Cardiovascular effects of small peptides of the renin angiotensin system.

The renin-angiotensin system (RAS) is a unique hormonal cascade which is composed by multiple enzymes and effector peptides. Recently, new peptides presenting biological activity have been discovered, increasing the complexity of the RAS Here, we evaluated the effects of small peptides of the RAS in coronary bed of rats. Firstly, we examined the direct effect of small angiotensinergic peptides [Angiotensin (Ang) -(1-5), Ang-(1-4) Ang-(1-3), and Ang-(1-2)] in coronary vessels. Noteworthy, it was observed that Ang-(1-4), Ang-(1-3), and Ang-(1-2) caused a significant reduction in pressure perfusion. Because Ang-(1-2) was the smallest peptide tested and presented the major effect, we decided to investigate its mechanisms of action. The effect of Ang-(1-2) was partially dependent on the Mas receptor, nitric oxide release and angiotensin-converting enzyme. Importantly, Ang-(1-2) reduced the blood pressure of Wistar rats and SHR Interestingly, SHR presented a more pronounced decrease in blood pressure levels than Wistar rats. Altogether, these data showed that angiotensinergic small peptides hold biological activities in coronary bed of rats.

Cardiovascular effects of angiotensin A: a novel peptide of the renin-angiotensin system.

INTRODUCTION: Angiotensin (Ang) A was first identified in human plasma and it differs from Ang II in Ala(1) instead of Asp(1). Here, we hypothesized that the actions of this peptide might explain, at least partially, the limited effects of AT1R antagonists in certain cardiovascular diseases. MATERIALS AND METHODS: The effects of Ang A and Ang II on blood pressure (BP) and heart function were compared. Importantly, participation of AT1R in these effects was evaluated. Furthermore, the effects of these two peptides on ischemia/reperfusion arrhythmias and involvement of calcium in these effects were investigated. RESULTS: Administration of increasing doses of these peptides caused elevations in BP at comparable magnitude. AT1R blockade completely abolished these effects. The actions of these peptides in cardiac function were quite similar although the effects of Ang A were only partially blocked by losartan. Interestingly, Ang II elicited an increase in the duration of ischemia/reperfusion arrhythmias while Ang A had no effect on cardiac rhythm during reperfusion. In accordance, differently to Ang II, Ang A did not induce any significant effect on calcium transient during baseline and ischemic stress conditions. CONCLUSIONS: These data suggest that the existence of alternative peptides of the renin-angiotensin system (RAS) might contribute to the limited effects of angiotensin receptor blockers (ARBs) in certain pathophysiological circumstances.

Angiotensin-converting enzyme 2 activation improves endothelial function.

Diminished release and function of endothelium-derived nitric oxide coupled with increases in reactive oxygen species production is critical in endothelial dysfunction. Recent evidences have shown that activation of the protective axis of the renin-angiotensin system composed by angiotensin-converting enzyme 2, angiotensin-(1-7), and Mas receptor promotes many beneficial vascular effects. This has led us to postulate that activation of intrinsic angiotensin-converting enzyme 2 would improve endothelial function by decreasing the reactive oxygen species production. In the present study, we tested 1-[[2-(dimetilamino)etil]amino]-4-(hidroximetil)-7-[[(4-metilfenil)sulfonil]oxi]-9H-xantona-9 (XNT), a small molecule angiotensin-converting enzyme 2 activator, on endothelial function to validate this hypothesis. In vivo treatment with XNT (1 mg/kg per day for 4 weeks) improved the endothelial function of spontaneously hypertensive rats and of streptozotocin-induced diabetic rats when evaluated through the vasorelaxant responses to acetylcholine/sodium nitroprusside. Acute in vitro incubation with XNT caused endothelial-dependent vasorelaxation in aortic rings of rats. This vasorelaxation effect was attenuated by the Mas antagonist D-pro7-Ang-(1-7), and it was reduced in Mas knockout mice. These effects were associated with reduction in reactive oxygen species production. In addition, Ang II-induced reactive oxygen species production in human aortic endothelial cells was attenuated by preincubation with XNT. These results showed that chronic XNT administration improves the endothelial function of hypertensive and diabetic rat vessels by attenuation of the oxidative stress. Moreover, XNT elicits an endothelial-dependent vasorelaxation response, which was mediated by Mas. Thus, this study indicated that angiotensin-converting enzyme 2 activation promotes beneficial effects on the endothelial function and it is a potential target for treating cardiovascular disease.

Oral administration of an angiotensin-converting enzyme 2 activator ameliorates diabetes-induced cardiac dysfunction.

We evaluated the hypothesis that activation of endogenous angiotensin-converting enzyme (ACE) 2 would improve cardiac dysfunction induced by diabetes. Ten days after diabetes induction (streptozotocin, 50 mg/kg, i.v.), male Wistar rats were treated with the ACE2 activator 1-[[2-(dimethylamino)ethyl]amino]-4-(hydroxymethyl)-7-[[(4-methylphenyl)sulfonyl]oxy]-9H-xanthen-9-one (XNT, 1 mg/kg/day, gavage) or saline (control) for 30 days. Echocardiography was performed to analyze the cardiac function and kinetic fluorogenic assays were used to determine cardiac ACE and ACE2 activities. Cardiac ACE2, ACE, Mas receptor, AT(1) receptor, AT(2) receptor and collagen types I and III mRNA and ACE2, ACE, Mas, AT(1) receptor, AT(2) receptor, ERK1/2, Akt, AMPK-α and AMPK-ß(1) protein were measured by qRT-PCR and western blotting techniques, respectively. Histological sections of hearts were analyzed to evaluate the presence of hypertrophy and fibrosis. Diabetic animals presented hyperglycemia and diastolic dysfunction along with cardiac hypertrophy and fibrosis. XNT treatment prevented further increase in glycemia and improved the cardiac function, as well as the hypertrophy and fibrosis. These effects were associated with increases in cardiac ACE2/ACE ratios (activity: ~26%; mRNA: ~113%; and protein: ~188%) and with a decrease in AT(1) receptor expression. Additionally, XNT inhibited ERK1/2 phosphorylation and prevented changes in AMPK-α and AMPK-ß(1) expressions. XNT treatment did not induce any significant change in AT(2) receptor and Akt expression. These results indicate that activation of intrinsic cardiac ACE2 by oral XNT treatment protects the heart against diabetes-induced dysfunction through mechanisms involving ACE, ACE2, ERK1/2, AMPK-α and AMPK-ß(1) modulations.

The angiotensin-(1-7)/Mas receptor axis is expressed in sinoatrial node cells of rats.

The authors' previous studies have indicated that angiotensin(Ang)-(1-7) protects the heart against reperfusion arrhythmias. The aim of this study was to determine whether a functional angiotensin-converting enzyme2 (ACE2)/Ang-(1-7)/Mas receptor axis is present in the sinoatrial node (SAN) of Wistar rats. SAN cells were identified by Masson's trichrome staining, HCN4 expression, and lack of connexin43 expression. Immunohistochemistry technique was used to detect the expression of ACE2, Ang-(1-7), and Mas in the SAN. To evaluate the role of this axis in the SAN function, atrial tachyarrhythmias (ATs) were induced in isolated rat atria perfused with Krebs-Ringer solution (KRS) alone (control) or KRS containing Ang-(1-7). The specific Mas antagonist, A-779, was used to evaluate the role of Mas in the Ang-(1-7) effects. The findings showed that all components of the ACE2/Ang-(1-7)/Mas branch are present in the SAN of rats. Importantly, it was found that this axis is functional because perfusion of atria with Ang-(1-7) significantly reduced the duration of ATs. Additionally, this anti-arrhythmogenic effect was attenuated by A-779. No significant changes were observed in heart rate, contractile tension, or ±dT/dt. These observations demonstrate that the ACE2/Ang-(1-7)/Mas axis is expressed in SAN cells of rats. They provide the morphological support to the anti-arrhythmogenic effect of Ang-(1-7).