Renin-angiotensin-aldosterone System Components Research Articles

Aldosterone Acting Through the Central Nervous System Sensitizes Angiotensin II-Induced Hypertension

Previous studies have shown that preconditioning rats with a nonpressor dose of angiotensin II (Ang II) sensitizes the pressor response produced by later treatment with a higher dose of Ang II and that Ang II and aldosterone (Aldo) can modulate each other’s pressor effects through actions involving the central nervous system. The current studies tested whether Aldo can cross-sensitize the pressor actions of Ang II to enhance hypertension by employing an induction–delay–expression experimental design. Male rats were implanted for telemetered blood pressure recording. During induction, subpressor doses of either subcutaneous or intracerebroventricular Aldo were delivered for 1 week. Rats were then rested for 1 week (delay) to assure that any exogenous Aldo was metabolized. After this, Ang II was given subcutaneously for 2 weeks (expression). During induction and delay, Aldo had no sustained effect on blood pressure. However, during expression, Ang II-induced hypertension was greater in the groups receiving subcutaneous or intracerebroventricular Aldo during induction in comparison with those groups receiving vehicle. Central administration of mineralocorticoid receptor antagonist blocked sensitization. Brain tissue collected at the end of delay and expression showed increased mRNA expression of several renin–angiotensin–aldosterone system components in cardiovascular-related forebrain regions of cross-sensitized rats. Cultured subfornical organ neurons preincubated with Aldo displayed greater increases in [Ca 2+ ] i after Ang II treatment, and there was a greater Fra-like immunoreactivity present at the end of expression in cardiovascular-related forebrain structures. Taken together, these results indicate that Aldo pretreatment cross-sensitizes the development of Ang II-induced hypertension probably by mechanisms that involve the central nervous system.

Effects of ACE-Inhibitors and Angiotensin Receptor Blockers on Inflammation

The role of inflammation in cardiovascular disease and in hypertensive disease above all, is complex. Several studies confirm that activation of renin-angiotensin-aldosterone system (RAAS), through increase in the production of angiotensin II (Ang II), is closely related to local vascular inflammation. Over the BP lowering effects of anti-hypertensive treatments, several ancillary effects for every class may be found, distinguishing the various drugs from one another. Given the pro-inflammatory effects of Ang II and aldosterone, agents that interfere with the components of RAAS, such as ACE inhibitors, Angiotensin Receptor Blockers (ARBs), and mineralocorticoid receptor antagonists (spironolactone or the more selective eplerenone), represent logical therapeutic tools to reduce vascular inflammation and cardiovascular risk, as suggested in large clinical trials in patients with hypertension and diabetes. Regarding ACE inhibitors, actually there is no convincing evidence indicating that ACEi's reduce plasma levels of major inflammatory markers in hypertension models. Lack of evidence concerns especially these inflammation markers, such as fibrinogen of CRP, which are less closely related to atherosclerotic disease and vascular damage and conversely are affected by several more aspecific factors. Results obtained by trials accomplished using ARBs seem to be more univocal to confirm, although to great extent, these is an anti-inflammatory effect of drugs blocking AT1 receptor. In order to strictly study the effects of blockage of RAAS on inflammation, future studies may explore different strategies by, for example, simultaneously acting on the ACE and the AT1 angiotensin receptors.

Aldosterone and Ang II complementary stimulate ENaC activity during systemic salt restriction

Dietary salt intake controls ENaC activity via renin‐angiotensin‐aldosterone system (RAAS) and aldosterone is considered to be a key modulator. However, experimental evidence suggests possible involvement of other RAAS components (such as Ang II) in ENaC regulation additively to aldosterone. Using patch‐clamp electrophysiology in split‐opened distal nephrons, we demonstrate that Ang II, acting via AT1 receptors, acutely stimulates ENaC open probability (Po) and this effect is preserved, when aldosterone levels are clamped high with DOCA. Application of aldosterone does not reproduce the acute stimulatory action of Ang II. Dietary salt restriction (<0.01% Na+ for 7 days) increases both functional ENaC expression (fN) and ENaC Po. Systemic inhibition of mineralocorticoid receptors with spironolactone (7 days) attenuates ENaC activity by decreasing fN, but not Po. Simultaneous treatment with spironolactone and losartan (AT1 receptor antagonist) virtually abolished elevations of ENaC fN and Po by salt restriction. We conclude that Ang II and aldosterone complementary contribute to proper ENaC activation in response to dietary salt restriction, acting primarily on Po and fN, respectively.

Angiotensin II Increases Activity of the Epithelial Na+ Channel (ENaC) in Distal Nephron Additively to Aldosterone

Dietary salt intake controls epithelial Na+ channel (ENaC)-mediated Na+ reabsorption in the distal nephron by affecting status of the renin-angiotensin-aldosterone system (RAAS). Whereas regulation of ENaC by aldosterone is generally accepted, little is known about whether other components of RAAS, such as angiotensin II (Ang II), have nonredundant to aldosterone-stimulatory actions on ENaC. We combined patch clamp electrophysiology and immunohistochemistry in freshly isolated split-opened distal nephrons of mice to determine the mechanism and molecular signaling pathway of Ang II regulation of ENaC. We found that Ang II acutely increases ENaC Po, whereas prolonged exposure to Ang II also induces translocation of α-ENaC toward the apical membrane in situ. Ang II actions on ENaC Po persist in the presence of saturated mineralocorticoid status. Moreover, aldosterone fails to stimulate ENaC acutely, suggesting that Ang II and aldosterone have different time frames of ENaC activation. AT1 but not AT2 receptors mediate Ang II actions on ENaC. Unlike its effect in vasculature, Ang II did not increase [Ca2+]i in split-opened distal nephrons as demonstrated using ratiometric Fura-2-based microscopy. However, application of Ang II to mpkCCDc14 cells resulted in generation of reactive oxygen species, as probed with fluorescent methods. Consistently, inhibiting NADPH oxidase with apocynin abolished Ang II-mediated increases in ENaC Po in murine distal nephron. Therefore, we concluded that Ang II directly regulates ENaC activity in the distal nephron, and this effect complements regulation of ENaC by aldosterone. We propose that stimulation of AT1 receptors with subsequent activation of NADPH oxidase signaling pathway mediates Ang II actions on ENaC.

CURRENT TARGET OF ANTIHYPERTENSIVE THERAPY. DATA FROM CLINICAL TRIALS. PART 1

Arterial hypertension (HT) takes leading position in the structure of morbidity and mortality among the cardiovascular diseases in the economically developed and developing countries of the world. Despite progress in treatment of this disease, a number of people with uncontrolled or resistant HT increases. There is a problem of inefficiency of therapy or lack of patients' adherence to treatment. Therefore, search for new approaches to treatment of HT continues. Current most effective agents for blood pressure control, and possible future antihypertensive agents, are related to groups of agents, which inhibit renin–angiotensin–aldosterone system (RAAS). Novel targets for antihypertensive therapy could include the angiotensin II type 2 and type 1 receptor , neutral endopeptidase, aldosterone synthase, renalase, endothelin receptors, (pro)renin receptors, vaccine against RAAS components. Development of novel agents and approaches to HT therapy is discussed.

CURRENT TARGET OF ANTIHYPERTENSIVE THERAPY. DATA FROM CLINICAL TRIALS. PART 2

Arterial hypertension (HT) takes leading position in the structure of morbidity and mortality among the cardiovascular diseases in the economically developed and developing countries of the world. Despite progress in treatment of this disease, a number of people with uncontrolled or resistant HT increases. There is a problem of inefficiency of therapy or lack of patients' adherence to treatment. Therefore, search for new approaches to treatment of HT continues. Current most effective agents for blood pressure control, and possible future antihypertensive agents, are related to groups of agents, which inhibit renin–angiotensin–aldosterone system (RAAS). Novel targets for antihypertensive therapy could include the angiotensin II type 2 and type 1 receptor , neutral endopeptidase, aldosterone synthase, renalase, endothelin receptors, (pro)renin receptors, vaccine against RAAS components. Development of novel agents and approaches to HT therapy is discussed.

Abnormalities of angiotensin regulation in postural tachycardia syndrome

Postural tachycardia syndrome (POTS) is a disorder characterized by excessive orthostatic tachycardia and significant functional disability. We previously reported that POTS patients have low blood volume and inappropriately low plasma renin activity (PRA) and aldosterone. In this study, we sought to more fully characterize the renin-angiotensin-aldosterone system (RAAS) to gain a better understanding of the pathophysiology of POTS. The purpose of this study was to prospectively assess the plasma levels of angiotensin (Ang) peptides and their relationship to other RAAS components in patients with POTS compared with healthy controls. Heart rate, PRA, Ang I, Ang II, Ang (1-7), and aldosterone were measured in POTS patients (n = 38) and healthy controls (n = 13) while they were consuming a sodium-controlled diet. POTS patients had larger orthostatic increases in heart rate than did controls (52 ± 3 [mean ± SEM] bpm vs 27 ± 6 bpm, P = .001). Plasma Ang II was significantly higher in POTS patients (43 ± 3 pg/mL vs 28 ± 3 pg/mL, P = .006), whereas plasma Ang I and angiotensin 1-7 [Ang-(1-7)] were similar between groups. Despite the twofold increase of Ang II, POTS patients trended to lower PRA levels than did controls (0.9 ± 0.1 ng/mL/h vs 1.6 ± 0.5 ng/mL/h, P = .268) and lower aldosterone levels (4.6 ± 0.8 pg/mL vs 10.0 ± 3.0 pg/mL, P = .111). Estimated angiotensin-converting enzyme-2 (ACE2) activity was significantly lower in POTS patients than in controls (0.25 ± 0.02 vs 0.33 ± 0.03, P = .038). Some patients with POTS have inappropriately high plasma Ang II levels, with low estimated ACE2 activity. We propose that these abnormalities in Ang regulation may play a key role in the pathophysiology of POTS in some patients.

β2-Adrenergic receptor genotype affects the renin-angiotensin-aldosterone system response to the Dietary Approaches to Stop Hypertension (DASH) dietary pattern

Beta(2)-adrenergic receptor (beta2-AR) is a susceptibility locus for hypertension, and polymorphisms at this site relate to salt sensitivity and low plasma renin activity (PRA). The Dietary Approaches to Stop Hypertension (DASH) dietary pattern lowers blood pressure and appears to interact with the renin-angiotensin-aldosterone system (RAAS). We hypothesized that the DASH diet associates with increased RAAS activity, and genotype status at beta2-AR G46A modifies this response. We genotyped participants in the DASH-Sodium study (n = 372) at beta2-AR G46A to determine the association with blood pressure, RAAS components, and consumption of the DASH diet. We used 2-way mixed linear regression and an additive model for all primary analyses. Mean (+/-SEM) PRA was significantly higher in participants in the DASH group than in participants in the control group (0.68 +/- 0.03 compared with 0.54 +/- 0.03 ng x mL(-1) x h(-1), P = 0.002). Serum aldosterone, urinary aldosterone, and urinary potassium concentrations were also significantly higher in the DASH group (P < 0.01 for all). We observed significant gene-diet interactions for changes in systolic blood pressure (SBP) and concentrations of aldosterone and urinary potassium (P for interaction = 0.048, 0.017, and 0.001 for SBP and aldosterone and urinary potassium concentrations, respectively). There was an association between the A allele of beta2-AR G46A and greater blood pressure reduction and blunted aldosterone and PRA responses to the DASH diet. Our results indicate that the DASH diet lowers blood pressure and increases PRA and aldosterone concentrations. There is an association between the G46A polymorphism of beta2-AR and blood pressure and RAAS responses to the DASH diet, which suggests that beta2-AR may be a genetic modifier of DASH-diet responsiveness. This trial was registered at clinicaltrials.gov as NCT00000608.

Endothelin-1 receptor blockade induces upregulation of renin-angiotensin-aldosterone system expression in terms of blood pressure regulation

To compare the level of expression of the renin-angiotensin-aldosterone system (RAAS) in mice with or without the endothelin-1 receptor antagonist bosentan and to examine the potential value in blood pressure regulation. Bosentan (10 mg/kg/d) and placebo were given to two groups of male C57BL/6 mice (n=5) from ages 6 to 12 weeks. The mRNAs of liver, kidney and lung were isolated for Northern blot analysis. A further 15 male C57BL/6 mice were divided into three groups (n=5): mice in group A were given the angiotensin II type 1 receptor blocker valsartan (10 mg/kg/d); mice in group B were given bosentan (10 mg/kg/d); and mice in group C were given both valsartan and bosentan (10 mg/ kg/d for each drug). All mice were administered the drugs from 6 to 12 weeks of age and had their systolic blood pressure (SBP) measured at the end of the drug treatments. Northern blot analysis demonstrated that the expression levels of angiotensinogen in liver (p=0.0126), renin in kidney (p=0.002), and angiotensin-converting enzyme in lung (p=0.0041) were upregulated in mice treated with bosentan. No difference in SBP was found among the groups before drug administration. Six weeks after monotherapy with valsartan, SBP was slightly lowered (126+/-2 vs. 122+/-3 mmHg, p=0.0381). Monotherapy with bosentan also had a small effect on SBP (126+/-2 vs. 122+/-3 mmHg, p=0.0381), whereas dual blockade with valsartan and bosentan significantly lowered SBP (127+/-3 vs. 103+/-3 mmHg, p<0.001). We conclude that RAAS components are upregulated under endothelin blockade. Dual blockade of the RAAS and endothelin system is beneficial for blood pressure control.

Dietary sodium deprivation evokes activation of brain regional neurons and down-regulation of angiotensin II type 1 receptor and angiotensin-convertion enzyme mRNA expression

Previous studies have indicated that the renin-angiotensin-aldosterone system (RAAS) is implicated in the induction of sodium appetite in rats and that different dietary sodium intakes influence the mRNA expression of central and peripheral RAAS components. To determine whether dietary sodium deprivation activates regional brain neurons related to sodium appetite, and changes their gene expression of RAAS components of rats, the present study examined the c-Fos expression after chronic exposure to low sodium diet, and determined the relationship between plasma and brain angiotensin I (ANG I), angiotensin II (ANG II) and aldosterone (ALD) levels and the sodium ingestive behavior variations, as well as the effects of prolonged dietary sodium deprivation on ANG II type 1 (AT1) and ANG II type 2 (AT2) receptors and angiotensin-convertion enzyme (ACE) mRNA levels in the involved brain regions using the method of real-time polymerase chain reaction (PCR). Results showed that the Fos immunoreactivity (Fos-ir) expression in forebrain areas such as subfornical organ (SFO), paraventricular hypothalamic nuclei (PVN), supraoptic nucleus (SON) and organum vasculosum laminae terminalis (OVLT) all increased significantly and that the levels of ANG I, ANG II and ALD also increased in plasma and forebrain in rats fed with low sodium diet. In contrast, AT1, ACE mRNA in PVN, SON and OVLT decreased significantly in dietary sodium depleted rats, while AT2 mRNA expression did not change in the examined areas. These results suggest that many brain areas are activated by increased levels of plasma and/or brain ANG II and ALD, which underlies the elevated preference for hypertonic salt solution after prolonged exposure to low sodium diet, and that the regional AT1 and ACE mRNA are down-regulated after dietary sodium deprivation, which may be mediated by increased ANG II in plasma and/or brain tissue.

Effects of long‐term transdermal hormone replacement therapy on the renin–angiotensin– aldosterone system, plasma bradykinin levels and blood pressure in normotensive postmenopausal women

This study was designed to investigate the effects of 24-month long-term transdermal hormone replacement therapy (HRT) on the circulating levels of components of the renin-angiotensin-aldosterone system (RAAS) and bradykinin, blood pressure (BP) and lipid profile in normotensive postmenopausal women (PMW). Twenty-two normotensive PMW were randomized to receive transdermal HRT (continuous 17-beta estradiol patch at 36 microg/day plus cyclic oral medroxyprogesterone acetate 2.5 mg/day for 12 days/month) (n = 12) or control (n = 10). The plasma renin activity (PRA), serum angiotensin-converting enzyme (ACE) activity, plasma angiotensin (Ang) I, Ang II, aldosterone, bradykinin, and BP were measured before, and 12 and 24 months after, the start of the HRT. In the HRT group, the diastolic BP and mean BP were significantly decreased at 12 and 24 months (both P < 0.05) after the start of therapy, however, no significant change of the systolic BP was noted during the study period. No changes in the RAAS components or lipid profile were noted in either group. The plasma bradykinin levels were significantly reduced at 12 (P < 0.05) and 24 months (P < 0.01), while no changes were observed in the control group. More than 12 months of long-term transdermal HRT kept diastolic BP, mean BP and plasma bradykinin levels decreased in normotensive PMW, without influencing any of the components of the RAAS. This therapy may allow optimal blood pressure control and prevent elevation of the cardiovascular risk.

The emerging role of ACE2 in physiology and disease

The renin–angiotensin–aldosterone system (RAAS) is a key regulator of systemic blood pressure and renal function and a key player in renal and cardiovascular disease. However, its (patho)physiological roles and its architecture are more complex than initially anticipated. Novel RAAS components that may add to our understanding have been discovered in recent years. In particular, the human homologue of ACE (ACE2) has added a higher level of complexity to the RAAS. In a short period of time, ACE2 has been cloned, purified, knocked‐out, knocked‐in; inhibitors have been developed; its 3D structure determined; and new functions have been identified. ACE2 is now implicated in cardiovascular and renal (patho)physiology, diabetes, pregnancy, lung disease and, remarkably, ACE2 serves as a receptor for SARS and NL63 coronaviruses. This review covers available information on the genetic, structural and functional properties of ACE2. Its role in a variety of (patho)physiological conditions and therapeutic options of modulation are discussed. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Gene Polymorphisms of the Renin-Angiotensin-Aldosterone System and Angiotensin II Type 1-Receptor Activating Antibodies in Renal Rejection

Steroid refractory acute rejection (SRAR) is a major vital factor in renal transplantation recipients. The pathogenesis of SRAR may involve both immune and non-immune mechanisms. A decreased renal allograft function has also been associated with increased activity of renin-angiotensin-aldosterone system (RAS), which may be genetically determined. A total 206 renal transplant recipients, 116 males and 90 females, were included. The effects of gene polymorphisms of the four components of RAS including angiotensinogen (AGT), angiotensin-converting enzyme (ACE), angiotensin type 1 receptor (AT1R), and aldosterone synthase (CYP11B2) were investigated in 19 cases of renal transplant patients with SRAR. The association between SRAR and the activating antibodies targeting the AT1R were also investigated. Genotyping was performed for the M235T-AGT, the I/D-ACE, the A1166C-AT1R, and the -344T/C-CYP11B2 gene polymorphisms using polymerase chain reaction. Our results showed that renal allograft recipients with SRAR had significantly higher occurrences of the DD genotype of ACE and CC genotype of AT1R than recipients without SRAR. The other genetic polymorphisms of the RAS were not associated with SRAR. Activating antibodies targeting the AT1R were detected in the sera from 14 SRAR victims with malignant hypertension and without anti-HLA antibodies. This study provides evidence that determination before transplantation of the polymorphism of the gene encoding components of RAS may help identify patients who are at risk for SRAR. The detection of the antibodies of AT1R may contribute to the prevention of SRAR.

Blockade of the Renin-Angiotensin-Aldosterone System: Effects on Hypertensive Target Organ Damage

The renin-angiotensin-aldosterone system (RAAS) plays a relevant role not only in the pathophysiology of essential hypertension, but also in the development of hypertensive target organ damage. Different drugs acting on RAAS components are now available: angiotensin-converting-enzyme (ACE) inhibitors, angiotensin II AT1 receptors blockers (ARBs), non-selective and selective aldosterone antagonists. The review will focus on their effects on hypertensive organ damage. In fact, apart from the well known efficacy in reducing blood pressure, all these drugs have been demonstrated to protect against target organ damage, reversing or preventing its development. The main issues addressed will be: effects of the RAAS blockade on heart and kidney disease, protective action against arterial wall damage, with a focus on the endothelial protection. The comparison among ACE inhibitors, ARBs and aldosterone antagonists will be discussed, with specific reference to different class and/or drug effects and to the results of few studies evaluating the effects of combination therapy with different drugs blocking the RAAS.

Adducin and microalbuminuria: a complex association

Adducin and microalbuminuria: a complex association

Effects of aldosterone on cardiac local rennin- angiotensin -aldosterone system: an important role of cardiac fibroblasts

Recent studies showed cardiac local renin-angiotensin-aldosterone system (RAAS) play a pivotal role in pathophysiology in heart, and spironolactone, which is aldosterone blockade has beneficial effects on prognosis of patients with heart failure. We sought to determine how aldosterone, which is distal component of RAAS, acts on cardiac local RAAS using cultured cardiac myocytes and fibroblasts, and whether spironolactone inhibits these effects. Cultured cardiocytes were prepared from 1- or 2-day-old neonatal Sprague-Dawley rats by digestion with collagenase and pancratin. Cardiac myocytes and fibroblasts were separated by Percoll method and cultivated. After starvation period, aldosterone was added to culture medium and later, total RNA was extracted from the cells. mRNAs of renin, angiotensiongen, and ACE were semiquantified by RT-PCR. Basal mRNA expressions of renin, angiotensinogen, and ACE were observed in both cadiac myocytes and fibroblasts. After 48 hours of aldosterone stimulation, ACE mRNA was significantly upregulated in cardiac fibroblasts, however, gene expressions of renin and angiotensinogen were unchanged in cardiac fibroblasts and none of these RAAS component was upregulated in cardiac myocytes. Moreover, spironolactone completely inhibited aldosterone-induced augmentation of ACE gene expression in cardiac fibroblasts.In conclusion, our data support an idea that cardiac local RAAS has positive feedback system, which mainly depends on cardiac fibroblasts, and clinical beneficial effects of spironolactone may be partly due to blockage of positive feedback circuit.

Renin–Angiotensin–Aldosterone System Loci and Multilocus Interactions in Young‐Onset Essential Hypertension

Objective: Renin–angiotensin–aldosterone system component genes have been associated to essential hypertension. Thus, we studied the association of singe locus or multilocus interactions with young‐onset essential hypertension. Setting and Design: This is a case‐control study based on a population sample of adolescent at an inner city. Participants: We studied 54 adolescents with hypertension and 121 age‐matched normotensives, recruited from a high‐school student population of 934 interviewed individuals. Methods: Resting blood pressure was measured on three different days and normalized (Z‐score) by sex and age. Genotypes of ACE (I/D) angiotensinogen (T174M and M235T), AT1R (A1166C), and CYP11B2 (C‐344T) were determined by PCR/RFLP or ASO. Results: Although genotype frequencies were not different in both groups, we found a significant dominant effect of ACE D and angiotensinogen 235T alleles on normalized systolic arterial blood pressure in males. This effect was confirmed by sib‐pair linkage analysis taking normalized blood pressure as a quantitative trait. We independently analyzed multilocus interactions in normotensive and hypertensive adolescents searching for multiple locus deviation from Hardy–Weinberg or linkage equilibrium. We found that from 63 multilocus combinations, 4 deviated significantly from equilibrium in hypertensive adolescents but none in the normotensives. Deviations from equilibrium may indicate that the combination of alleles at different loci affects susceptibility or resistance to the disease. Conclusion: In addition to the angiotensin‐converting enzyme (ACE) and angiotensinogen (AGT) gene variants, gene–gene interactions may be important causative factors in a complex disease such as young‐onset essential hypertension.

Endothelial dysfunction in cardiovascular diseases

markdownabstractThe measurement of endothelial function might predict the presence of CAD in patients. Therefore, we tested in part I of this thesis the applicability of peripheral endothelial dysfunction as a measurement for the presence of coronary artery disease (CAD) in symptomatic patients. We showed that endothelial function measurement with peripheral arterial tonometry is a heterogeneous measurement with poor correlation with traditional measurements. Moreover, the measurement failed to predict revascularization within one year. Therefore, in spite of the pathophysiological basis of endothelial dysfunction in CAD, no evidence was found for peripheral endothelial function measurement as a diagnostic tool to detect clinically relevant CAD. Since patient studies to unravel underlying disease processes are usually hampered by limited measurements because of ethical concerns; experimental disease models in animals can enhance our understanding of the pathogenesis of CAD. Therefore, we studied and developed an animal model of CAD, in which we studied the coronary microcirculation. We demonstrated that small coronary arteries showed functional alterations in vitro in the process of early systemic atherosclerosis development in diabetic pigs on a high fat diet, reflecting an altered coronary microvascular balance. This balance changed over time during CAD progression and was shown to be a systemic process. In part II of this thesis, we studied endothelial dysfunction in relation to percutaneous coronary interventions. We demonstrated that specific first generation drug-eluting stents impair the microcirculation in the distal perfusion area of the stent. Also, the latest percutaneous coronary intervention, the bioresorbable vascular scaffold, was studied with regard to endothelial dysfunction. We demonstrated that specifically in diabetic pigs coronary conduit segments proximal and distal to the scaffold edges showed reduced endothelium-dependent vasodilation. In part III of this thesis, we studied endothelial dysfunction related to diabetes mellitus and the renin-angiotensin-aldosterone system (RAAS). To examine which RAAS components are activated in diabetes, we examined these components in both plasma and urine samples of both diabetic and non-diabetic patients with hypertension. We proved that urinary renin more closely reflects renal RAAS activity than urinary angiotensinogen or aldosterone. The relation between an overactive RAAS, DM and endothelial dysfunction was further studied with use of diabetic, hypertensive, transgenic rats with high prorenin, renin and (pro)renin receptor levels. We evaluated whether the renin inhibitor aliskiren, with or without the (pro)renin receptor antagonist HRP, improved the disturbed vascular function and end organ disease of diabetic transgenic rats. Endothelial dysfunction with an altered vasomotor balance was demonstrated to be present within this animal model and we demonstrated that treatment with the renin inhibitor aliskiren reversed the vascular effects, as well as end organ disease. This indicates that renin inhibition can at least partially reverse the altered endothelial balance of diabetes and an overactive RAAS. Remarkably, when blocking the (pro)renin receptor on top of renin inhibition, the beneficial effects disappeared.