Abstract 628: Renin Does not Participate in the Production of Plasma Ang-(1-12) from Angiotensinogen

Abstract

Angiotensin-(1-12) [Ang-(1-12)] is an extended form of Ang I capable of generating Ang II via angiotensin converting enzyme and chymase. To date no study has addressed the identity of the enzyme or enzymes that accounts for the formation of Ang-(1-12) from the native angiotensinogen (Aogen) substrate. With this in mind, we investigated whether renin is involved in the metabolism of a shorter form of Aogen, [Ang-(1-20)] into the downstream angiotensin peptides. Two groups of male WKY rats (age 12 weeks) received a 15 min intravenous infusion of either saline vehicle (n= 4) or synthetic Ang-(1-20) (n = 5, 20nmol/kg/min) while a third set of rats (n = 5) were administered the Ang-(1-20) 48 h after bilateral Nephrectomy (NTX). Arterial blood was rapidly collected at the end of the infusion period for RIA measurements of angiotensin peptides. Administration of Ang-(1-20) was associated with prompt increases in mean arterial pressure that at 5 min within the infusion period were equivalent in magnitude in both intact (58 ± 2 mm Hg) and anephric (56 ± 3 mm Hg) rats (P > 0.05). Similarly, in intact and anephric rats, Ang-(1-20) metabolism resulted in marked increases in plasma Ang-(1-12) (255-fold and 285-fold higher, respectively; p<0.0001) and Ang II concentrations (82-fold and 97-fold higher, respectively; p<0.0001) compared to the corresponding values in intact vehicle-treated rats. The study demonstrates that renal renin is not involved in the cleavage of Ang-(1-12) from angiotensinogen since the magnitude of the pressor response and Ang-(1-12) and Ang II generation during administration of Ang-(1-20) were not significantly different in intact and anephric rats. Moreover, in a pilot in vitro study, a 15 minutes incubation of plasma from NTX rats with and without aprotinin (kallikrein inhibitor; 20μM) revealed a higher plasma concentration of Ang-(1-12) (2.5-fold) when aprotinin was absent from the inhibitory cocktail. These data further suggest a contributory role of a member of the kallikrein family as the enzyme accounting for the cleavage of Ang-(1-12) from Aogen.