Effects of angiotensin I and angiotensin II on hindlimb and coronary vascular resistance.

BRITTON, STEVEN, AND JOSEPH DI SALVO. Effccfs of ungiotensin I and II on h.indlimb and coronary vascular resistance. ,4m. J. Physiol. 225(5): 1226-1231. 1973.-Effects of angiotensin I (A-I, 0.23.2 pg) and angiotensin II (A-II, 0.1-M pg) on pump-perfusion pressure were examined in the hindlimb vasculature and in the vasculature supplied by the circumflex coronary artery in pentobarbitalizecl dogs& In both vasculatures A-I and A-II caused dose-dependent increases in perfusion pressure reflecting directionally similar changes in resistance to blood flow. Local vasoconstriction produced with A-I in the hindlimb still occurred when none of the injected agonist was permitted to reach the systemic circulation. In both the hindlimb and coronary vasculatures, A-I responses were blocked with SQ 20881 (Pyr-TrpPro-Arg-Pro-Gln-Ile-Pro-Pro), a synthetic nonapeptide that inhibits enzymatic conversion of A-I to A-II. SQ 20881 did not alter responses to A-II in either bed. In contrast I-Sar-8-Alaangiotensin II (P-l 13), a specific A-II antagonist, abolished increases in perfusion pressure produced by A-I or A-II. These results suggest that resistance increases caused by local administration of A-I in the hindlimb or coronary vasculatures are largely ascribable to A-I enzymatic conversion to A-II. Such conversion may occur to the extent of 31 LTb in the hindlimb and 26% in the vasculature supplied by the circumflex coronary artery.