Comparison of angiotensin converting enzyme inhibitors captopril and MK421-diacid in guinea pig atria

Abstract

Angiotensin I (AI) and angiotensin II (AII) caused concentration-dependent increases in atrial rate in guinea pig isolated right atria. Converting enzyme inhibitors captopril and MK421-diacid did not alter the responses to AII but displaced the curves to AI to the right. The atrial response to generated AII from AI was used as a bioassay to estimate the dissociation constants of converting enzyme inhibitors (KB) and test for kinetics of simple competition. MK421-diacid was 12-40 times more potent than captopril. However, estimations of KB for captopril and MK421-diacid were unsatisfactory because at high concentration of inhibitors the curves to AI were not displaced according to simple comp..