Coronary vascular actions of the converting enzyme inhibitor, enalapril

Enalapril, a potent angiotensin converting enzyme inhibitor, effectively blocked the constrictor actions of angiotensin I in isolated perfused cat coronary arteries. Enalapril, at concentrations of 25 to 100 micrograms/ml, inhibited angiotensin I by 65 to 80%. Moreover, enalapril at 100 to 200 micrograms/ml, markedly antagonized the coronary vasoconstrictor effects of angiotensin II. At 150 micrograms/ml, enalapril blocked the angiotensin II response by 80 +/- 5%, and at 200 micrograms/ml, it was blocked by 95 +/- 4%. Enalaprilic acid at 0.5 to 1.0 microgram/ml also blocked the angiotensin II response by 94 +/- 5%. Captopril, up to 250 micrograms/ml, failed to significantly antagonize angiotensin II, although it readily blocked angiotensin I in this preparation. The duration of this angiotensin II blockade lasted about 60-90 min. This angiotensin II antagonism may help explain the beneficial effects of enalapril in situations such as acute myocardial ischemia.