Angiotensin-(1-7) potentiates the hypotensive effect of bradykinin in conscious rats

Angiotensin-(1-7) and Central Control of Cardiometabolic Outcomes: Implications for Obesity Hypertension

Hypertension is a leading independent risk factor for the development of cardiovascular disease, the leading cause of death globally. Importantly, the prevalence of hypertension is positively correlated with obesity, with obesity-related hypertension being difficult to treat due to a lack of current guidelines in this population as well as limited efficacy and adverse off-target effects of currently available antihypertensive therapeutics. This highlights the need to better understand the mechanisms linking hypertension with obesity to develop optimal therapeutic approaches. In this regard, the renin-angiotensin system, which is dysregulated in both hypertension and obesity, is a prime therapeutic target. While research and therapies have typically focused on the deleterious angiotensin II axis of the renin-angiotensin system, emerging evidence shows that targeting the protective angiotensin-(1-7) axis also improves cardiovascular and metabolic functions in animal models of obesity hypertension. While the precise mechanisms involved remain under investigation, in addition to peripheral actions, evidence exists to support a role for the central nervous system in the beneficial cardiometabolic effects of angiotensin-(1-7). This review will highlight emerging translational studies exploring the cardiovascular and metabolic regulatory actions of angiotensin-(1-7), with an emphasis on its central actions in brain regions including the brainstem and hypothalamus. An improved understanding of the central mechanisms engaged by angiotensin-(1-7) to regulate cardiovascular and metabolic functions may provide insight into the potential of targeting this hormone as a novel therapeutic approach for obesity-related hypertension.

Interaction of Angiotensin-(1-7) with kinins in the kidney circulation: Role of B1 receptors

Changes in renal hemodynamics impact renal function during physiological and pathological conditions. In this context, renal vascular resistance (RVR) is regulated by components of the Renin-Angiotensin System (RAS) and the Kallikrein-Kinin System (KKS). However, the interaction between these vasoactive peptides on RVR is still poorly understood. Here, we studied the crosstalk between angiotensin-(1-7) and kinins on RVR. The right kidneys of Wistar rats were isolated and perfused in a closed-circuit system. The perfusion pressure and renal perfusate flow were continuously monitored. Ang-(1-7) (1.0-25.0 nM) caused a sustained, dose-dependent reduction of relative RVR (rRVR). This phenomenon was sensitive to 10 nM A-779, a specific Mas receptor (MasR) antagonist. Bradykinin (BK) promoted a sustained and transient reduction in rRVR at 1.25 nM and 125 nM, respectively. The transient effect was abolished by 4 μM des-Arg9-Leu8-bradykinin (DALBK), a specific kinin B1 receptor (B1R) antagonist. Accordingly, des-Arg9-bradykinin (DABK) 1 μM (a B1R agonist) increased rRVR. Interestingly, pre-perfusion of Ang-(1-7) changed the sustained reduction of rRVR triggered by 1.25 nM BK into a transient effect. On the other hand, pre-perfusion of Ang-(1-7) primed and potentiated the DABK response, this mechanism being sensitive to A-779 and DALBK. Binding studies performed with CHO cells stably transfected with MasR, B1R, and kinin B2 receptor (B2R) showed no direct interaction between Ang-(1-7) with B1R or B2R. In conclusion, our findings suggest that Ang-(1-7) differentially modulates kinin's effect on RVR in isolated rat kidneys. These results help to expand the current knowledge regarding the crosstalk between the RAS and KKS complex network in RVR.

Effects of oral HPΒCD-angiotensin-(1-7) supplementation on recreational mountain bike athletes: a crossover study

BACKGROUND

Supplementation with Angiotensin-(1-7) [(Ang-1-7)] has received considerable attention due to its possible ergogenic effects on physical performance. The effects of a single dose of Ang-(1-7) on the performance of mountain bike (MTB) athletes during progressive load tests performed until the onset of voluntary fatigue have previously been demonstrated. This study tested the effects of Ang-(1-7) in two different exercise protocols with different metabolic demands: aerobic (time trial) and anaerobic (repeated sprint).

METHODS

Twenty one male recreational athletes were given capsules containing an oral formulation of HPβCD-Ang-(1-7) (0.8 mg) and HPβCD-placebo (only HPβCD) over a 7-day interval; a double-blind randomized crossover design was used. Physical performance was examined using two protocols: a 20-km cycling time trial or 4 × 30-s repeated all-out sprints on a leg cycle ergometer. Data were collected before and after physical tests to assess fatigue parameters, and included lactate levels, and muscle activation during the sprint protocol as evaluated by electromyography (EMG); cardiovascular parameters: diastolic and systolic blood pressure and heart rate; and performance parameters, time to complete (time trial), maximum power and mean power (repeated sprint).

RESULTS

Supplementation with an oral formulation of HPβCD-Ang-(1-7) reduced basal plasma lactate levels and promoted the maintenance of plasma glucose levels after repeated sprints. Supplementation with HPβCD-Ang-(1-7) also increased baseline plasma nitrite levels and reduced resting diastolic blood pressure in a time trial protocol. HPβCD-Ang-(1-7) had no effect on the time trial or repeat sprint performance, or on the EMG recordings of the vastus lateralis and vastus medialis.

CONCLUSIONS

Supplementation with HPβCD-Ang-(1-7) did not improve physical performance in time trial or in repeated sprints; however, it promoted the maintenance of plasma glucose and lactate levels after the sprint protocol and at rest, respectively. In addition, HPβCD-Ang-(1-7) also increased resting plasma nitrite levels and reduced diastolic blood pressure in the time trial protocol.

TRIAL REGISTRATION

RBR-2nbmpbc, registered January 6th, 2023. The study was prospectively registered.

Cirrhotic portal hypertension: From pathophysiology to novel therapeutics

Portal hypertension and bleeding from gastroesophageal varices is the major cause of morbidity and mortality in patients with cirrhosis. Portal hypertension is initiated by increased intrahepatic vascular resistance and a hyperdynamic circulatory state. The latter is characterized by a high cardiac output, increased total blood volume and splanchnic vasodilatation, resulting in increased mesenteric blood flow. Pharmacological manipulation of cirrhotic portal hypertension targets both the splanchnic and hepatic vascular beds. Drugs such as angiotensin converting enzyme inhibitors and angiotensin II type receptor 1 blockers, which target the components of the classical renin angiotensin system (RAS), are expected to reduce intrahepatic vascular tone by reducing extracellular matrix deposition and vasoactivity of contractile cells and thereby improve portal hypertension. However, these drugs have been shown to produce significant off-target effects such as systemic hypotension and renal failure. Therefore, the current pharmacological mainstay in clinical practice to prevent variceal bleeding and improving patient survival by reducing portal pressure is non-selective -blockers (NSBBs). These NSBBs work by reducing cardiac output and splanchnic vasodilatation but most patients do not achieve an optimal therapeutic response and a significant proportion of patients are unable to tolerate these drugs. Although statins, used alone or in combination with NSBBs, have been shown to improve portal pressure and overall mortality in cirrhotic patients, further randomized clinical trials are warranted involving larger patient populations with clear clinical end points. On the other hand, recent findings from studies that have investigated the potential use of the blockers of the components of the alternate RAS provided compelling evidence that could lead to the development of drugs targeting the splanchnic vascular bed to inhibit splanchnic vasodilatation in portal hypertension. This review outlines the mechanisms related to the pathogenesis of portal hypertension and attempts to provide an update on currently available therapeutic approaches in the management of portal hypertension with special emphasis on how the alternate RAS could be manipulated in our search for development of safe, specific and effective novel therapies to treat portal hypertension in cirrhosis.

Retinal angiotensin II and angiotensin-(1-7) response to hyperglycemia and an intervention with captopril

Hypothesis:

Hyperglycemia decreases angiotensin-(1-7), the endogenous counter-regulator of angiotensin II in the retina.

Materials and methods:

The distribution and levels of retinal angiotensin II (Ang II) and angiotensin-(1-7) (Ang-(1-7)) were evaluated by confocal imaging and quantitative immunohistochemistry during the development of streptozotocin-induced diabetes in rats.

Results:

In the nondiabetic eye, Ang II was localized to the endfeet of Müller cells, extending into the cellular processes of the inner plexiform layer and inner nuclear layer; Ang-(1-7) showed a wider distribution, extending from the foot plates of the Müller cells to the photoreceptor layer. Eyes from diabetic animals showed a higher intensity and extent of Ang II staining compared with nondiabetic eyes, but lower intensity with a reduced distribution of Ang-(1-7) immunoreactivity. Treatment of the diabetic animals with the angiotensin-converting enzyme inhibitor (ACEI) captopril showed a reduced intensity of Ang II staining, whereas increased intensity and distribution were evident with Ang-(1-7) staining.

Conclusions:

These studies reveal that pharmacological inhibition with ACEIs may provide a specific intervention for the management of the diabetes-induced decline in retinal function, reversing the profile of the endogenous angiotensin peptides closer to the normal condition.

Kallikrein-kinin system as the dominant mechanism to counteract hyperactive renin-angiotensin system

The renin-angiotensin system (RAS) generates, maintains, and makes worse hypertension and cardiovascular diseases (CVDs) through its biologically active component angiotensin II (Ang II), that causes vasoconstriction, sodium retention, and structural alterations of the heart and the arteries. A few endogenous vasodilators, kinins, natriuretic peptides, and possibly angiotensin (1-7), exert opposite actions and may provide useful therapeutic agents. As endothelial autacoids, the kinins are potent vasodilators, active natriuretics, and protectors of the endothelium. Indeed, the kallikrein-kinin system (KKS) is considered the dominant mechanism for counteracting the detrimental effects of the hyperactive RAS. The 2 systems, RAS and KKS, are controlled by the angiotensin-converting enzyme (ACE) that generates Ang II and inactivates the kinins. Inhibitors of ACE can reduce the impact of Ang II and potentiate the kinins, thus contributing to restore the cardiovascular homeostasis. In the last 20 years, ACE-inhibitors (ACE-Is) have become the drugs of first choice for the treatments of the major CVDs. ACE-Is not only reduce blood pressure, as sartans also do, but by protecting and potentiating the kinins, they can reduce morbidity and mortality and improve the quality of life for patients with CVDs. This paper provides a brief review of the literature on this topic.

Bradykinin -induced vasodilatation: Role of age, ACE1-inhibitory peptide, mas- and bradykinin receptors

Bradykinin exerts its vascular actions via two types of receptors, the non-constitutively expressed bradykinin receptor type 1 (BR1) and the constitutive type 2 receptor (BR2). Bradykinin-induced vasorelaxation is age-dependent, a phenomenon related to the varying amounts of BR1 and BR2 in the vasculature. Isoleucine-proline-proline (Ile-Pro-Pro), a bioactive tripeptide, lowers elevated blood pressure and improves impaired endothelium-dependent vasorelaxation in hypertensive rats. It inhibits angiotensin converting enzyme 1 (ACE1). Other mechanisms of action have also been postulated. The aims of the study were to clarify the underlying mechanisms of the age-dependency of bradykinin-induced vasodilatation such as the roles of the two bradykinin receptors, the mas-receptor and synergism with Ile-Pro-Pro. The vascular response studies were conducted using mesenteric artery and aorta rings from normotensive 6 wk. (young) and 22 wk. (old) Wistar rats. Cumulative dosing of acetylcholine, bradykinin and angiotensin(1-7) (Ang(1-7))were tested in phenylephrine-induced vasoconstriction with or without 10min pre-incubation with antagonists against BR1-, BR2- or mas-receptors, Ang(1-7) or ACE1-inhibitors captopril and Ile-Pro-Pro. The bradykinin-induced vasorelaxation in vitro was age-dependent and it was improved by pre-incubation with Ile-Pro-Pro, especially in old rats with endothelial dysfunction. The mas-receptor antagonist, D-Pro₇-Ang(1-7) abolished bradykinin-induced relaxation totally. Interestingly, BR1 and BR2 antagonists only slightly reduced bradykinin-induced vasorelaxation, as an evidence for the involvement of other mechanisms in addition to receptor activation. In conclusion, bradykinin-induced vasorelaxation was age-dependent and Ile-Pro-Pro improved it. Mas receptor antagonist abolished relaxation while bradykinin receptor antagonist only slightly reduced it, suggesting that bradykinin-induced vasorelaxation is regulated also by other mechanisms than the classical BR1/BR2 pathway.

Angiotensin-(1-7) Selectively Induces Relaxation and Modulates Endothelium-Dependent Dilation in Mesenteric Arteries of Salt-Fed Rats

This study investigated the acute effects of angiotensin-(1-7) and AVE0991 on active tone and vasodilator responses to bradykinin and acetylcholine in isolated mesenteric arteries from Sprague-Dawley rats fed a high-salt (HS; 4% NaCl) versus a normal salt (NS; 0.4% NaCl) diet. Angiotensin-(1-7) and AVE0991 elicited relaxation, and angiotensin-(1-7) unmasked vasodilator responses to bradykinin in arteries from HS-fed rats. These effects of angiotensin-(1-7) and AVE0991 were inhibited by endothelium removal, A779, PD123319, HOE140 and L-NAME. Angiotensin-(1-7) also restored the acetylcholine-induced relaxation that was suppressed by the HS diet. Vasodilator responses to bradykinin and acetylcholine in the presence of angiotensin-(1-7) were mimicked by captopril and the AT2 receptor agonist CGP42112 in arteries from HS-fed rats. Thus, in contrast to salt-induced impairment of vascular relaxation in response to vasodilator stimuli, angiotensin-(1-7) induces endothelium-dependent and NO-mediated relaxation, unmasks bradykinin responses via activation of mas and AT2 receptors, and restores acetylcholine-induced vasodilation in HS-fed rats. AT2 receptor activation and angiotensin-converting enzyme (ACE) inhibition shared the ability of angiotensin-(1-7) to enhance bradykinin and acetylcholine responses in HS-fed rats. These findings suggest a therapeutic potential for mas and/or AT2 receptor activation and ACE inhibition in restoring endothelial function impaired by elevated dietary salt intake or other pathological conditions.

The role of Ang (1-7) in mediating the chronic hypotensive effects of losartan in normal rats

Hypothesis

The following studies were designed to test the hypothesis that Ang (1-7) contributes to the chronic hypotensive effects of the angiotensin II AT1-receptor antagonist, losartan, in normal rats.

Introduction

We have previously shown a chronic, hypotensive response to the AT1-receptor antagonist, losartan, in normotensive rats. The mechanism of this response is not completely understood. Previous studies by others have demonstrated a role for Ang (1-7) in the beneficial antihypertensive effects of angiotensin-converting enzyme (ACE) inhibition. This is thought to be due to vasodilatory effects of increased levels of Ang (1-7) during ACE inhibition. Since it has now been shown that Ang (1-7) levels are also increased during AT1 antagonism, we designed experiments to test the hypothesis above.

Materials and methods

Sprague-Dawley rats were instrumented with venous catheters and radiotelemetric pressure transducers and commenced on a normal (0.4%) NaCl diet. Arterial pressure responses were measured in rats treated with losartan (10 mg/kg/day) (LOS rats, n=8) and compared with those treated with losartan and the Ang (1-7) antagonist, A779 (24 µg/kg/hour) (A779/LOS rats, n=11) for 10 days.

Results

By day 7 of treatment, mean arterial pressure had dropped by 27±1 mmHg in LOS rats, in contrast with a decrease of only 21±2 mmHg in A779/LOS rats. This attenuated response in rats treated with A779 became more prominent and continued through day 10 of losartan treatment.

Conclusion

These results support the hypothesis that the chronic hypotensive effects of losartan in normal rats are mediated in part through the actions of Ang (1-7).

ACE2 and vasoactive peptides: novel players in cardiovascular/renal remodeling and hypertension

The renin-angiotensin system (RAS) is a key component of cardiovascular physiology and homeostasis due to its influence on the regulation of electrolyte balance, blood pressure, vascular tone and cardiovascular remodeling. Deregulation of this system contributes significantly to the pathophysiology of cardiovascular and renal diseases. Numerous studies have generated new perspectives about a noncanonical and protective RAS pathway that counteracts the proliferative and hypertensive effects of the classical angiotensin-converting enzyme (ACE)/angiotensin (Ang) II/angiotensin type 1 receptor (AT1R) axis. The key components of this pathway are ACE2 and its products, Ang-(1-7) and Ang-(1-9). These two vasoactive peptides act through the Mas receptor (MasR) and AT2R, respectively. The ACE2/Ang-(1-7)/MasR and ACE2/Ang-(1-9)/AT2R axes have opposite effects to those of the ACE/Ang II/AT1R axis, such as decreased proliferation and cardiovascular remodeling, increased production of nitric oxide and vasodilation. A novel peptide from the noncanonical pathway, alamandine, was recently identified in rats, mice and humans. This heptapeptide is generated by catalytic action of ACE2 on Ang A or through a decarboxylation reaction on Ang-(1-7). Alamandine produces the same effects as Ang-(1-7), such as vasodilation and prevention of fibrosis, by interacting with Mas-related GPCR, member D (MrgD). In this article, we review the key roles of ACE2 and the vasoactive peptides Ang-(1-7), Ang-(1-9) and alamandine as counter-regulators of the ACE-Ang II axis as well as the biological properties that allow them to regulate blood pressure and cardiovascular and renal remodeling.

Analysis of erectile responses to bradykinin in the anesthetized rat

The kallikrein-kinin system is expressed in the corpus cavernosa, and bradykinin (BK) relaxes isolated corpora cavernosal strips. However, erectile responses to BK in the rat have not been investigated in vivo. In the present study, responses to intracorporal (ic) injections of BK were investigated in the anesthetized rat. BK, in doses of 1-100 μg/kg ic, produced dose-related increases in intracavernosal pressure (ICP) and dose-related deceases in mean arterial pressure (MAP). When decreases in MAP were prevented by intravenous injections of angiotensin II (Ang II), increases in ICP, in response to BK, were enhanced. Increases in ICP, ICP/MAP ratio, and area under the curve and decreases in MAP in response to BK were inhibited by the kinin B2 receptor antagonist HOE-140 and enhanced by the angiotensin-converting enzyme (ACE) inhibitor captopril and by Ang-(1-7). Increases in ICP, in response to BK, were not attenuated by the nitric oxide (NO) synthase inhibitor (N(ω)-nitro-L-arginine methyl ester) or the soluble guanylate cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) but were attenuated by the cyclooxygenase inhibitor, sodium meclofenamate. Decreases in MAP were not attenuated by either inhibitor. These data suggest that erectile responses are mediated by kinin B2 receptors and modulated by decreases in MAP. These data indicate that ACE is important in the inactivation of BK and that erectile and hypotensive responses are independent of NO in the penis or the systemic vascular bed. Erectile responses to cavernosal nerve stimulation are not altered by BK or HOE-140, suggesting that BK and B2 receptors do not modulate nerve-mediated erectile responses under physiologic conditions. These data suggest that erectile responses to BK are mediated, in part, by the release of cyclooxygenase products.

Non-canonical signalling and roles of the vasoactive peptides angiotensins and kinins

GPCRs (G-protein-coupled receptors) are among the most important targets for drug discovery due to their ubiquitous expression and participation in cellular events under both healthy and disease conditions. These receptors can be activated by a plethora of ligands, such as ions, odorants, small ligands and peptides, including angiotensins and kinins, which are vasoactive peptides that are classically involved in the pathophysiology of cardiovascular events. These peptides and their corresponding GPCRs have been reported to play roles in other systems and under pathophysiological conditions, such as cancer, central nervous system disorders, metabolic dysfunction and bone resorption. More recently, new mechanisms have been described for the functional regulation of GPCRs, including the transactivation of other signal transduction receptors and the activation of G-protein-independent pathways. The existence of such alternative mechanisms for signal transduction and the discovery of agonists that can preferentially trigger one signalling pathway over other pathways (called biased agonists) have opened new perspectives for the discovery and development of drugs with a higher specificity of action and, therefore, fewer side effects. The present review summarizes the current knowledge on the non-canonical signalling and roles of angiotensins and kinins.

A systematic review to investigate whether Angiotensin-(1-7) is a promising therapeutic target in human heart failure

Context. Heart failure (HF) is a common condition causing much morbidity and mortality despite major advances in pharmacological and device therapies. Preclinical data suggest a cardioprotective role of Angiotensin-(1-7) in animal models of HF. Objective. Perform a systematic review on the effects of Angiotensin-(1-7) on humans, focusing on HF. Results. 39 studies were included in the review (4 in human HF and (35) in non-HF patients). There is only one intervention study on 8 patients with human HF, using Angiotensin-(1-7), with forearm blood flow (FBF) as the endpoint. Angiotensin-(1-7) caused no significant effect on FBF in this HF study but caused vasodilation in 3 out of 4 non-HF studies. In one other non-HF study, Angiotensin-(1-7) infusion led to a significant increase in blood pressure in normal men; however, effects were <0.03% that of angiotensin II. Cardioprotective effects seen in non-HF studies include for instance beneficial actions against atherosclerosis and myocardial fibrosis. Conclusions. The main finding of our systematic review is that Angiotensin-(1-7) plays an important cardioprotective role in HF in animals and in patients without heart failure. More research is required to test the hypothesis that Angiotensin-(1-7) benefits patients with heart failure.

Targeting the 'Janus face' of the B2-bradykinin receptor

INTRODUCTION

Kinins are main active mediators of the kallikrein-kinin system (KKS) via bradykinin type 1 inducible (B1R) and type 2 constitutive (B2R) receptors. B2R mediates most physiological bradykinin (BK) responses, including vasodilation, natriuresis, NO, prostaglandins release.

AREAS COVERED

The article summarizes knowledge on kinins, B2R signaling and biological functions; highlights crosstalks between B2R and renin-angiotensin system (RAS). The double role (Janus face) in physiopathology, namely the beneficial protection of the endothelium, which forms the basis for the therapeutical utilization of B2 receptor agonists, on the one side, and the involvement of B2R in inflammation or infection diseases and in pain mechanisms, which justifies the use of B2R antagonists, on the other side, is extensively analyzed.

EXPERT OPINION

For decades, the B2R has been unconsciously activated during angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) treatments. Whether direct B2R targeting with stable agonists could bring additional therapeutic benefit to RAS inhibition should be investigated. Efficacy, established in experimental models, should be confirmed by translational studies in cardiovascular pathologies, glaucoma, Duchenne cardiopathy and during brain cancer therapy. The other face of B2R is targeted by antagonists already approved to treat hereditary angioedema. The use of antagonists could be extended to other angioedema and efficacy tested against acute pain and inflammatory diseases.

Effects of enalapril on the expression of cardiac angiotensin-converting enzyme and angiotensin-converting enzyme 2 in spontaneously hypertensive rats

BACKGROUND

The discovery of angiotensin-converting enzyme 2 (ACE2) has greatly modified understanding of the renin-angiotensin system (RAS).

AIMS

To investigate the cardiac expression of ACE2 and ACE in spontaneously hypertensive rats (SHRs) and the effects of enalapril on them.

METHODS

Fifteen SHRs were randomly assigned to two groups: an SHR control group (n=7), treated with vehicle; and an enalapril group (n=8), treated with enalapril (15 mg/kg/day). After 4 weeks of treatment, the rats were killed and the left ventricular tissue was dissected. Reverse transcription-polymerase chain reaction and Western blot protein staining were performed to detect expression of ACE2 and ACE messenger ribonucleic acid (mRNA) and protein. Ten Wistar Kyoto rats (WKYs) served as the normotensive control group, which were treated with vehicle.

RESULTS

Compared with in normotensive WKYs, cardiac expression of ACE mRNA and protein in SHRs was increased (1.68±0.34 vs. 0.33±0.12, P<0.05 and 1.21±0.14 vs. 0.71±0.11, P<0.05, respectively), whereas cardiac expression of ACE2 mRNA and protein was decreased (0.50±0.15 vs. 1.16±0.24, P<0.05 and 0.71±0.24 vs. 1.22±0.14, P<0.05, respectively). After treatment with enalapril, the levels of ACE mRNA and protein were decreased (0.44±0.19 vs. 1.68±0.34, P<0.01 and 0.87±0.13 vs. 1.21±0.14, P<0.05, respectively), the level of ACE2 mRNA was increased (1.77±0.49 vs. 0.50±0.15, P<0.05) but the level of ACE2 protein remained unchanged.

CONCLUSIONS

In SHRs, the expression of cardiac ACE was remarkably increased, whereas ACE2 was notably decreased. Reduction of ACE and elevation of ACE2 might be one of the mechanisms underlying the antihypertensive function of enalapril.

Angiotensin-converting enzyme 2, angiotensin-(1-7) and Mas: new players of the renin-angiotensin system

Angiotensin (Ang)-(1-7) is now recognized as a biologically active component of the renin-angiotensin system (RAS). Ang-(1-7) appears to play a central role in the RAS because it exerts a vast array of actions, many of them opposite to those attributed to the main effector peptide of the RAS, Ang II. The discovery of the Ang-converting enzyme (ACE) homolog ACE2 brought to light an important metabolic pathway responsible for Ang-(1-7) synthesis. This enzyme can form Ang-(1-7) from Ang II or less efficiently through hydrolysis of Ang I to Ang-(1-9) with subsequent Ang-(1-7) formation by ACE. In addition, it is now well established that the G protein-coupled receptor Mas is a functional binding site for Ang-(1-7). Thus, the axis formed by ACE2/Ang-(1-7)/Mas appears to represent an endogenous counterregulatory pathway within the RAS, the actions of which are in opposition to the vasoconstrictor/proliferative arm of the RAS consisting of ACE, Ang II, and AT(1) receptor. In this brief review, we will discuss recent findings related to the biological role of the ACE2/Ang-(1-7)/Mas arm in the cardiovascular and renal systems, as well as in metabolism. In addition, we will highlight the potential interactions of Ang-(1-7) and Mas with AT(1) and AT(2) receptors.

The interaction of AGT and NOS3 gene polymorphisms with conventional risk factors increases predisposition to hypertension

Renin-angiotensin and kallikrein-kinin systems are interconnected, regulating blood pressure homeostasis. We have demonstrated the interactions among polymorphisms of the angiotensinogen (AGT) and endothelial nitric oxide synthase (NOS3) genes and conventional risk factors affecting the hypertension occurrence. Individuals were recruited (n=192) and classified into hypertensive (HG; n=140) and normotensive (NG; n=52) groups. The genotypic distribution of the Met235Thr (AGT) and Glu298Asp (NOS3) polymorphisms demonstrated that both are independent risk factors of hypertension (p=0.02 and p=0.008, respectively). The concomitant presence of these polymorphisms in the HG group was significantly different (p=0.001) from the NG. Both gene polymorphisms presented an additive effect for the unfavourable alleles T and A, respectively, and 95% of the double mutant homozygotes were classified into the HG. Specific interactions among certain conventional factors and the presence of at least one unfavourable allele presented significant odds towards hypertension. Blood pressure homeostasis was affected by genetic polymorphisms conditioned by the T and A alleles of the AGT and NOS3 genes, respectively, which acted independently. However, their interaction with smoking, sedentariness, age and total cholesterol may have increased the predisposition to hypertension, which may explain most of the hypertension cases.

Angiotensin-converting enzyme inhibition, but not AT(1) receptor blockade, in the solitary tract nucleus improves baroreflex sensitivity in anesthetized transgenic hypertensive (mRen2)27 rats

Transgenic hypertensive (mRen2)27 rats overexpress the murine Ren2 gene and have impaired baroreflex sensitivity (BRS) for control of the heart rate. Removal of endogenous angiotensin (Ang)-(1-7) tone using a receptor blocker does not further lower BRS. Therefore, we assessed whether blockade of Ang II with a receptor antagonist or combined reduction in Ang II and restoration of endogenous Ang-(1-7) levels with Ang-converting enzyme (ACE) inhibition will improve BRS in these animals. Bilateral solitary tract nucleus (nTS) microinjections of the AT(1) receptor blocker, candesartan (CAN, 24 pmol in 120 nl, n=9), or a peptidic ACE inhibitor, bradykinin (BK) potentiating nonapeptide (Pyr-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro; BPP9α, 9 nmol in 60 nl, n=12), in anesthetized male (mRen2)27 rats (15-25 weeks of age) show that AT(1) receptor blockade had no significant effect on BRS, whereas microinjection of BPP9α improved BRS over 60-120 min. To determine whether Ang-(1-7) or BK contribute to the increase in BRS, separate experiments using the Ang-(1-7) receptor antagonist D-Ala(7)-Ang-(1-7) or the BK antagonist HOE-140 showed that only the Ang-(1-7) receptor blocker completely reversed the BRS improvement. Thus, acute AT(1) blockade is unable to reverse the effects of long-term Ang II overexpression on BRS, whereas ACE inhibition restores BRS over this same time frame. As the BPP9α potentiation of BK actions is a rapid phenomenon, the likely mechanism for the observed delayed increase in BRS is through ACE inhibition and elevation of endogenous Ang-(1-7).

Renin-angiotensin system may trigger kidney damage in NOD mice

Diabetic nephropathy is a complication of diabetes and one of the main causes of end-stage renal disease. A possible causal link between renin-angiotensin aldosterone system (RAAS) and diabetes is widely recognized but the mechanisms by which the RAAS may lead to this complication remains unclear. The aim of this study was to evaluate angiotensin-I converting enzyme (ACE) activity and expression in numerous tissues, especially kidney, of non-obese diabetic mouse. Kidney, lung, pancreas, heart, liver and adrenal tissues from diabetic and control female NOD mice were homogenized for measurement of ACE activity, SDS-PAGE and Western blotting for ACE and ACE2, immunohistochemistry for ACE and angiotensins I, II and 1-7 and bradykinin quantification. ACE activity was higher in kidney, lung and adrenal tissue of diabetic mice compared with control mice. In pancreas, activity was decreased in the diabetic group. Western blotting analysis indicated that both groups presented ACE isoforms with molecular weights of 142 and 69 kDa and a decrease in ACE2 protein expression. Angiotensin concentrations were not altered within groups, although bradykinin levels were higher in diabetic mice. The immunohistochemical study in kidney showed an increase in tubular ACE expression. Our results show that the RAAS is affected by diabetes and the elevated ACE/ACE2 ratio may contribute to renal damage.

Physiology of Kidney Renin

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

Angiotensin-(1-7) stimulates high atrial pacing-induced ANP secretion via Mas/PI3-kinase/Akt axis and Na+/H+ exchanger

Angiotensin-(1-7) [ANG-(1-7)], one of the bioactive peptides produced in the renin-angiotensin system, plays a pivotal role in cardiovascular physiology by providing a counterbalance to the function of ANG II. Recently, it has been considered as a potential candidate for therapeutic use in the treatment of various types of cardiovascular diseases. The aim of the present study is to explain the modulatory role of ANG-(1-7) in atrial natriuretic peptide (ANP) secretion and investigate the functional relationship between two peptides to induce cardiovascular effects using isolated perfused beating rat atria and a cardiac hypertrophied rat model. ANG-(1-7) (0.01, 0.1, and 1 muM) increased ANP secretion and ANP concentration in a dose-dependent manner at high atrial pacing (6.0 Hz) with increased cGMP production. However, at low atrial pacing (1.2 Hz), ANG-(1-7) did not cause changes in atrial parameters. Pretreatment with an antagonist of the Mas receptor or with inhibitors of phosphatidylinositol 3-kinase (PI3K), protein kinase B (Akt), or nitric oxide synthase blocked the augmentation of high atrial pacing-induced ANP secretion by ANG-(1-7). A similar result was observed with the inhibition of the Na(+)/H(+) exchanger-1 and Ca(2+)/calmodulin-dependent kinase II (CaMKII). ANG-(1-7) did not show basal intracellular Ca(2+) signaling in quiescent atrial myocytes. In an in vivo study using an isoproterenol-induced cardiac hypertrophy animal model, an acute infusion of ANG-(1-7) increased the plasma concentration of ANP by twofold without changes in blood pressure and heart rate. A chronic administration of ANG-(1-7) increased the plasma ANP level and attenuated isoproterenol-induced cardiac hypertrophy. The antihypertrophic effect was abrogated by a cotreatment with the natriuretic peptide receptor-A antagonist. These results suggest that 1) ANG-(1-7) increased ANP secretion at high atrial pacing via the Mas/PI3K/Akt pathway and the activation of Na(+)/H(+) exchanger-1 and CaMKII and 2) ANG-(1-7) decreased cardiac hypertrophy which might be mediated by ANP.

Relationship between angiotensin-(1-7) and angiotensin II correlates with hemodynamic changes in human liver cirrhosis

AIM: To measure circulating angiotensins at different stages of human cirrhosis and to further evaluate a possible relationship between renin angiotensin system (RAS) components and hemodynamic changes.

METHODS: Patients were allocated into 4 groups: mild-to-moderate liver disease (MLD), advanced liver disease (ALD), patients undergoing liver transplantation, and healthy controls. Blood was collected to determine plasma renin activity (PRA), angiotensin (Ang) I, Ang II, and Ang-(1-7) levels using radioimmunoassays. During liver transplantation, hemodynamic parameters were determined and blood was simultaneously obtained from the portal vein and radial artery in order to measure RAS components.

RESULTS: PRA and angiotensins were elevated in ALD when compared to MLD and controls (P < 0.05). In contrast, Ang II was significantly reduced in MLD. Ang-(1-7)/Ang II ratios were increased in MLD when compared to controls and ALD. During transplantation, Ang II levels were lower and Ang-(1-7)/Ang II ratios were higher in the splanchnic circulation than in the peripheral circulation (0.52 ± 0.08 vs 0.38 ± 0.04, P < 0.02), whereas the peripheral circulating Ang II/Ang I ratio was elevated in comparison to splanchnic levels (0.18 ± 0.02 vs 0.13 ± 0.02, P < 0.04). Ang-(1-7)/Ang II ratios positively correlated with cardiac output (r = 0.66) and negatively correlated with systemic vascular resistance (r = -0.70).

CONCLUSION: Our findings suggest that the relationship between Ang-(1-7) and Ang II may play a role in the hemodynamic changes of human cirrhosis.

The sweeter side of ACE2: physiological evidence for a role in diabetes

Diabetes mellitus is a growing problem in all parts of the world. Both clinical trials and animal models of type I and type II diabetes have shown that hyperactivity of angiotensin-II (Ang-II) signaling pathways contribute to the development of diabetes and diabetic complications. Of clinical relevance, blockade of the renin-angiotensin system prevents new-onset diabetes and reduces the risk of diabetic complications. Angiotensin-converting enzyme (ACE) 2 is a recently discovered mono-carboxypeptidase and the first homolog of ACE. It is thought to inhibit Ang-II signaling cascades mostly by cleaving Ang-II to generate Ang-(1-7), which effects oppose Ang-II and are mediated by the Mas receptor. The enzyme is present in the kidney, liver, adipose tissue and pancreas. Its expression is elevated in the endocrine pancreas in diabetes and in the early phase during diabetic nephropathy. ACE2 is hypothesized to act in a compensatory manner in both diabetes and diabetic nephropathy. Recently, we have shown the presence of the Mas receptor in the mouse pancreas and observed a reduction in Mas receptor immuno-reactivity as well as higher fasting blood glucose levels in ACE2 knockout mice, indicating that these mice may be a new model to study the role of ACE2 in diabetes. In this review we will examine the role of the renin-angiotensin system in the physiopathology and treatment of diabetes and highlight the potential benefits of the ACE2/Ang-(1-7)/Mas receptor axis, focusing on recent data about ACE2.

Angiotensin converting enzyme 2 in the kidney

1

Angiotensin converting enzyme 2 (ACE2) is an important homeostatic component of the renin angiotensin system (RAS). ACE2 both degrades the vasoconstrictor, angiotensin II and generates the potent vasodilator peptide, angiotensin 1–7. These actions counterbalance those of ACE.

2

ACE2 is highly expressed in the healthy kidney, particularly in the proximal tubules, where it colocalizes with ACE and angiotensin receptors.

3

Kidney disease and subtotal nephrectomy is associated with a reduction in renal ACE2 expression, possibly facilitating the damaging effects of angiotensin II in the failing kidney. Acquired or genetic ACE2 deficiency also appears to exacerbate renal damage and albuminuria in experimental models, supporting this hypothesis.

4

ACE2 also has an important role in blood pressure control. Many models of hypertension are associated with reduced ACE2 expression. Although ACE2 KO animals are normotensive, in states associated with activation of the RAS, ACE2 overexpression improves blood pressure control and reduces angiotensin responsiveness.

Effects of intracerebroventricular infusion of angiotensin-(1-7) on bradykinin formation and the kinin receptor expression after focal cerebral ischemia-reperfusion in rats

Accumulating evidence suggests that the angiotensin-(1-7) [Ang-(1-7)], is an active member of the brain renin-angiotensin system (RAS). We evaluated the possibility that intracerebroventricular (ICV, lateral ventricle) infusion of exogenous Ang-(1-7) could participate in the potentiation of bradykinin (BK) release and the kinin receptor expression in ischemic brain parenchyma after focal cerebral ischemia-reperfusion in rats. The middle cerebral artery occlusion (MCAO) and sham-operated models were prepared, continuously administrated with Ang-(1-7) or artificial cerebrospinal fluid (aCSF) by implanted Alzet osmotic minipumps into lateral cerebral ventricle after reperfusion in male Sprague-Dawley (SD) rats. Experimental animals were divided into sham-operated group (sham+aCSF), aCSF treatment group (MCAO+aCSF) and Ang-(1-7) treatment groups [MCAO+Ang-(1-7)] at low (1 pmol/0.5 microl/h), medium (100 pmol/0.5 microl/h) or high (10 nmol/0.5 microl/h) dose levels. Cerebral infarction resulted in a significant increase of BK formation from 3 h to 6 h compared with sham-operated group after reperfusion, whereas medium- and high-dose Ang-(1-7) infusion markedly enhanced BK levels from 6 h to 48 h after reperfusion. Medium- and high-dose Ang-(1-7) infusion markedly increased kinin B(2) receptor mRNA and protein expression, whereas only high-dose Ang-(1-7) infusion induced upregulating the expression of B(1) receptor. Low-dose Ang-(1-7) infusion did not modify both the kinin B(1) and B(2) receptor expression compared with aCSF treatment group after focal cerebral ischemia-reperfusion at each time point. The finding might indicate complex interactions between Ang-(1-7) and kallikrein-kinin system in the CNS after focal cerebral ischemia-reperfusion in rats.

Tityus serrulatus Hypotensins: a new family of peptides from scorpion venom

Using a proteomic approach, a new structural family of peptides was put in evidence in the venom of the yellow scorpion Tityus serrulatus. Tityus serrulatus Hypotensins (TsHpt) are random-coiled linear peptides and have a similar bradykinin-potentiating peptide (BPP) amino acid signature. TsHpt-I (2.7kDa), the first member of this family, was able to potentiate the hypotensive effects of bradykinin (BK) in normotensive rats. Using the C-terminal of this peptide as a template, a synthetic analog peptide (TsHpt-I([17-25])) was designed to held the BK-potentiating effect. A relevant hypotensive effect, independent on BK, was also observed on both TsHpt (native and synthetic). To better evaluate this hypotensive effect, we examined the vasorelaxation of aortic rings from male Wistar rats and the peptides were able to induce endothelium-dependent vasorelaxation dependent on NO release. Both TsHpt could not inhibit ACE activity. These peptides appear to exert their anti-hypertensive effect through NO-dependent and ACE-independent mechanisms.

New angiotensins

Accumulation of a large body of evidence during the past two decades testifies to the complexity of the renin–angiotensin system (RAS). The incorporation of novel enzymatic pathways, resulting peptides, and their corresponding receptors into the biochemical cascade of the RAS provides a better understanding of its role in the regulation of cardiovascular and renal function. Hence, in recent years, it became apparent that the balance between the two opposing effector peptides, angiotensin II and angiotensin-(1-7), may have a pivotal role in determining different cardiovascular pathophysiologies. Furthermore, our recent studies provide evidence for the functional relevance of a newly discovered rat peptide, containing two additional amino acid residues compared to angiotensin I, first defined as proangiotensin-12 [angiotensin-(1-12)]. This review focuses on angiotensin-(1-7) and its important contribution to cardiovascular function and growth, while introducing angiotensin-(1-12) as a potential novel angiotensin precursor.

Enalapril treatment corrects the reduced response to bradykinin in diabetes increasing the B2 protein expression

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the effect of enalapril on the reduced response of bradykinin and on the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems, in an insulin-resistance model of diabetes. For the above purpose, the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. In n-STZ diabetic rats, enalapril treatment restored the reduced response to BK but not the potentiation of BK by Ang-(1-7) present in non-diabetic rats. The restorative effect of enalapril was observed at a dose that did not correct the altered parameters induced by diabetes such as hyperglycemia, glicosuria, insulin resistance but did reduce the high blood pressure levels of n-SZT diabetic rats. There was no difference in mRNA and protein expressions of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Enalapril treatment increased the B2 kinin receptor expression. From our data, we conclude that in diabetes enalapril corrects the impaired BK response probably by increasing the expression of B2 receptors. The lack of potentiation of BK by Ang-(1-7) is not corrected by this agent.

Angiotensin receptor subtype mediated physiologies and behaviors: new discoveries and clinical targets

The renin-angiotensin system (RAS) mediates several classic physiologies including body water and electrolyte homeostasis, blood pressure, cyclicity of reproductive hormones and sexual behaviors, and the regulation of pituitary gland hormones. These functions appear to be mediated by the angiotensin II (AngII)/AT(1) receptor subtype system. More recently, the angiotensin IV (AngIV)/AT(4) receptor subtype system has been implicated in cognitive processing, cerebroprotection, local blood flow, stress, anxiety and depression. There is accumulating evidence to suggest an inhibitory influence by AngII acting at the AT(1) subtype, and a facilitory role by AngIV acting at the AT(4) subtype, on neuronal firing rate, long-term potentiation, associative and spatial learning, and memory. This review initially describes the biochemical pathways that permit synthesis and degradation of active angiotensin peptides and three receptor subtypes (AT(1), AT(2) and AT(4)) thus far characterized. There is vigorous debate concerning the identity of the most recently discovered receptor subtype, AT(4). Descriptions of classic and novel physiologies and behaviors controlled by the RAS are presented. This review concludes with a consideration of the emerging therapeutic applications suggested by these newly discovered functions of the RAS.

ACE2: a new target for cardiovascular disease therapeutics

The discovery of angiotensin-converting enzyme 2 (ACE2) in 2000 is an important event in the renin-angiotensin system (RAS) story. This enzyme, an homolog of ACE, hydrolyzes angiotensin (Ang) I to produce Ang-(1-9), which is subsequently converted into Ang-(1-7) by a neutral endopeptidase and ACE. ACE2 releases Ang-(1-7) more efficiently than its catalysis of Ang-(1-9) by cleavage of Pro(7)-Phe(8) bound in Ang II. Thus, the major biologically active product of ACE2 is Ang-(1-7), which is considered to be a beneficial peptide of the RAS cascade in the cardiovascular system. This enzyme has 42% identity with the catalytic domain of ACE, is present in most cardiovascular-relevant tissues, and is an ectoenzyme as ACE. Despite these similarities, ACE2 is distinct from ACE. Since it is a monocarboxypeptidase, it has only 1 catalytic site and is insensitive to ACE inhibitors. As a result, ACE2 is a central enzyme in balancing vasoconstrictor and proliferative actions of Ang II with vasodilatory and antiproliferative effects of Ang-(1-7). In this review, we will summarize the role of ACE2 in the cardiovascular system and discuss the importance of ACE2-Ang-(1-7) axis in the control of normal cardiovascular physiology and ACE2 as a potential target in the development of novel therapeutic agents for cardiovascular diseases.

On the mechanism of coronary vasodilation induced by angiotensin-(1-7) in the isolated guinea pig heart

Various mechanisms have been postulated to be involved in angiotensin-(1-7)-induced endothelium-dependent vasodilation. Here, we characterized the vasodilator action of angiotensin-(1-7) in the isolated guinea pig heart. Angiotensin-(1-7) (1-10 nmol, bolus) induced dose-dependent increase in the coronary flow. The coronary vasodilation induced by angiotensin-(1-7) was significantly reduced by the nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (L-NAME) (100 microM) and abolished by a B(2) receptor antagonist, icatibant (100 nM). Coronary vasodilation induced by bradykinin (3 pmol, bolus) was inhibited by L-NAME and icatibant to similar extent as that induced by angiotensin-(1-7). Neither the selective AT(2) angiotensin receptor antagonist, PD123319 (1 microM), nor the antagonist of a putative angiotensin-(1-7) receptors, [D-alanine-7]-angiotensin-(1-7) (A-779, 1 microM), influenced the response to angiotensin-(1-7). In conclusion, in the isolated guinea pig heart angiotensin-(1-7) induces coronary vasodilation that is mediated by endogenous bradykinin and subsequent stimulation of nitric oxide release through endothelial B(2) receptors. In contrast to other vascular beds, AT(2) angiotensin receptors and specific angiotensin-(1-7) receptors do not appear involved in angiotensin-(1-7)-induced coronary vasodilation in the isolated guinea pig heart.

Angiotensin-(1-7): pharmacology and new perspectives in cardiovascular treatments

Many advances have been made in the cardiovascular field in the last several decades. Among them is the progress completed to date on the heptapeptide member of the renin-angiotensin system (RAS), angiotensin-(1-7) [Ang-(1-7)]. The peptide's beneficial actions against pathophysiological processes, such as cardiac arrhythmia, heart failure, hypertension, renal disease, preeclampsia, and even cancer are continuously being uncovered. This review encompasses the pharmacology of Ang-(1-7) and expounds upon the peptide's potential as a therapeutic agent against pathological processes both within and outside the cardiovascular continuum.

Angiotensin-(1–7) stimulates the phosphorylation of JAK2, IRS-1 and Akt in rat heart in vivo: role of the AT1 and Mas receptors

Angiotensin (ANG) II exerts a negative modulation on insulin signal transduction that might be involved in the pathogenesis of hypertension and insulin resistance. ANG-(1–7), an endogenous heptapeptide hormone formed by cleavage of ANG I and ANG II, counteracts many actions of ANG II. In the current study, we have explored the role of ANG-(1–7) in the signaling crosstalk that exists between ANG II and insulin. We demonstrated that ANG-(1–7) stimulates the phosphorylation of Janus kinase 2 (JAK2) and insulin receptor substrate (IRS)-1 in rat heart in vivo. This stimulating effect was blocked by administration of the selective ANG type 1 (AT1) receptor blocker losartan. In contrast to ANG II, ANG-(1–7) stimulated cardiac Akt phosphorylation, and this stimulation was blunted in presence of the receptor Mas antagonist A-779 or the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin. The specific JAK2 inhibitor AG-490 blocked ANG-(1–7)-induced JAK2 and IRS-1 phosphorylation but had no effect on ANG-(1–7)-induced phosphorylation of Akt, indicating that activation of cardiac Akt by ANG-(1–7) appears not to involve the recruitment of JAK2 but proceeds through the receptor Mas and involves PI3K. Acute in vivo insulin-induced cardiac Akt phosphorylation was inhibited by ANG II. Interestingly, coadministration of insulin with an equimolar mixture of ANG II and ANG-(1–7) reverted this inhibitory effect. On the basis of our present results, we postulate that ANG-(1–7) could be a positive physiological contributor to the actions of insulin in heart and that the balance between ANG II and ANG-(1–7) could be relevant for the association among insulin resistance, hypertension, and cardiovascular disease.

Different responses to angiotensin-(1-7) in young, aged and diabetic rabbit corpus cavernosum

We evaluated the ability of angiotensin-(1-7) [Ang-(1-7)] to produce relaxation of the corpus cavernosum of New Zealand White rabbits. The reactivity of corpus cavernosal strips isolated from young rabbits (8-10 months old) was assessed in organ-bath chambers. Cumulative concentration response curves for Ang-(1-7), angiotensin II (Ang II), carbachol and sodium nitroprusside (SNP) were established. Ang-(1-7) (10(-12) to 10(-5)M) produced a concentration-dependent relaxation of the corpus cavernosal strips with a pD(2) value of 9.8+/-0.3. Ang-(1-7)-induced maximal relaxant response was reduced by 48+/-2%, 57+/-3% and 76+/-2% in the presence of A-779 (10(-6)M), a selective Ang-(1-7) receptor (AT(1-7)) antagonist, nitro-l-arginine methyl ester (l-NAME) (10(-4)M), an inhibitor of nitric oxide (NO) synthase, or iberiotoxin (5 x 10(-8)M), an inhibitor of calcium-activated potassium (BK) channels, respectively. In contrast, Ang II-induced contraction was increased in the presence of A-779. Carbachol-, SNP- and Ang-(1-7)-induced relaxations were significantly reduced whereas Ang-II induced contraction was significantly increased in the cavernosum strips from older (18-24 months old) and diabetic rabbits compared to the young. Pre-incubation of the cavernosum strips obtained from young, older or diabetic rabbits with Ang-(1-7) resulted in a significant attenuation of Ang II-induced contraction. In conclusion, these results demonstrate that Ang-(1-7) can produce nitric oxide-dependent relaxation of the corpus cavernosum through activation of AT(1-7) and BK channels. Older and diabetic animals showed impaired Ang-(1-7)-mediated relaxation suggesting that aging and diabetes related erectile dysfunction (ED) may be partly due to decreased Ang-(1-7)-mediated relaxation of the corpus cavernosum. Acute pre-incubation with Ang-(1-7) was effective in attenuating Ang II-induced contraction of rabbit corpus cavernosum suggesting that the possible role of Ang-(1-7) in treatment of ED should be investigated.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

Lack of potentiation of bradykinin by angiotensin-(1-7) in a type 2 diabetes model: role of insulin

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems in an insulin resistance model of diabetes, and the effect of insulin on it. For this the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. Though capable of potentiating BK in non-diabetic rats, Ang-(1-7) did not potentiate BK in n-STZ rats. Chronic but not acute insulin treatment restored the potentiation. This restorative effect of insulin was abolished by a K+ channel blocker (tetraethylammonium), by nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester) and by a cyclooxygenase inhibitor (indomethacin). On the other hand, Na(+)-,K(+)-ATPase inhibition (by ouabain) did not abolish the effect of insulin. There was no difference in mRNA and protein expression of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Insulin treatment did not alter the kinin receptor expression. Our data allow us to conclude that diabetes impaired the interaction between BK and Ang-(1-7) and that insulin restores it. The restoring effect of insulin depends on membrane hyperpolarization, nitric oxide release and cyclooxygenease metabolites but not Na+K+-ATPase. Alteration of kinin receptor expression might not be involved in the restoring effect of insulin on the potentiation of BK by Ang-(1-7).

Angiotensin-(1-7) potentiates responses to bradykinin but does not change responses to angiotensin I

Angiotensin-(1-7) (Ang-(1-7)), a bioactive peptide in the renin-angiotensin system, has counterregulatory actions to angiotensin II (Ang II). However, the mechanism by which Ang-(1-7) enhances vasodepressor responses to bradykinin (BK) is not well understood. In the present study, the effects of Ang-(1-7) on responses to BK, BK analogs, angiotensin I (Ang I), and Ang II were investigated in the anesthetized rat. The infusion of Ang-(1-7) (55 pmol/min i.v.) enhanced decreases in systemic arterial pressure in response to i.v. injections of BK and the BK analogs [Hyp3, Tyr(Me)8]-bradykinin (HT-BK) and [Phe8psi (CH2-NH) Arg9]-bradykinin (PA-BK) without altering pressor responses to Ang I or II, or depressor responses to acetylcholine and sodium nitroprusside. The angiotensin-converting enzyme (ACE) inhibitor enalaprilat enhanced responses to BK and the BK analog HT-BK without altering responses to PA-BK and inhibited responses to Ang I. The potentiating effects of Ang-(1-7) and enalaprilat on responses to BK were not attenuated by the Ang-(1-7) receptor antagonist A-779. Ang-(1-7)- and ACE inhibitor-potentiated responses to BK were attenuated by the BK B2 receptor antagonist Hoe 140. The cyclooxygenase inhibitor sodium meclofenamate had no significant effect on responses to BK or Ang-(1-7)-potentiated BK responses. These results suggest that Ang-(1-7) potentiates responses to BK by a selective B2 receptor mechanism that is independent of an effect on Ang-(1-7) receptors, ACE, or cyclooxygenase product formation. These data suggest that ACE inhibitor-potentiated responses to BK are not mediated by an A-779-sensitive mechanism and are consistent with the hypothesis that enalaprilat-induced BK potentiation is due to decreased BK inactivation.

On the role of prolyl oligopeptidase in health and disease

Prolyl oligopeptidase (POP) is a serine peptidase which digests small peptide-like hormones, neuroactive peptides, and various cellular factors. Therefore, this peptidase has been implicated in many physiological processes as well as in some psychiatric disorders, most probably through interference in inositol cycle. Intense research has been performed to elucidate, on the one hand, the basic structure, ligand binding, and kinetic properties of POP, and on the other, the pharmacology of its inhibitors. There is fairly strong evidence of in vivo importance of POP on substance P, arginine vasopressin, thyroliberin and gonadoliberin metabolism. However, information about the biological relevance of POP is not yet conclusive. Evidence regarding the physiological role of POP is lacking, which is surprising considering that peptidase inhibitors have been exploited for drug development, some of which are currently in clinical trials as memory enhancers for the aged and in a variety of neurological disorders. Here we review the recent progress on POP research and evaluate the relevance of the peptidase in the metabolism of various neuropeptides. The recognition of novel forms and relatives of POP may improve our understanding of how this family of proteins functions in normal and in neuropathological conditions.

The role of angiotensin(1-7) in renal vasculature of the rat

OBJECTIVE

Angiotensin(1-7) is an active component of the renin-angiotensin-aldosterone system. Its exact role in renal vascular function is unclear. We therefore studied the effects of angiotensin(1-7) on the renal vasculature in vitro and in vivo.

METHODS

Isolated small renal arteries were studied in an arteriograph system by constructing concentration-response curves to angiotensin II, without and with angiotensin(1-7). In isolated perfused kidneys, the response of angiotensin II on renal vascular resistance was measured without and with angiotensin(1-7). The influence of angiotensin(1-7) on angiotensin II-induced glomerular afferent and efferent constriction was assessed with intravital microscopy in vivo under anaesthesia. In freely moving rats, we studied the effect of angiotensin(1-7) on angiotensin II-induced reduction of renal blood flow with an electromagnetic flow probe.

RESULTS

Angiotensin(1-7) alone had no effect on the renal vasculature in any of the experiments. In vitro, angiotensin(1-7) antagonized angiotensin-II-induced constriction of isolated renal arteries (9.71 +/- 1.21 and 3.20 +/- 0.57%, for control and angiotensin(1-7) pre-treated arteries, respectively; P < 0.0005). In isolated perfused kidneys, angiotensin(1-7) reduced the angiotensin II response (100 +/- 16.6 versus 72.6 +/- 15.6%, P < 0.05) and shifted the angiotensin II dose-response curve rightward (pEC50, 6.69 +/- 0.19 and 6.26 +/- 0.12 for control and angiotensin(1-7) pre-treated kidneys, respectively; P < 0.05). Angiotensin(1-7), however, was devoid of effects on angiotensin-II-induced constriction of glomerular afferent and efferent arterioles and on angiotensin-II-induced renal blood flow reduction in freely moving rats in vivo.

CONCLUSION

Angiotensin(1-7) antagonizes angiotensin II in renal vessels in vitro, but does not appear to have a major function in normal physiological regulation of renal vascular function in vivo.

Pharmacological Effects of AVE 0991, a Nonpeptide Angiotensin-(1?7) Receptor Agonist

In the last 20 years, our understanding of the physiopathology of the renin-angiotensin system (RAS) has expanded dramatically. Basic and clinical studies showed that this system includes several other components in addition to renin, angiotensin (Ang) II, an-giotensin-converting enzyme (ACE), and Ang II receptors. One of the most interesting new members of RAS is the heptapeptide Ang-(1-7). Many in vitro and in vivo studies have proven that this peptide plays several beneficial effects in the cardiovascular system, which are often opposite to the effects elicited by the main component of the RAS, Ang II. In addition, the recent discovery of the main enzyme involved in the Ang-(1-7) production, ACE2 and the description of the Ang-(1-7) receptor Mas reinforced the biological relevance of this peptide. These findings raised the possibility to develop new drugs based on the ACE2-Ang-(1-7)-Mas axis and directed to cardiovascular and -related diseases. The development of AVE 0991, a nonpeptide Ang-(1-7) receptor Mas agonist, represents an important step for exploration of the effects of Ang-(1-7) and testing of its potential as a cardiovascular drug. Among advantages of this compound in comparison with Ang-(1-7) is the fact that it is orally active and is expected to be resistant to proteolytic enzymes, circumventing an important problem associated with the use of peptides. This article briefly reviews in vitro and in vivo cardiovascular and renal effects of AVE 0991. Moreover, we are pointing to the evidence that ACE2-Ang-(1-7)-Mas axis may represent a putative target for the development of new cardiovascular drugs.

Pressor responses to alligator Angiotensin I and some analogs in the spectacled caiman (Caiman crocodilus)

Discovery of the chemical structure of alligator (Alligator mississipiensis) [Asp(1), Val(5), Ala(9)]-Angiotensin I (ANG I) has permitted the investigation of cardiovascular responses to this peptide and its analogs in spectacled caimans (Caiman crocodilus), close relatives of alligators. ANG I and [Asp(1), Val(5)]- Angiotensin II (ANG II) i.v. gave dose-dependent increases in mean arterial pressure but there was no pressor response to [Val(4)]-ANG III (ANG III). Pressor responses to a series of doses of ANG II were compared with a range of doses of norepinephrine (NE) and epinephrine (E) which were found to be only about 1/100 as potent as ANG II on a molar basis. The replacement of d-leu(10)in the alligator ANG I molecule with l-leu(10) almost stopped its conversion to ANG II and attenuated the pressor response. [Asp(1), Val(5), Ala(9)]-ANG I (1-9), and ANG (1-7) both failed to increase arterial blood pressure, even at the relatively high non-physiological test dose of 194pmolkgbw(-1) i.v. Captopril blocked angiotensin converting enzyme (ACE) and prevented the pressor response to ANG I whereas the mammalian AT(1) inhibitor Losartan attenuated, but did not completely block the pressor response to ANG II. These are the first experiments which test the cardiovascular responses to alligator ANG I and its analogues in any crocodilian species.