Role of endogenous bradykinins in the acute depressor effect of angiotensin converting enzyme inhibitor captopril--assessed by a competitive antagonist of bradykinin.

To examine whether a hypotensive effect of converting enzyme inhibitor captopril was mediated partly by a potentiation of endogenous bradykinin, a newly synthesized competitive antagonist of bradykinin (B 4147) was used in anesthetized rats. The injection of B 4147 alone (50 and 100 micrograms) elicited significant increases in blood pressure. Although the administration of captopril (1 mg/kg, i.v.) caused a decrease in mean arterial pressure (MAP), the injection of the kinin antagonist (50 and 100 micrograms) after the captopril produced an increase in MAP by an average of 42 and 47% of the initial fall induced by captopril, respectively. The hypertensive effect of B 4147 was enhanced in magnitude and duration after the captopril. These results suggest that an accumulation of endogenous kinins by captopril contributes partly to the acute hypotensive effect of converting enzyme inhibitors in anesthetized rats.