Effects of isoproterenol on carbohydrate metabolism of isolated canine heart.

• Early studies of the effects of epinephrine on the isolated and metabolically supported canine heart demonstrated increases in heart rate, contractile force, and myocardial oxygen consumption. The increases in myocardial oxygen consumption following epinephrine administration were roughly proportional to the increase in heart rate. In heart-lung preparations epinephrine administration resulted in increased myoeardial glucose utilization. This increase was somewhat dependent on arterial glucose concentration and was associated with a myocardial glycogen depletion unless glucose was administered witli the epinephrine. In the isolated heart, stimulated by either epinephrine or pressure work loads, both lactate and glucose utilization were increased, but epinephrine stimulation did not effect pyruvate utilization. Increased Avork loads applied to heart-lung preparations resulted in no change in myoeardial glycogen content Avhen arterial glucose concentrations were maintained." Under these conditions only 25% to 60% of the oxidative metabolism can be accounted for by carbohydrate utilization. Stimulation of the stellate ganglion increased heart rate, blood pressure, and coronary blood flow, but did not effect myocardial utilization of lactate. Isoproterenol, or isopropyl norepinephrine, described in 1.941, has marked excitatory and