CARDIAX ADRENERGIC ACTIVITY IN EXPERIMENTAL HEART FAILURE ASSESSED WITH BETA RECEPTOR BLOCKADE

The role of cardiac adrenergic activity in supporting the performance of the heart in calves with chronic pulmonary arterial hypertension was assessed by beta adrenergic blockade acutely induced with the intravenous administration of propranolol. Studies were performed in animals with chronic ventricular failure. There was a minimal hemodynamic response to propranolol in animals before failure. However, in those animals with clinical and hemodynamic evidence of failure, further marked deterioration of ventricular performance occurred, with a fall in cardiac output and an increase of right ventricular end-diastolic pressure. These changes were more pronounced in the animals that had had a longer period of failure. A consistent reduction in the norepinephrine content of the heart was demonstrated only in those animals with failure, and the reduction was greater in animals in which failure had been present for a longer period. Plasma catecholamine levels tended to be elevated in those animals with failure that had marked depletion of cardiac norepinephrine, and these values were increased further after administration of propranolol. The striking deterioration in ventricular performance observed with propranolol in the norepinephrine-depleted failing heart suggests that adrenergic support is necessary in maintaining the ventricular function of these hearts but that this support is now derived primarily from circulating catecholamines arising from adrenal medullary secretion. © 1969.