EFFECT OF NOREPINEPHRINE ON MYOCARDIAL METABOLISM BEFORE AND AFTER BETA RECEPTOR BLOCKADE

Cardiac beta-adrenergic receptors were stimulated by the infusion of 0.02 μg/min/kg of norepinephrine (NE) into the left circumflex coronary artery in 20 anesthetized, bilaterally vagotomized open chest dogs. NE increased myocardial extraction ratio and uptake of glucose, lactate and plasma unesterified fatty acids (FFA). The increase in metabolism was accompanied by a slight rise in peak intraventricular pressure and a significant increase in dp/dt. Mean blood pressure, coronary artery perfusion pressure, coronary flow and coronary vascular resistance were not altered. In 10 of 20 dogs treated with the beta-adrenergic receptor blocking drug, dl-propranolol, the intracoronary infusion of NE caused moderate decreases in the uptake of lactate and pyruvate, while that of glucose was not significantly altered. FFA uptake was markedly decreased from 12.7 ± 3.3 to 1.0 ± 2.3 μEq/min/100 g while the extraction ratio declined 58% from control. Myocardial glycogen concentration in 8 control dogs was found to be not significantly different from cardiac glycogen levels in dogs infused with NE before and after beta-receptor blockade. These data indicated that the myocardial uptake of FFA in dogs pretreated with propranolol was not stimulated by subsequent administration of NE, suggesting that FFA utilization by the normal heart is closely associated with the cardiac beta-adrenergic receptor.{A table is presented}. © 1969.