THE INTERACTION BETWEEN ENALAPRILAT AND SELECTED ALPHA-ADRENOCEPTOR ANTAGONISTS IN ISOLATED RAT TAIL ARTERIES

1. Isolated perfused rat tail artery preparations were used to investi gate the effects of the angiotensin converting enzyme inhibitor enalap rilat on the actions of a series of alpha-adrenoceptor antagonists. Th e agonist used was phenylephrine. 2. Enalaprilat (1 mu mol/L) potentia ted the competitive alpha(1)-adrenoceptor antagonist actions of phento lamine (10-100 nmol/L) and yohimbine (0.3-3.0 mu mol/L) as well as the non-competitive antagonist action of phenoxybenzamine (50-100 pmol/L) . 3. The competitive alpha(1)-adrenoceptor antagonist action of prazos in (1-10 nmol/L) was not affected by enalaprilat. 4. For the competiti ve alpha(1)-adrenoceptor antagonists, including prazosin, there appear ed to be an inverse relationship between antagonist potency and the ex tent of potentiation by enalaprilat. 5. The results support the hypoth esis and angiotensin II modulates vascular smooth muscle alpha(1)-adre noceptor function.