The antihypertensive contribution of bradykinin as assessed by a specific bradykinin antagonist.

A new specific antagonist of bradykinin was used to examine the contribution of bradykinin to the depressor effect of different antihypertensive drugs in two-kidney renovascular rats. First we tested the inhibitory capacity of this peptide for exogenously injected bradykinin (75-200 ng). An inhibition of the vasodepressor action of bradykinin by over 50% was found when the bradykinin inhibitor was infused at a rate of 40 micrograms/min, with little difference at higher rates of infusion. We then infused this inhibitor in four groups of renovascular hypertensive rats. In three groups the blood pressure had been decreased by pretreatment either with the converting enzyme inhibitor MK 421, saralasin or sodium nitroprusside, respectively. The fourth group received no pretreatment. Infusion of the inhibitor produced an immediate increase in blood pressure by 30% only in the MK 421 group, but no change in the three other groups. These results indicate that bradykinin is involved in the decrease of blood pressure produced by converting enzyme inhibition in experimental renovascular hypertension.