CHARACTERIZATION OF A NEW ANGIOTENSIN ANTAGONIST SELECTIVE FOR ANGIOTENSIN-(1-7) - EVIDENCE THAT THE ACTIONS OF ANGIOTENSIN-(1-7) ARE MEDIATED BY SPECIFIC ANGIOTENSIN RECEPTORS

In this study we describe a new angiotensin antagonist [Asp(1)-Arg(2)-Val-(3)Tyr(4)-Ile(5)-His(6)-D-Ala(7), (A-779)] selective for the heptapeptide angiotensin-(1-7) [Ang-(1-7)]. A-779 blocked the antidiuretic effect of Ang-(1-7) in water-loaded rats and the changes in blood pressure produced by Ang-(1-7) microinjection into the dorsal-medial and ventrolateral medulla. In contrast, A-779 did not change the dipsogenic, pressor, or myotropic effects of angiotensin II (Ang II). Also, A-779 did not affect the antidiuretic effect of vasopressin or the contractile effects of angiotensin III, bradykinin, or substance P on the rat ileum. In the rostral ventrolateral medulla, the pressor effect produced by Ang-(1-7) microinjection was completely blocked by A-779 but not by AT, or AT, receptor antagonists (DUP 753 and CGP 42112A, respectively). Conversely, the presser effect produced by Ang II was not changed by A-779 but was completely blocked by DUP 753. Binding studies substantiated these observations: A-779 did not compete significantly for I-125-Ang II binding to adrenocortical membranes at up to a 1 mu M concentration. Low affinity binding was also observed in adrenomedullary membranes with an IC50 greater than 10 mu M. Our results show that A-779 is a potent and selective antagonist for Ang-(1-7). More importantly, our data indicate that specific angiotensin receptors mediate the central and peripheral actions of Ang-(1-7).