The interaction between enalaprilat and selected alpha-adrenoceptor antagonists in isolated rat tail arteries.

1. Isolated perfused rat tail artery preparations were used to investigate the effects of the angiotensin converting enzyme inhibitor enalaprilat on the actions of a series of alpha-adrenoceptor antagonists. The agonist used was phenylephrine. 2. Enalaprilat (1 mumol/L) potentiated the competitive alpha 1-adrenoceptor antagonist actions of phentolamine (10-100 nmol/L) and yohimbine (0.3-3.0 mumol/L) as well as the non-competitive antagonist action of phenoxybenzamine (50-100 pmol/L). 3. The competitive alpha 1-adrenoceptor antagonist action of prazosin (1-10 nmol/L) was not affected by enalaprilat. 4. For the competitive alpha 1-adrenoceptor antagonists, including prazosin, there appeared to be an inverse relationship between antagonist potency and the extent of potentiation by enalaprilat. 5. The results support the hypothesis and angiotensin II modulates vascular smooth muscle alpha 1-adrenoceptor function.