Cardiac Impairment in Adrenal Insufficiency in the Cat

Cardiac contractile protein ATPase activity was studied in cats 10 days after adrenalectomy at a time when the mean arterial blood pressure was 27% lower than that of control cats. The Ca2+ -dependent, azide-insensitive ATPase activity of myofibrils isolated from the ventricles of adrenalectomized cats was 63% of the activity of control preparations (P <0.025). Similarly, the specific activities of cardiac actomyosin (myosin B) and myosin from adrenalectomized cats had decreased to 54 and 75% of control values, respectively (P <0.005). The percent reductions in ATPase activities in the three protein preparations from adrenalectomized animals were not significantly different, suggesting that the depression was associated with myosin per se. The reduction in the myosin ATPase activity in adrenal insufficiency was prevented by dexamethasone treatment adequate to prevent the decline in mean arterial blood pressure of the adrenalectomized cats. The reduction in cardiac performance in frank adrenal insufficiency may reflect a decrease in the rate of conversion of chemical to mechanical energy by the myocardial contractile proteins.