Hypophyseal Influence on Function and Composition of Cardiac Muscle

Abstract

The effects of hypophysectomy and of growth hormone (GH) on the properties and composition of rat myocardium were studied. GH, in dosage sufficient to maintain a normal rate of growth, did not correct the microcardia of hypophysectomy. Tension production of surviving left ventricular muscle columns was not modified by hypophysectomy or GH administration. Ventricular actomyosin concentration was slightly but significantly elevated in hypophysectomized animals, with or without GH. However, "ATP sensitivity" of the extracted actomyosin was markedly depressed by hypophysectomy and partially restored by GH. Differential hormonal regulation of cardiac actin and myosin is suggested.