p.o.) and hydrochlorothiazide (5 mg/kg, p.o.) as a reference standard drug in respective models.

RESULTS

SJT-HT-03 significantly reduced (P < 0.001, one-way analysis of variance followed by Turkey's multiple comparison tests) systolic as well as diastolic blood pressure (BP) in 2K1C and DOCA-salt model. Further, SJT-HT-03 has shown a significant reduction (P < 0.01) in angiotensin converting enzyme (ACE) activity in serum, clipped kidney as well as in lungs in 2K1C model, whereas significant reduction (P < 0.05) in serum Na(+) and increase in serum K(+) level in DOCA model.

CONCLUSION

Polyherbal formulation SJT-HT-03 possess significant anti-hypertensive activity by producing direct depressant effect on heart, inhibition of ACE, aldosterone antagonistic as well as diuretic effect and thereby act on multiple targets to achieve optimal effect.

Aortic remodelling following the treatment and regression of hypertensive left ventricular hypertrophy: a cardiovascular magnetic resonance study

BACKGROUND

Increased arterial stiffness independently predicts adverse prognosis. While different antihypertensive strategies produce different magnitudes of left ventricular hypertrophy (LVH) regression, there are no comparative data on how these strategies affect arterial stiffness. The aim was to determine the longitudinal change in aortic stiffness following the treatment of essential hypertension with two mechanistically different antihypertensive treatment strategies.

METHODS AND RESULTS

Forty-two patients with essential hypertension and CMR confirmed with LVH were randomly assigned to antihypertensive regimes for 6 months. Treatment strategies were designed either to inhibit the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS) (valsartan and moxonidine, group VM) or to have neutral effect on these systems (bendroflumethiazide and amlodipine, group BA). Both treatment groups underwent identical baseline and a 6-month follow-up CMR and were compared with a healthy age-matched control group. Baseline aortic distensibility (AD) was lower in both hypertensive groups compared with controls (2.8 × 10(-3 )mmHg(-1) in group VM (p = 0.001) and 3.3 × 10(-3 )mmHg(-1) group BA (p = 0.039) compared with 4.5 × 10(-3 )mmHg(-1) in the control group). AD increased after antihypertensive therapy (VM: 2.8 × 10(-3 )mmHg(-1)-4.2 × 10(-3 )mmHg(-1) (p = 0.001); BA 3.3 × 10(-3 )mmHg(-1)-4.6 × 10(-3 )mmHg(-1) (p < 0.01)). In both treatment groups AD returned to a level comparable with the normal control group (p = 0.81) after 6 months.

CONCLUSIONS

In patients with essential hypertension and LVH, AD was lower than in matched normal controls. Despite the opposing pharmacological mechanisms utilised across the treatment groups, the improvement in AD was similar, suggesting that blood pressure reduction per se may be more important than RAAS and SNS inhibition for the improvement of aortic remodelling.

N-acetyl-seryl-aspartyl-lysyl-proline attenuates renal injury and dysfunction in hypertensive rats with reduced renal mass: council for high blood pressure research

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a naturally occurring peptide of which the plasma concentration is increased 4- to 5-fold by angiotensin-converting enzyme inhibitors. We reported previously that, in models of both hypertension and postmyocardial infarction, Ac-SDKP reduces cardiac inflammation and fibrosis. However, it is unknown whether Ac-SDKP can prevent or reverse renal injury and dysfunction in hypertension. In the present study, we tested the hypothesis that, in rats with 5/6 nephrectomy (5/6Nx)-induced hypertension, Ac-SDKP reduces renal damage, albuminuria, and dysfunction by decreasing inflammatory cell infiltration and renal fibrosis and by increasing nephrin protein. Ac-SDKP (800 microg/kg per day, SC via osmotic minipump) or vehicle was either started 7 days before 5/6Nx (prevention) and continued for 3 weeks or started 3 weeks after 5/6Nx (reversal) and continued for another 3 weeks. Rats with 5/6Nx developed high blood pressure, left ventricular hypertrophy, albuminuria, decreased glomerular filtration rate, and increased macrophage infiltration (inflammation) and renal collagen content (fibrosis). Ac-SDKP did not affect blood pressure or left ventricular hypertrophy in either group; however, it significantly reduced albuminuria, renal inflammation, and fibrosis and improved glomerular filtration rate in both prevention and reversal groups. Moreover, slit diaphragm nephrin protein expression in the glomerular filtration barrier was significantly decreased in hypertensive rats. This effect was partially prevented or reversed by Ac-SDKP. We concluded that Ac-SDKP greatly attenuates albuminuria and renal fibrosis and improves renal function in rats with 5/6Nx. These effects may be related to decreased inflammation (macrophages) and increased nephrin protein.

Effects of angiotensin-converting enzyme inhibitor and exercise training on exercise capacity and skeletal muscle

OBJECTIVE

Physical fitness is closely related with cardiovascular health. We examined the effects of angiotensin-converting enzyme inhibitor, exercise training and their combination on exercise capacity as well as skeletal muscle fiber type and capillarity in spontaneously hypertensive rats (SHR).

METHODS

Seven-week-old male SHR were allocated to four groups: sedentary control (C), treatment with perindopril (3 mg/kg per day) (Per), exercise training on a treadmill (EX), and their combination (Per + EX). Following 8-week interventions, rats were submitted to a stepwise exercise test on a treadmill. After experiments, fiber type and capillarity in soleus muscle were examined.

RESULTS

Exercise capacity significantly increased in Per compared with in C. Combination of exercise training and perindopril further increased exercise capacity compared with perindopril alone, whereas there was no significant difference in exercise capacity between EX and Per + EX. Capillary density increased similarly in Per and EX compared with in C. Combination of exercise training and perindopril further increased capillary density compared with exercise training alone. The percentage of type I fiber increased only in Per + EX.

CONCLUSIONS

We found that in growing SHR, chronic treatment with perindopril enhances untrained exercise capacity, while it does not affect acquired exercise capacity as a result of exercise training. We also found that perindopril promotes adaptive changes of skeletal muscle in response to exercise such as increases in capillary density and percentage of type I fiber.

Angiotensin II Captopril Cotreatment Augments Angiogenesis in Abdominal Skin Flap in Rats

The effect of captopril, angiotensin-converting enzyme inhibitor, on angiogenesis in several reports remained unclear. Its effect on neovascularization in rat abdominal skin flaps was investigated. Flap elevation, based on the right superficial inferior epigastric artery was performed with or without the administration of captopril (10 mg/kg/d), Ang II (100 microg/kg/d), or captopril and Ang II cotreatment. Mean arterial pressure (MAP), microangiography, capillary density measurement, necrosis area determination, laser Doppler flowmetry (LDF), AT1 and vascular endothelial growth factor (VEGF) immunostaining were used to evaluate the effects of captopril and the interaction between captopril and Ang II on the angiogenesis. Ang II and captopril cotreatment improved angiogenesis more than Ang II or captopril alone. The reduction of necrosis, enhancement of vascular network formation, capillary density, VEGF immunostaining, and local blood flow were evident in the cotreated group. We suggest that Ang II and captopril cotreatment improves ischemia-induced angiogenesis and increased viability and vascularity of skin flap in rats.

Attenuated vasoconstrictor responses to endothelin in afferent arterioles during a high-salt diet

Endothelin-1 (ET-1) is increased in rats on a high-salt (HS) diet and participates in salt-dependent hypertension. Afferent arterioles (AA) are important for long-term blood pressure control, and therefore we hypothesized that a HS diet would alter their responsiveness to ET-1. Sprague-Dawley rats were fed either a normal-salt (NS; 0.66% NaCl) or HS (8%) diet for 1 wk. Diameters of AA were determined in response to increasing concentrations of big ET-1, ET-1, sarafotoxin 6c (S6c), or norepinephrine (NE), using the blood-perfused juxtamedullary nephron technique. ET-1 responses were also determined during blockade of endothelin type A (ETA) or type B (ETB) receptors with 10 nM ABT-627 or 30 nM A-192621, respectively. Expression of ETA and ETB receptors was determined in renal microvessels. Responses of AA to big ET-1, ET-1, and S6c were significantly attenuated during a HS diet (e.g., response to 10−10 M ET-1 in NS vs. HS rats: −52.5 ± 10.2 vs. +5.6 ± 11.3% of control diameter; P < 0.05), with no change in the responses to NE. ETB, but not ETA receptor blockade abolished the different response to ET-1 between the NS and HS groups. ETB receptor expression in renal microvessels was increased in response to HS (17.7 ± 2.4 vs. 6.6 ± 3.0% of β-actin, P = 0.02), whereas ETA receptor expression was unchanged. These results suggest that the reduced vasoconstrictor response of AA to endothelin peptides during a HS diet is mediated by increased vasodilatory function of endothelial ETB receptors. By preserving renal blood flow, this may be an important mechanism to restore sodium balance during a HS diet.

Angiotensin II-induced growth of vascular smooth muscle cells is associated with modulation of cell surface area and platelet-derived growth factor receptor expression

1. Excessive growth of vascular smooth muscle cells (VSMC) can lead to critical problems in the treatment of some vascular diseases. Recent studies suggest a connection between this abnormal growth of VSMC and the octapeptide hormone angiotensin (Ang) II. However, the growth-promotive potential of AngII on VSMC is unclear. 2. Using the novel AngII inhibitor E4177 and an original animal model, we confirmed that AngII does function in abnormal growth of VSMC induced after transplantation of vein grafts in an animal model. 3. Furthermore, using a primary culture of human aortic smooth muscle cells (HASMC), we found that AngII augmented the growth of HASMC in a serum-dependent manner and induced enlargement of the cell surface area in HASMC, both effects being nullified by E4177. The latter effect of AngII was associated with an increase in the expression level of platelet-derived growth factor (PDGF) receptors. In specimens obtained from the animal model, PDGF receptors were highly expressed. 4. These data obtained in vitro and in vivo imply that AngII has the potential to promote growth of VSMC and suggest that this growth promotion may be mediated by enlargement of the cell surface area.

Effects of oestrogen treatment and angiotensin-converting enzyme inhibition on the microvasculature of ovariectomized spontaneously hypertensive rats

We investigated the role of oestrogen in the function and structure of the microcirculation of female spontaneously hypertensive rats (SHRs), and evaluated the effect of 17beta-oestradiol on their cardiovascular response to pharmacological agents that block the formation of angiotensin II. Ten-week-old SHRs were randomly assigned to the following groups: intact, ovariectomized, and ovariectomized treated with 17beta-oestradiol (1.5 mg delivered over 60 days) and/or captopril (5 mg kg(-1) day(-1) for 8 weeks). Systolic blood pressure was determined from the time of ovariectomy up to 18 weeks of age, at which time endothelial function and microvascular density in skeletal muscle were evaluated. Both 17beta-oestradiol and captopril prevented development of hypertension in ovariectomized rats. Furthermore, coadministration of both drugs had a greater antihypertensive effect than either one alone. Acetylcholine-induced vasodilatation was impaired in ovariectomized SHRs, and the response was improved by treatment with 17beta-oestradiol and/or captopril. In addition, 17beta-oestradiol replacement in ovariectomized rats enhanced the effect of captopril on acetylcholine-induced vasodilatation. Ovariectomized rats also showed lower microvascular density than intact rats, an effect that was prevented by 17beta-oestradiol replacement or captopril treatment and, to a significantly larger extent, by coadministration of both. We concluded that both 17beta-oestradiol and captopril attenuated the development of hypertension and improved the impairment in microvascular density of ovariectomized SHRs. Moreover, when simultaneously administered, oestradiol and captopril had an additive effect on blood pressure and the microvasculature.

Hypertension-independent microvascular rarefaction in the obese Zucker rat model of the metabolic syndrome

OBJECTIVE

To test the hypothesis that reduced skeletal muscle microvessel density (MVD) in obese Zucker rats (OZR) is independent of chronic elevations in mean arterial pressure (MAP).

METHODS

Microvessels in cross sections of gastrocnemius muscle from lean Zucker rats (LZR) and OZR were labeled with Griffonia simplicifolia I lectin, visualized with fluorescence microscopy and vessel number within sections was determined using imaging software. Rats were used at different ages to assess correlations between the temporal development of hypertension and microvascular rarefaction. Additionally, rats were chronically treated with captopril or hydralazine as antihypertensive therapies to examine the development of microvascular rarefaction in the absence of elevated blood pressure.

RESULTS

MVD in muscle of OZR was reduced by approximately 17% versus LZR by 10-11 weeks of age, prior to any elevation in MAP. By 15-17 weeks, OZR exhibited a approximately 23% reduction in MVD and a approximately 25 mmHg increase in MAP. Treatment with hydralazine prevented elevated MAP in OZR, although this was not associated with an improved MVD. Captopril treatment also prevented elevated MAP in OZR, although a partial recovery of MVD toward normal levels was observed. This observation was associated with an improved insulin resistance.

CONCLUSIONS

These results suggest that microvessel rarefaction in skeletal muscle of OZR manifesting the metabolic syndrome does not depend on an elevated mean arterial pressure and that other factors associated with the metabolic syndrome, possibly insulin resistance, may underlie the progressive reduction in MVD in these animals.

Selecting antihypertensive drug therapy: the JNC-V controversy

OBJECTIVE

To present both the supporting and the opposing arguments for the fifth set of recommendations issued by the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC).

METHODS

The published studies are reviewed, and the various opinions are discussed.

RESULTS

The 1993 recommendation from the JNC that diuretics or beta-adrenergic blockers be preferred for therapy in most patients with hypertension has proved controversial. This recommendation derived primarily from recent long-term studies showing convincing reductions in cardiovascular morbidity and mortality when these agents are used to control hypertension. Comparable data have not yet been obtained for newer agents, such as calcium channel blockers and angiotensin-converting enzyme inhibitors. Nonetheless, some critics of the JNC recommendation still favor the newer agents because of their putatively superior side-effect profile, from both a metabolic and a compliance standpoint.

CONCLUSION

The issue of optimal antihypertensive drug therapy will not be definitively resolved until long-term studies directly comparing the various classes of agents are completed in future years.

Effects of sesamin on aortic oxidative stress and endothelial dysfunction in deoxycorticosterone acetate-salt hypertensive rats

In the present study, we evaluated the relationship between the antihypertensive effect of sesamin, a lignan from sesame oil, and its antioxidative activity in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. After a 5-week treatment period, systolic blood pressure was significantly elevated in normal diet-fed DOCA-salt animals compared with cases in sham-operated animals. Sesamin feeding, tempol (a superoxide dismutase mimetic) treatment or antihypertensive drugs combination (triple therapy; reserpine, hydralazine, hydrochlorothiazide) significantly suppressed the development of DOCA-salt-induced hypertension. Compared with sham-operated rats, the normal diet-fed DOCA-salt rats revealed marked increases in aortic superoxide (O(2)(-)) production. These increases in O(2)(-) production were significantly suppressed by sesamin feeding or tempol treatment, but not by triple therapy. Acetylcholine (Ach)-induced endothelium-dependent relaxation was markedly decreased in normal diet-fed DOCA-salt rats, compared with cases in sham-operated rats. Sesamin feeding and triple therapy significantly improved the DOCA-salt-induced impairment of endothelium-dependent relaxation. However, tempol treatment had no effect on the impaired vasodilator responses induced by DOCA-salt treatment. In DOCA-salt rats with or without sesamin feeding, systolic blood pressure significantly correlated with both aortic O(2)(-) production and endothelium-dependent vascular relaxation. These findings suggest that sesamin feeding inhibits the enhancement of aortic O(2)(-) production in DOCA-salt hypertensive rats, and this effect may contribute to the antihypertensive effect of sesamin. Sesamin feeding-induced improvement of endothelial dysfunction seems to result from the above antioxidative and antihypertensive effects.

Effect of high-salt diet or chronic captopril treatment on exercise capacity in normotensive rats

1. We investigated whether chronic suppression of the renin-angiotensin system, which is known to be associated with reductions in microvascular density and vasodilator responsiveness of skeletal muscle, could affect exercise capacity in normotensive rats. 2. Rats were placed on normal rat chow, normal rat chow with captopril (100 mg/kg per day) or a high-salt diet (HS; 4%) for 4 weeks. Following these interventions, rats with indwelling carotid artery catheters were submitted to stepwise increasing exercise on a motor treadmill at a speed of 10, 20 and 30 m/min for 4 min while blood lactate was measured. 3. Blood lactate after exercise at a speed of 20 m/min was significantly higher and the duration during which rats were able to run at a speed of 30 m/min was significantly shorter in captopril-treated rats and rats fed an HS diet compared with control rats. 4. We conclude that chronic treatment with captopril or HS diet could reduce the exercise capacity in inactive normotensive rats, probably through chronic inhibition of the renin-angiotensin system.

N-acetyl-seryl-aspartyl-lysyl-proline stimulates angiogenesis in vitro and in vivo

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), a natural inhibitor of pluripotent hematopoietic stem cell proliferation, has been suggested as capable of promoting an angiogenic response. We studied whether Ac-SDKP stimulates endothelial cell proliferation, migration, and tube formation; enhances angiogenic response in the rat cornea after implantation of a tumor spheroid; and increases capillary density in rat hearts with myocardial infarction (MI). In vitro, an immortal BALB/c mouse aortic endothelial 22106 cell line was used to determine the effects of Ac-SDKP on endothelial cell proliferation and migration and tube formation. In vivo, a 9L-gliosarcoma cell spheroid (250-300 microm in diameter) was implanted in the rat cornea and vehicle or Ac-SDKP (800 microg.kg(-1).day(-1) ip) infused via osmotic minipump. Myocardial capillary density was studied in rats with MI given either vehicle or Ac-SDKP. We found that Ac-SDKP 1) stimulated endothelial cell proliferation and migration and tube formation in a dose-dependent manner, 2) enhanced corneal neovascularization, and 3) increased myocardial capillary density. Endothelial cell proliferation and angiogenesis stimulated by Ac-SDKP could be beneficial in cardiovascular diseases such as hypertension and MI. Furthermore, because Ac-SDKP is mainly cleaved by ACE, it may partially mediate the cardioprotective effect of ACE inhibitors.

A novel angiotensin II type 1 receptor-associated protein induces cellular hypertrophy in rat vascular smooth muscle and renal proximal tubular cells

Angiotensin II stimulates cellular hypertrophy in cultured vascular smooth muscle and renal proximal tubular cells. This effect is believed to be one of earliest morphological changes of heart and renal failure. However, the precise molecular mechanism involved in angiotensin II-induced hypertrophy is poorly understood. In the present study we report the isolation of a novel angiotensin II type 1 receptor-associated protein. It encodes a 531-amino acid protein. Its mRNA is detected in all human tissues examined but highly expressed in the human kidney, pancreas, heart, and human embryonic kidney cells as well as rat vascular smooth muscle and renal proximal tubular cells. Protein synthesis and relative cell size analyzed by flow cytometry studies indicate that overexpression of the novel angiotensin II type 1 receptor-associated protein induces cellular hypertrophy in cultured rat vascular smooth muscle and renal proximal tubular cells. In contrast, the hypertrophic effects was reversed in renal proximal tubular cell lines expressing the novel gene in the antisense orientation and its dominant negative mutant, which lacks the last 101 amino acids in its carboxyl-terminal tail. The hypertrophic effects are at least in part mediated via protein kinase B activation or cyclin-dependent kinase inhibitor, p27(kip1) protein expression level in vascular smooth muscle, and renal proximal tubular cells. Moreover, angiotensin II could not stimulate cellular hypertrophy in renal proximal tubular cells expressing the novel gene in the antisense orientation and its mutant. These findings may provide new molecular mechanisms to understand hypertrophic agents such as angiotensin II-induced cellular hypertrophy.

Transmembrane proteases in cell growth and invasion: new contributors to angiogenesis?

Transmembrane proteases (TPs) are proteins anchored in the plasma membrane with their catalytic site exposed to the external surface of the membrane. TPs are widely expressed, and their dysregulated expression is associated with cancer, infection, inflammation, autoimmune and cardiovascular diseases, all diseases where angiogenesis is part of the pathology. TPs participate in extracellular proteolysis (degradation of extracellular matrix components, regulation of chemokine activity, release of membrane-anchored cytokines, cytokine receptors and adhesion molecules) and influence cell functions (growth, secretion of angiogenic molecules, motility). Recent attention has been focused on the ADAM-17 (a disintegrin and metalloprotease)/TACE/CD156q, the MT1-MMP (membrane-type-1 matrix metallo proteinase)/MMP-14, and the ectopeptidases aminopeptidase N (APN/CD13), dipeptidyl peptidase IV (DPPIV/CD26) and angiotensin-converting enzyme (ACE/CD143), that appear to have a critical role in angiogenesis. This article summarizes current knowledge on these TPs, and reviews recent investigations that document their participation during angiogenic-related events. Through their multiple roles, TPs may thereby provide critical links in angiogenesis.

Does the angiotensin II receptor antagonist losartan improve cognitive function?

Newer classes of antihypertensive agents, such as angiotensin II receptor antagonists, may offer benefits to patients in addition to their ability to lower blood pressure. It is accepted that chronic hypertension contributes to the development of cerebrovascular and cardiovascular disease, and several studies have demonstrated a link between hypertension and reduced cognitive function, especially in patients not receiving antihypertensive medication. In an initial clinical trial, the angiotensin II receptor antagonist losartan was shown to improve cognitive function in patients with hypertension, including in those who were elderly (up to 73 years of age). This effect cannot be explained by a reduction in blood pressure alone and is likely to involve interactions with the diverse biological actions of the renin-angiotensin system. Improving or maintaining cognitive function in patients with hypertension may translate into economic benefits beyond those expected due to blood pressure control, and would result in considerable quality-of-life benefits for the aging population.

Ramipril improves hemodynamic recovery but not microvascular response to ischemia in spontaneously hypertensive rats

BACKGROUND

Angiotensin converting enzyme (ACE) inhibition exerts positive effects on the microvasculature of normotensive animals, although this concept is not universally accepted. Recently, ACE inhibitors have been suggested to be useful for rescue in peripheral ischemia.

METHODS

We investigated whether chronic treatment with the ACE inhibitor ramipril may have a positive impact on the defective healing response to ischemia that is typical of spontaneously hypertensive rats (SHR). Unilateral limb ischemia was induced in 20-week-old SHR by surgically removing the left femoral artery. Rats were allowed to regain consciousness and then were randomly allocated to treatment with ramipril (1 mg/kg body weight in drinking water) or vehicle for 28 days.

RESULTS

The SHR failed to develop reparative angiogenesis in response to ischemia, thus having inadequate perfusion recovery. Ramipril reduced both tail-cuff systolic blood pressure (180 +/- 7 v 207 +/- 2 mm Hg in the vehicle group at 28 days, P < .05) and intra-arterial mean blood pressure (115 +/- 6 v 135 +/- 5 mm Hg in the vehicle group, P < .05). These effects were associated with increased responsiveness to endothelium-dependent vasodilatation by acetylcholine. Treatment with ramipril did not influence muscular capillary and arteriole density but accelerated the rate of perfusion recovery, leading to complete healing within 28 days after surgery.

CONCLUSIONS

These results indicate that ACE inhibition by ramipril may be useful for the treatment of peripheral vascular complications in hypertension.

Endothelial nitric oxide synthase lies downstream from angiotensin II-induced angiogenesis in ischemic hindlimb

We assessed the role of angiotensin (Ang) II in ischemia-induced angiogenesis and analyzed the molecular pathways involved in such an effect. Ischemia was produced by unilateral artery femoral occlusion in control, in valsartan-treated (Ang II receptor type I antagonist, 20 mg/kg per day), in Ang II-treated (5 ng/kg per min), and in Ang II and valsartan-treated rats. After 28 days, angiogenesis was assessed by microangiography and capillary density measurement in hindlimbs. The ischemic/nonischemic leg ratio for angiographic score and capillary number increased by 2.6- and 2-fold, respectively, in Ang II-treated rats compared with controls (P<0.01). This was associated with an increase in vascular endothelial growth factor (VEGF; 1.6-fold) and endothelial NO synthase (eNOS; 1.8-fold) protein content within the ischemic leg, assessed by Western blot. Angiotensin type 1 receptor blockade and administration of VEGF neutralizing antibody (2.5 microg IP, twice a week) in Ang II-treated rats completely prevented such Ang II angiogenic effects. The key role of eNOS was then emphasized by using mice deficient in gene encoding for eNOS. In wild-type mice, Ang II (0.3 mg/kg per min) treatment increased by 1.7- and 1.6-fold the ischemic/nonischemic leg for angiographic score and blood perfusion (assessed by laser Doppler perfusion imaging) ratios, respectively (P<0.01). Conversely, no significant changes were observed in Ang II-treated mice deficient in gene encoding for eNOS. Subhypertensive dose of Ang II enhanced angiogenesis associated with tissue ischemia through angiotensin type 1 receptor activation that involved the VEGF/eNOS-dependent pathway.

Cigarette smoking and vascular pathology in renal biopsies

BACKGROUND

In recent years cigarette smoking has been identified as a progression factor in chronic nephropathies such as glomerulonephritis or diabetic nephropathy. The exact pathomechanism of nicotine-induced renal damage is, however, unknown. Autopsy studies and functional investigations suggest that the renal vasculature is primarily affected by smoking.

METHODS

Renal vascular pathology, that is, glomerulosclerosis, hyalinosis of arterioles and myointimal hyperplasia of small arteries, was determined in 135 biopsies of patients over thirty years of age. A questionnaire about smoking habits was returned by 107 of the patients. For glomerular sclerosis the percentage of sclerotic glomeruli was determined, whereas arteriolar hyalinosis and myointimal hyperplasia of small arteries were described as present or absent without further quantification. A univariate analysis was performed for existence of vascular changes and ever-smoking status. In addition, a multivariate analysis for glomerular sclerosis and logistic regression analysis for arteriolar hyalinosis and myointimal hyperplasia and the variables ever-smoking, age, body mass index, creatinine clearance, blood pressure and lipids were performed.

RESULTS

Creatinine clearance was comparable for nonsmokers, ex-smokers and smokers. Frequency of myointimal hyperplasia of small arteries was twice as high in ever-smokers as compared to nonsmokers (50% vs. 25.5%, P < 0.01). Arteriolar hyalinosis was detected in 23.5% of nonsmokers and in 35.7% of smokers, showing a trend toward hyalinosis in ever-smokers (P=0.20). Glomerular sclerosis was found in 62.7% of nonsmokers and in 69.6% of ever-smokers. Logistic regression analysis confirmed an association between ever-smoking and myointimal hyperplasia (P < 0.01). This association also was present in males and patients over fifty years of age, but not in younger patients and females.

CONCLUSION

In patients with renal, especially glomerular disease, cigarette smoking exhibits its deleterious effect on the kidneys primarily through damage of small interlobular arteries.

Angiotensin AT(1) receptor signalling modulates reparative angiogenesis induced by limb ischaemia

1. The concept that angiotensin II exerts pro-angiogenic activity is not universally accepted. We evaluated whether inhibition of the renin-angiotensin system (RAS) would influence reparative angiogenesis in a murine model of limb ischaemia. 2. Perfusion recovery following surgical removal of the left femoral artery was analysed by laser Doppler flowmetry in mice given the ACE inhibitor ramipril (1 mg kg(-1) per day), the AT(1) antagonist losartan (15 mg kg(-1) per day), or vehicle. Muscular capillarity was examined at necroscopy. Ramipril-induced effects were also studied under combined blockade of kinin B(1) and B(2) receptors. Furthermore, the effects of ischaemia on AT(1) gene expression and ACE activity were determined. 3. In untreated mice, muscular AT(1a) gene expression was transiently decreased early after induction of limb ischaemia, whereas AT(1b) mRNA was up-regulated. ACE activity was reduced in ischaemic muscles at 1 and 3 days. Gene expression of AT(1) isoforms as well as ACE activity returned to basal values by day 14. Spontaneous neovascularization allowed for complete perfusion recovery of the ischaemic limb after 21 days. 4. Reparative angiogenesis was negatively influenced by either ramipril (P<0.02) or losartan (P<0.01), leading to delayed and impaired post-ischaemic recovery (50 - 70% less compared with controls). Ramipril-induced effects remained unaltered under kinin receptor blockade. 5. The present study indicates that (a) expression of angiotensin II AT(1) receptors and ACE activity are modulated by ischaemia, (b) ACE-inhibition or AT(1) antagonism impairs reparative angiogenesis, and (c) intact AT(1) receptor signalling is essential for post-ischaemic recovery. These results provide new insights into the role of the RAS in vascular biology and suggest cautionary use of ACE inhibitors and AT(1) antagonists in patients at risk for developing peripheral ischaemia.

AT1 receptor is present in glioma cells; its blockage reduces the growth of rat glioma

Malignancy of neoplasms is partly dependent on angiogenesis. Angiotensin II mediates angiogenesis and transcription of growth-related factors through stimulation of the AT1 receptor (AT1R). Losartan, a drug used mostly for treatment of hypertension, binds strongly to this receptor. We found the presence of AT1 receptor on C6 glioma cells and studied the effect of Losartan on the growth and angiogenesis of C6 rat glioma; Losartan in dose of 80 mg/kg induced 79% reduction of tumoural volume with a significant decrease of vascular density, mitotic index and cell proliferation. Our results demonstrate the conspicuous presence of AT1R in malignant glial cells and a favourable therapeutic response in experimental glioma by selective blockage of the AT1 receptor.

Antihypertensive effects of chicken extract against deoxycorticosterone acetate-salt-induced hypertension in rats

We investigated the antihypertensive effect of Brand's Essence of Chicken (BEC), a popular chicken extract used as a traditional remedy, using deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Animals were unilaterally nephrectomized, and then separated into a sham-operated group (sham group) and a DOCA-salt-treated group. The latter was further separated into a normal diet group and a BEC (freeze-dried powder, 0.1 w/w%)-containing diet group. Systolic blood pressure of the normal diet group progressively increased in comparison with that of the sham group. The DOCA-salt-induced hypertension was markedly suppressed by feeding a BEC-containing diet. Systolic blood pressure after 5 weeks was 128+/-2 mmHg in sham group, 181+/-4 mmHg in the DOCA-salt-treated normal diet group and 139+/-5 mmHg in the DOCA-salt-treated BEC diet group, respectively. The treatment with DOCA and salt for 5 weeks significantly increased the weights of heart and left ventricle, but these increases were significantly suppressed in the BEC group. When the degree of vascular hypertrophy of the aorta was histochemically evaluated, DOCA-salt-induced increases in wall thickness and wall area of the vessels were significantly decreased by the BEC-feeding. Histopathological renal damage of fibrinoid-like necrosis in glomeruli, thickening of small arteries and tubular dilatation were observed in the DOCA-salt-treated normal diet group, but this damage was efficiently reduced by the BEC-feeding. In addition, BEC-feeding decreased urinary excretion of protein, which was elevated by the treatment with DOCA and salt. Thus, BEC seems to be useful as a prophylactic treatment in the development of hypertension and related tissue injuries.

Ovarian hormones modulate endothelin-1 vascular reactivity and mRNA expression in DOCA-salt hypertensive rats

We previously demonstrated a differential activation of the endothelin-1 (ET-1) pathway in male and female deoxycorticosterone (DOCA)-salt hypertensive rats, with the male rats exhibiting marked alterations in vascular and pressor responses to ET-1 and Suc-[Glu,(9)Ala(11,15)]-ET-1(8-21) (IRL-1620), an ET(B) agonist. Mechanisms underlying these gender differences are unclear, and we hypothesized that the ovarian hormones attenuate vascular ET(B) responses in female DOCA-salt rats. Female Wistar rats were randomized in 3 groups: sham-operated, ovariectomized (OVX), and OVX plus hormone replacement with estradiol (E) or estradiol/progesterone (EP). Two weeks later, rats were uninephrectomized and further randomized in DOCA-salt (subcutaneous injections of desoxycorticosterone and drinking water containing NaCl/KCl) and control normotensive (subcutaneous injections of vehicle and tap water). Blood pressure was evaluated both by direct and standard tail-cuff methods. Responses to IRL-1620 were evaluated in vivo/in situ in the mesenteric microcirculation. mRNA expression of ET-1 and ET(A/B) receptors was evaluated in mesenteric arteries by reverse transcription-polymerase chain reaction and expressed relative to GAPDH. OVX-DOCA rats developed a more severe form of hypertension than did DOCA rats. Treatment with E or EP restored blood pressure to levels observed in DOCA rats. In the mesentery, IRL-1620 induced vasodilatation in control rats, a mild vasoconstriction in DOCA rats, and marked vasoconstriction in OVX-DOCA rats. Both E and EP decreased IRL-1620-induced vasoconstriction in the DOCA group. In the normotensive group, OVX did not change blood pressure or IRL-1620-induced vasodilation. Removal of the ovaries increased ET-1 mRNA in arteries from DOCA and control rats, although treatment with E or EP reversed these changes. Vascular ET(B) receptor mRNA levels were greatly enhanced in OVX-DOCA but not OVX-control rats. Hormone replacement with E or EP restored ET(B) receptor expression in the DOCA group. A greater blood pressure-lowering effect of bosentan (ET(A)/ET(B) blocker) was observed in OVX-DOCA rats. The observation that OVX worsens hypertension as well as the altered ET(B) receptor-mediated responses and the effects of bosentan in female DOCA rats supports our suggestion that the ovarian hormones modulate ET-1/ET(B) receptor vascular responses/expression in DOCA-salt hypertension.

Angiotensin II AT1 receptors preserve vasodilator reactivity in skeletal muscle resistance arteries

Resistance arteries (100-150 microm) were isolated from the gracilis muscle of normotensive Sprague-Dawley rats placed on a high-salt (HS) diet (4.0% NaCl) for 3-7 days. Exposure to the HS diet eliminated vascular relaxation in response to hypoxia (PO2 reduction to 35-40 Torr) and iloprost, a stable analog of prostacyclin. Vasodilator responses were restored in arteries isolated from chronically instrumented HS rats receiving a continuous intravenous infusion of either angiotensin II (ANG II; 5-6 ng x kg(-1) x min(-1)) or ANG II plus the AT2 receptor blocker PD-123319 (5 microg x kg(-1) x min(-1)) for 3 days before the isolated vessel studies. In contrast, coinfusion of the AT1 receptor blocker losartan (20 microg x kg(-1) x min(-1)) or coinfusion of both receptor blockers with ANG II eliminated the protective effect of ANG II to restore dilator responses to hypoxia and iloprost. Neither a HS diet nor ANG II infusion affected the dilation of gracilis arteries in response to direct activation of adenylyl cyclase by forskolin, suggesting that the effect of both the HS diet and the ANG II on the vasculature is mediated upstream from second messenger systems. These findings indicate that the protective effect of ANG II to maintain vasodilator reactivity in resistance arteries of rats on a HS diet is mediated via the AT1 receptor subtype.

ANG II is required for optimal overload-induced skeletal muscle hypertrophy

ANG II mediates the hypertrophic response of overloaded cardiac muscle, likely via the ANG II type 1 (AT(1)) receptor. To examine the potential role of ANG II in overload-induced skeletal muscle hypertrophy, plantaris and/or soleus muscle overload was produced in female Sprague-Dawley rats (225-250 g) by the bilateral surgical ablation of either the synergistic gastrocnemius muscle (experiment 1) or both the gastrocnemius and plantaris muscles (experiment 2). In experiment 1 (n = 10/group), inhibiting endogenous ANG II production by oral administration of an angiotensin-converting enzyme (ACE) inhibitor during a 28-day overloading protocol attenuated plantaris and soleus muscle hypertrophy by 57 and 96%, respectively (as measured by total muscle protein content). ACE inhibition had no effect on nonoverloaded (sham-operated) muscles. With the use of new animals (experiment 2; n = 8/group), locally perfusing overloaded soleus muscles with exogenous ANG II (via osmotic pump) rescued the lost hypertrophic response in ACE-inhibited animals by 71%. Furthermore, orally administering an AT(1) receptor antagonist instead of an ACE inhibitor produced a 48% attenuation of overload-induced hypertrophy that could not be rescued by ANG II perfusion. Thus ANG II may be necessary for optimal overload-induced skeletal muscle hypertrophy, acting at least in part via an AT(1) receptor-dependent pathway.

Enalapril prevents aortic hyperreactivity and remodelling in one-kidney, one-clip hypertensive rats without reducing arterial pressure

1. The present study was designed to evaluate the blood pressure-independent effects of angiotensin-converting enzyme (ACE) inhibition on cardiovascular structure and function in one-kidney, one-clip (1K1C) hypertensive rats. 2. The study was conducted in four groups of rats: (i) uninephrectomized normotensive rats (1K); (ii) 1K1C hypertensive rats; (iii) 1K rats treated with enalapril; and (iv) 1K1C rats treated with enalapril. Enalapril treatment (20 mg/kg per day, p.o.) was started after surgery to induce hypertension or nephrectomy and continued for 5 weeks. 3. The increase in blood pressure of 1K1C rats was associated with activation of cardiac and aortic, but not plasma, ACE activity and with hypertrophy of both heart and aorta. No difference in cardiac output and in vitro systolic function was observed among the groups. Hypertrophied aorta isolated from 1K1C rats displayed increased sensitivity to phenylephrine (PE) and unaltered responses to both acetylcholine (ACh) and sodium nitroprusside compared with the 1K group. 4. Enalapril treatment effectively inhibited plasma and tissue ACE activity in 1K1C and 1K rats. Enalapril did not prevent the development of hypertension and cardiac hypertrophy nor did it change haemodynamic parameters in 1K1C rats. However, enalapril prevented the increase in aortic media thickness and cross-sectional area and restored the hypersensitivity to PE in aortic rings of 1K1C rats. The endothelium-dependent response to ACh was enhanced by enalapril in the aorta of 1K but not 1K1C rats. 5. These results suggest a role for activated local angiotensin II generation in aortic but not cardiac hypertrophy secondary to 1K1C hypertension.

Reinforcement of arteriolar myogenic activity by endogenous ANG II: susceptibility to dietary salt

The purpose of this study was to determine whether endogenous ANG II augments arteriolar myogenic behavior in striated muscle. Because circulating ANG II is decreased during high salt intake, we also investigated whether dietary salt could alter any influence of ANG II on myogenic behavior. Normotensive rats fed low-salt (0.45%, LS) or high-salt (7%, HS) diets were enclosed in a ventilated box with the spinotrapezius muscle exteriorized for intravital microscopy. Dietary salt did not affect resting arteriolar diameters. Microvascular pressure elevation by box pressurization caused greater arteriolar constriction in LS rats (up to 12 microm) than in HS rats (up to 4 microm). The ANG II-receptor antagonists saralasin and losartan attenuated myogenic responsiveness in LS rats but not HS rats. The bradykinin-receptor antagonist HOE-140 had no effect on myogenic responsiveness in LS rats but augmented myogenic responsiveness in HS rats. HOE-140 with the angiotensin-converting enzyme inhibitor captopril attenuated myogenic responsiveness to a greater extent in LS rats than in HS rats. We conclude that endogenous ANG II normally reinforces arteriolar myogenic behavior in striated muscle and that attenuated myogenic behavior associated with high salt intake is due to decreased circulating ANG II and increased local kinin levels.

Effect of captopril on neurally induced contraction and relaxation of mesenteric arteries of renal hypertensive rats

The effect of captopril treatment on neurally induced vasoconstrictor and vasodilator responses was examined in the isolated mesenteric arterial bed from normotensive and one-kidney, one clip hypertensive (1K1C) rats. In isolated mesenteric beds, electrical field stimulation (EFS) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was greater in preparations from hypertensive rats compared with those from normotensive rats. Captopril treatment was associated with a decrease in vasoconstrictor responses in the hypertensive group compared with its non-treated control. Responses to norepinephrine (320 ng) were greater in hypertensive than normotensive groups; captopril reduced this response only in the hypertensive group. In preconstricted mesenteric arteries perfused with solutions containing guanethidine (5 µM) and atropine (1 µM), EFS elicited a frequency-dependent decrease in perfusion pressure that was abolished by tetrodotoxin (1 µM). Vasodilator responses to EFS were not affected by captopril treatment, although they were smaller in the hypertensive group. Acetylcholine (10 ng) induced similar decreases in perfusion pressure of normotensive and 1K1C groups; captopril did not influence these responses. These results indicate that captopril treatment does not affect the reduced neurogenic vasodilation but normalizes the augmented sympathetic-mediated vasoconstrictor responses of mesenteric resistance vessels of chronic 1K1C hypertensive rats.Key words: neurogenic vasodilation, calcitonin gene-related peptide, angiotensin, renal hypertension, angiotensin converting enzyme.

Effect of captopril on skeletal muscle angiogenic growth factor responses to exercise

Acute exercise increases vascular endothelial growth factor (VEGF), transforming growth factor-beta(1) (TGF-beta(1)), and basic fibroblast growth factor (bFGF) mRNA levels in skeletal muscle, with the greatest increase in VEGF mRNA. VEGF functions via binding to the VEGF receptors Flk-1 and Flt-1. Captopril, an angiotensin-converting enzyme inhibitor, has been suggested to reduce the microvasculature in resting and exercising skeletal muscle. However, the molecular mechanisms responsible for this reduction have not been investigated. We hypothesized that this might occur via reduced VEGF, TGF-beta(1), bFGF, Flk-1, and Flt-1 gene expression at rest and after exercise. To investigate this, 10-wk-old female Wistar rats were placed into four groups (n = 6 each): 1) saline + rest; 2) saline + exercise; 3) 100 mg/kg ip captopril + rest; and 4) 100 mg/kg ip captopril + exercise. Exercise consisted of 1 h of running at 20 m/min on a 10 degrees incline. VEGF, TGF-beta(1), bFGF, Flk-1, and Flt-1 mRNA were analyzed from the left gastrocnemius by quantitative Northern blot. Exercise increased VEGF mRNA 4.8-fold, TGF-beta(1) mRNA 1.6-fold, and Flt-1 mRNA 1.7-fold but did not alter bFGF or Flk-1 mRNA measured 1 h after exercise. Captopril did not affect the rest or exercise levels of VEGF, TGF-beta(1), bFGF, and Flt-1 mRNA. Captopril did reduce Flk-1 mRNA 30-40%, independently of exercise. This is partially consistent with the suggestion that captopril may inhibit capillary growth.

In spontaneously hypertensive rats alterations in aortic wall properties precede development of hypertension

In hypertension arterial wall properties do not necessarily depend on increased blood pressure alone. The present study investigates the relationship between the development of hypertension and thoracic aortic wall properties in 1.5-, 3-, and 6-mo-old spontaneously hypertensive rats (SHR); Wistar-Kyoto rats (WKY) served as controls. During ketamine-xylazine anesthesia, compliance and distensibility were assessed by means of a noninvasive ultrasound technique combined with invasive blood pressure measurements. Morphometric measurements provided in vivo media cross-sectional area and thickness, allowing the calculation of the incremental elastic modulus. Extracellular matrix protein contents were determined as well. Blood pressure was not significantly different in 1.5-mo-old SHR and WKY, but compliance and distensibility were significantly lower in SHR. Incremental elastic modulus was not significantly different between SHR and WKY at this age. Media thickness and media cross-sectional area were significantly larger in SHR than in WKY, but there was no consistent difference in collagen density and content between the strains. Blood pressure was significantly higher in 3- and 6-mo-old SHR than in WKY, and compliance was significantly lower in SHR. The findings in this study show that in SHR, in which hypertension develops over weeks, alterations in functional aortic wall properties precede the development of hypertension. The decrease in compliance and distensibility at a young age most likely results from media hypertrophy rather than a change in intrinsic elastic properties.

Reduced renal mass hypertension, but not high salt diet, alters skeletal muscle arteriolar distensibility and myogenic responses

The effects of high salt diet and reduced renal mass hypertension (RRM-HT) on skeletal muscle arteriolar distensibility and myogenic responses were investigated in male Sprague-Dawley rats. Rats were enclosed in an air-tight box with the in situ cremaster muscle exteriorized and viewed via television microscopy. Normotensive rats were fed low salt (0.4% NaCl) or high salt (4.0% NaCl) diet and RRM-HT rats were fed high salt diet for 4-6 weeks. With the cremaster muscle superfused with either physiological salt solution (for myogenic responses) or Ca(2+)-free physiological salt solution (for arteriolar distensibility), box pressure (and therefore, intravascular pressure) was increased in 5 mm Hg increments to a maximum of +30 mm Hg. The myogenic responses of arterioles were not altered by high salt diet, but were enhanced with RRM-HT. Arteriolar distensibility was not affected by high salt diet, but was reduced in RRM-HT rats compared to either normotensive rat group. These data suggest that high salt diet does not significantly alter either myogenic responses or the distensibility of rat cremasteric arterioles. However, RRM-HT enhances myogenic responses of these vessels while reducing arteriolar distensibility. The impact of these effects must be taken into account when interpreting data describing alterations in skeletal muscle microvessel reactivity for animals on high salt diet or with RRM hypertension.

AT(1) receptor inhibition does not reduce arterial wall hypertrophy or PDGF-A expression in renal hypertension

To separate the role of ANG II from pressure in hypertrophy of the vascular wall in one-kidney, one-clip (1K1C) hypertension, experimental and sham-operated rats were given the AT(1)-receptor antagonist losartan (20 mg x kg(-1) x day(-1)) or tap water for 14 days. Mean arterial pressure was elevated in both experimental groups compared with controls. Rats were anesthetized with pentobarbital sodium, and the thoracic aorta and carotid, small mesenteric, and external spermatic arteries were harvested and embedded in paraffin. Tissue sections were used for morphological analysis, immunohistochemistry for 5-bromo-2'-deoxyuridine (BrdU) and platelet-derived growth factor (PDGF)-AA, stereological measurements, and in situ hybridization with a (35)S-labeled riboprobe for PDGF-A mRNA. Elevated cross-sectional areas of thoracic, carotid, and small mesenteric artery in 1K1C rats were not reduced by losartan. The internal diameter of the external spermatic artery and microvascular density of the cremaster muscle were reduced in 1K1C rats. The number of BrdU-positive nuclei per cross section did not differ between 1K1C and control arteries. PDGF-A mRNA was elevated in the arterial walls of 1K1C rats compared with controls and was hardly changed by losartan. PDGF-A protein stained strongly in the media of 1K1C arteries and was not inhibited by losartan; it appeared in the adventitia of all aortas and carotid arteries. These observations demonstrate that effects of ANG II mediated through the AT(1) receptor are not necessary for hypertrophy of the vascular wall during 1K1C hypertension or expression of PDGF-A.

Limitation of arteriolar myogenic activity by local nitric oxide: segment-specific effect of dietary salt

The purpose of this study was to determine if local nitric oxide (NO) activity attenuates the arteriolar myogenic response in rat spinotrapezius muscle. We also investigated the possibility that hypertension, dietary salt, or their combination can alter any influence of local NO on the myogenic response. Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) fed low-salt (0.45%, LS) or high-salt (7%, HS) diets were enclosed in a ventilated airtight box with the spinotrapezius muscle exteriorized for intravital microscopy. Mean arterial pressure was unaffected by dietary salt in WKY but was significantly higher and augmented by dietary salt in SHR. In all experiments, elevation of microvascular pressure by box pressurization caused a 0-30% decrease in the diameter of large (arcade bridge) arterioles and a 21-27% decrease in the diameter of intermediate (arcade) arterioles. Inhibition of NO synthase with N(G)-monomethyl-L-arginine (L-NMMA) significantly enhanced myogenic responsiveness of arcade bridge arterioles in WKY-LS and SHR-LS but not in WKY-HS and SHR-HS. L-NMMA significantly enhanced the myogenic responsiveness of arcade arterioles in all four groups. Excess L-arginine reversed this effect of L-NMMA in all cases, and arteriolar responsiveness to the NO donor sodium nitroprusside was not different among the four groups. High-salt intake had no effect on the passive distension of arterioles in either strain during box pressurization. We conclude that 1) local NO normally attenuates arteriolar myogenic responsiveness in WKY and SHR, 2) dietary salt impairs local NO activity in arcade bridge arterioles of both strains, and 3) passive arteriolar distensibility is not altered by a high-salt diet in either strain.

Modulation and function of extrarenal angiotensin receptors

Historically, physiological modulation of the activity of the renin-angiotensin system (RAS) was thought to be mediated only by changes in renin secretion. Hence, altered dietary sodium (Na) intake, changes in renal perfusion pressure, and/or renal adrenoreceptor activity would lead to changes in renin release and plasma angiotensin II (Ang II) concentration, which in turn contribute to regulation of blood pressure and sodium balance. Later, it became apparent that angiotensinogen availability and Ang-converting enzyme activity are also rate-limiting factors that influence the activity of RAS. Finally, over the past few years, evidence has accumulated that indicates the number of Ang II receptors and their subtypes are of great importance in regulating the activity and function of RAS. Cloning of the Ang II receptor genes, development of specific receptor-antagonist ligands, and establishment of genetically mutated animal models have led to greater understanding of the role of Ang II receptors in the regulation of RAS function and activity. This review focuses on the functions and regulation of Ang II receptors in vascular tissues and in the adrenal gland. The authors suggest that identification of control elements for Ang II receptor expression, which are tissue-specific, may provide a basis for future therapeutic manipulation of Ang II receptors in cardiovascular disease states.

Angiotensinogen T174M and M235T gene polymorphisms are associated with the extent of coronary atherosclerosis

BACKGROUND

The relations of the angiotensinogen (AGT) T174M and M235T gene polymorphisms to the risk of coronary heart disease (CHD) have been investigated in only a few studies with conflicting results.

RESULTS

Therefore, we analysed the relationship of the AGT gene polymorphisms to the presence and extent of CHD in 2250 male Caucasians whose coronary anatomy was defined by means of coronary angiography. The relative frequencies of the T and M alleles of the T174M and of the M235T gene variation did not significantly differ between patients without or with single-, double- or triple-vessel disease and between subjects without or with myocardial infarction (MI). In contrast the mean CHD score--defined by Gensini--was higher within MM homozygotes of the T174M gene variation than within TT genotypes; TM subjects had intermediate values. In M235T genotypes, mean CHD scores were similar in the total sample and in older individuals (> or = 62 years), whereas in younger individuals (< 62 years) a higher CHD score was found within AGT 235 T allele carriers than within MM homozygotes. In younger individuals with high apoAI plasma levels, the mean CHD score was clearly higher within TT homozygotes of the M235T gene variation than within MM genotypes; MT subjects had intermediate values. An interaction between both angiotensinogen gene polymorphisms on the extent of CHD or on the risk of non-fatal MI were not observed when the M allele of AGT T174M was combined either with the T allele or the TT genotype of M235T.

CONCLUSIONS

The present study strengthens the hypothesis of an association of both angiotensinogen gene polymorphisms with the extent of coronary heart disease.

Enalapril improves arterial elastic properties in rats with myocardial infarction

Systemic arterial elastic properties, important determinants of left ventricular function and coronary blood flow, are compromised in myocardial infarction (MI). The cardiac effect of angiotensin-converting enzyme inhibitors (ACEIs) has been extensively studied, whereas their arterial effect has been poorly reported in MI. The aim of this work was to study the effect of prolonged ACEI enalapril treatment on systemic arterial structure and elastic properties in rats with MI. One week after the induction of an MI, 40 male Wistar rats received either no treatment (n = 20) or ACEI enalapril (2 mg/kg; n = 20) for 17 weeks. At the end of the treatment period, blood pressure, cardiac output, total peripheral resistance, systemic arterial compliance, characteristic impedance, and left ventricular power were measured in anesthetized rats. Then the rats were killed for infarct-size determination and aortic histomorphometric study. Infarct size, heart, and left and right ventricular weights were similar in the ACEI-treated and untreated infarcted rats. Prolonged ACEI enalapril treatment reduced blood pressure by 17% (p < 0.001), total peripheral resistance by 22% (p < 0.01), and characteristic impedance by 26% (p < 0.03), and increased systemic arterial compliance by 35% (p < 0.01), in comparison with untreated infarcted rats. Enalapril reduced aortic media wall thickness by 9% (p < 0.02) and increased elastin content by 22% (p < 0.03) and elastin-to-collagen content ratio by 42% (p < 0.01). Enalapril did not affect cardiac output and left ventricular power. Smooth muscle cell nuclei number and size and collagen content of aortic wall were similar in the ACEI-treated and untreated infarcted rats. These results indicate that long-term treatment with ACEI enalapril improves arterial elastic properties through structural modifications of arterial wall in rats with MI. This vascular effect may contribute to improve the left ventricular function and the coronary perfusion of infarcted myocardium, and added to the cardiac effect, may explain the prevention of left ventricular remodeling observed with ACEI in this model.

Tissue inhibition of angiotensin-converting enzyme activity stimulates angiogenesis in vivo

BACKGROUND

Endothelial cells (ECs) represent the critical cellular element responsible for postnatal angiogenesis. Because ACE inhibitors may favorably affect endothelial function, we investigated the hypothesis that administration of the ACE inhibitor quinaprilat could enhance angiogenesis in vivo.

METHODS AND RESULTS

Ten days after resection of 1 femoral artery, New Zealand White (NZW) rabbits were randomly assigned to receive recombinant human vascular endothelial growth factor (rhVEGF) administered as a single intra-arterial injection (n=6), quinaprilat (n=8) or captopril (n=7) administered as a daily subcutaneous injection, or no treatment (controls, n=6). Angiogenesis was monitored in vivo by measurement of blood pressure, vasoreactivity, and resistance in ischemic versus normal limbs at day 10 (D10) and D40; angiographic studies to identify sites of neovascularization were performed at D10 and D40, and morphometric analysis of capillary density in the ischemic limb was performed at necropsy (D40). Both functional and morphological outcomes documented augmented angiogenesis in quinaprilat-treated rabbits similar to that observed for rhVEGF and superior to that observed with either captopril or no drug (controls). Residual ACE activity was equivalent for the captopril and quinaprilat groups in plasma (42.54+/-0.03% versus 41.53+/-0.02%, P=NS) but not in tissue, where quinaprilat lowered ACE activity significantly (P<0.01) compared with captopril (13% versus 61%).

CONCLUSIONS

ACE inhibition with quinaprilat promotes angiogenesis in a rabbit model of hindlimb ischemia. Thus, nonsulfhydryl ACE inhibitors with high tissue affinity may be potentially useful for therapeutic angiogenesis in ischemic tissues. Moreover, previous evidence that ACE inhibition benefits patients with myocardial ischemia may be due in part to augmented collateral development.

PDGF-A expression correlates with blood pressure and remodeling in 1K1C hypertensive rat arteries

We previously demonstrated remodeling of large and small arteries in angiotensin II-treated rats, paralleled by an increased expression of platelet-derived growth factor (PDGF)-A chain mRNA in large arteries. Both remodeling and PDGF-A expression were associated with elevation of blood pressure rather than a direct effect of angiotensin II. To further delineate the role of PDGF-A and elevated blood pressure, we assessed the level of PDGF-A and -B mRNA and protein in the wall of large as well as small arteries in the one-kidney, one-clip (1K1C) hypertensive rat, a non-renin-dependent model of hypertension. Fourteen days after renal artery stenosis, the thoracic aorta and both femoral arteries were collected from 1K1C rats (n = 8) and uninephrectomized controls (n = 8) and immediately processed for morphological measurement, immunohistochemistry, RT-PCR, and Western blotting. Systolic blood pressure was significantly elevated in hypertensive rats (202 +/- 26 mmHg) compared with control rats (122 +/- 7.9 mmHg) and was accompanied by arterial hypertrophy in both aorta and femoral arteries. The mRNA for PDGF-A chain was increased threefold in the thoracic aorta (P < 0.05) of 1K1C rats, whereas the message for PDGF-B was not significantly changed in hypertensive versus control animals. A higher staining of the intima-media was observed by using an anti-PDGF-A chain polyclonal antibody on paraffin-embedded sections. Western blot results indicated an approximately 2-fold increase in PDGF-A protein in aortic and femoral wall of the 1K1C rats. The results showed that both the mRNA and protein for PDGF-A chain are increased and well correlated with the blood pressure and wall area, suggesting a direct effect of elevated pressure on PDGF synthesis, which, in turn, may affect the onset and progression of vascular hypertrophy.