Effect of a kinin antagonist on the acute antihypertensive activity of enalaprilat in severe hypertension.

The purpose of this study was to assess the role of kinins in the acute antihypertensive effect of the converting enzyme inhibitor (CEI) enalaprilat in rats with severe hypertension induced by aortic ligation between both renal arteries. For this study, we used a bradykinin analogue, D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-DPhe-Thi-Arg-TFA, with in vivo antagonistic properties. Hypertensive rats were infused intra-aortically for 15 minutes with either saline (30 microliters/min) or the kinin antagonist (40 micrograms/kg/min). Five minutes after the infusion was begun, a bolus injection of enalaprilat (60 micrograms/kg) was given. The blood pressure of the saline-infused animals decreased 48 +/- 6 mm Hg (from 180 +/- 7 to 132 +/- 7 mm Hg), while that of the rats treated with the antagonist decreased only 21 +/- 4 mm Hg (from 175 +/- 3 to 154 +/- 3 mm Hg). The difference between both decrements was significant (p less than 0.01). In another group of hypertensive animals (n = 9), we measured kinin concentration in plasma from arterial blood before and after administration of CEI (41 +/- 10 vs 68 +/- 20 pg/ml, respectively; NS). These results are consistent with the hypothesis that kinins play a role in the acute antihypertensive effect of CEIs in rats with severe hypertension. However, since arterial blood kinin concentrations were not increased significantly after CEI administration, the effect of the CEI may be due to an increase in tissue kinins, which could act as autacoids regulating vascular resistance.