Effect of angiotensin converting enzyme inhibitor on regression in cardiac hypertrophy.

Cardiac hypertrophy in rats was produced by aortic banding for 6 weeks and regression of hypertrophy in these experimental animals was induced by administration of angiotensin converting enzyme inhibitor, enalapril (10 mg/kg/day) for 6 weeks. The left ventricular muscle mass and systolic pressure were decrease upon treating the hypertrophied rats with enalapril. This drug also decreased the number of alpha 1-adrenoceptors in hypertrophied myocardium without any changes in beta-adrenoceptors. The regression of cardiac hypertrophy in spontaneously hypertensive rats by enalapril for 10 weeks was not associated with any alterations in alpha 1-adrenoceptors in hypertrophied myocardium, but was decreased in beta-adrenoceptors. Effects of enalapril on extracellular matrix in the myocardium was also observed in regression of hypertrophy in which the type III collagen mRNA expression and collagen contents were reduced in comparison with those of hypertrophied myocardium. These results indicate that regression of cardiac hypertrophy is not always associated with a decrease in the number of alpha 1-adrenergic receptors and that the beneficial effects of enalapril in the hypertrophied heart in aortic banding animals may be of some specific nature.