Abstract

The myocardial metabolic effects of the beta adrenergic blocking drug, dl-propranolol, were studied in 19 open-chest anesthetized mongrel dogs in which arterial and left intraventricular pressures, heart rate, coronary blood flow and velocity of left ventricular pressure development (dp/dt) were measured. Myocardial uptake of glucose, lactate, pyruvate and free fatty acids (FFA) was determined during a control period and 10 min after the administration of propranolol (1 mg/kg). A significant decrease in the uptake of FFA (48.3%) occurred during beta receptor blockade, whereas glucose, lactate and pyruvate uptake did not change from control. To determine whether the decline in uptake of FFA after propranolol was due to a reduction in myocardial energy requirements or to a specific metabolic blockade, heart rate was elevated with pacing electrodes on the left atrium by approximately 50 beats/min. In control dogs, atrial tachycardia caused a marked increase in FFA uptake with no significant change in the uptake of carbohydrates. In propranololtreated dogs, atrial tachycardia increased the uptake of glucose (54.1%) and lactate (13.9%), whereas FFA uptake decreased by 19.4%. These results demonstrate that propranolol interferes specifically with the myocardial uptake of FFA.