Angiotensin-(1–7) upregulates cardiac nitric oxide synthase in spontaneously hypertensive rats

Abstract

It has been shown that angiotensin (ANG)-(1–7) activates nitric oxide synthase (NOS) in isolated ventricular myocytes from normotensive rats. Since many ANG-(1–7) actions are enhanced in situations of increased ANG II activity, as in hypertension, in this study we investigated the in vivo effect of ANG-(1–7) on NOS activity and expression of endothelial (eNOS), neuronal (nNOS), and inducible NOS (iNOS) in ventricles from spontaneously hypertensive rats (SHR). Rats were subjected to a 60-min ANG-(1–7) infusion (0.35 nmol/min); controls received saline. NOS activity was measured using the NADPH diaphorase histochemical method and by the conversion of l-[14C]arginine to citrulline, and NOS phosphorylation and expression were determined using Western blotting. In SHR, ANG-(1–7) infusion diminished mean arterial pressure from 180 ± 9 to 146 ± 9 mmHg ( P < 0.05), and this effect was prevented by nitro-l-arginine methyl ester (l-NAME), a NOS inhibitor. In addition, NOS activity and eNOS phosphorylation were increased by ANG-(1–7) infusion. Ventricular eNOS and nNOS expression were increased 67.4 ± 6.4 and 51 ± 10%, respectively, by ANG-(1–7), whereas iNOS was not changed. In another set of experiments, we evaluated the mechanism by which ANG-(1–7) modifies NOS activity. Isolated ventricle slices preincubated with ANG-(1–7) showed an increase in NOS activity and eNOS phosphorylation, which was blocked by an AT2 and a bradykinin B2 receptor antagonist, but not by the Mas receptor antagonist. Our results show that in rats in a hypertensive state, ANG-(1–7) infusion upregulates cardiac NOS expression and activity through an AT2- and bradykinin-dependent mechanism. In this way ANG-(1–7) may elicit its cardioprotective action and contribute to some of the counterregulatory AT2 receptor effects that oppose the AT1 receptor-mediated effects.