Effect of captopril on norepinephrine vascular contractility

In isolated aortic rings and in vitro perfused mesenteric arteries of Wistar rats the vasoconstrictor responses to norepinephrine (NE) were not affected by captopril (2 X 10(-4) M). However, captopril (1 mg/kg i.v.) in pithed Wistar rats attenuated significantly the increases in diastolic blood pressure induced by NE. In pithed rats the effect of captopril on NE diastolic blood pressure responses disappeared either in the presence of an angiotensin II (5 ng X kg-1 X min) infusion or when the rats were previously nephrectomized. These findings suggest that the effect of captopril on vascular responses to norepinephrine is mediated by an inhibition of the renin-angiotensin system and not by an antagonistic effect on alpha-adrenergic receptors.