Complete blockade of the vasorelaxant effects of angiotensin-(17) and bradykinin in murine microvessels by antagonists of the receptor Mas

The heptapeptide angiotensin-(17) is a biologically active metabolite of angiotensin II, the predominant peptide of the reninangiotensin system. Recently, we have shown that the receptor Mas is associated with angiotensin-(17)-induced signalling and mediates, at least in part, the vasodilatory properties of angiotensin-(17). However, it remained controversial whether an additional receptor could account for angiotensin-(17)-induced vasorelaxation. Here, we used two different angiotensin-(17) antagonists, A779 and d-Pro-angiotensin-(17), to address this question and also to study their influence on the vasodilatation induced by bradykinin. Isolated mesenteric microvessels from both wild-type and Mas-deficient C57Bl/6 mice were precontracted with noradrenaline, and vascular reactivity to angiotensin-(17) and bradykinin was subsequently studied using a small-vessel myograph. Furthermore, mechanisms for Mas effects were investigated in primary human umbilical vein endothelial cells. Both angiotensin-(17) and bradykinin triggered a concentration-dependent vasodilatation in wild-type microvessels, which was absent in the presence of a nitric oxide synthase inhibitor. In these vessels, the pre-incubation with the Mas antagonists A779 or d-Pro-angiotensin-(17) totally abolished the vasodilatory capacity of both angiotensin-(17) and bradykinin, which was nitric oxide mediated. Accordingly, Mas-deficient microvessels lacked the capacity to relax in response to either angiotensin-(17) or bradykinin. Pre-incubation of human umbilical vein endothelial cells with A779 prevented bradykinin-mediated NO generation and NO synthase phosphorylation at serine 1177. The angiotensin-(17) antagonists A779 and d-Pro-angiotensin-(17) equally block Mas, which completely controls the angiotensin-(17)-induced vasodilatation in mesenteric microvessels. Importantly, Mas also appears to be a critical player in NO-mediated vasodilatation induced by reninangiotensin system-independent agonists by altering phosphorylation of NO synthase.