Effects of Isoproterenol on Carbohydrate Metabolism of Isolated Canine Heart

Chronotropic and inotropic effects of intraarterial infusion of isoproterenol were monitored in the isolated, metabolically supported preparations of the canine heart.The time-dosage relationship was found to be hyperbolic over a narrow range of concentration of isoproterenol. Increasing concentration beyond the optimal range by a factor of about two produced arrhythmias and A-V conduction defects.Oxidative metabolism increased significantly and proportionally to heart rate.Since utilization of glucose remained the same, pyruvate utilization increased slightly and lactate was excreted; the augmented oxidative metabolism could not be accounted for by the observed changes in carbohydrate substrates.Myocardial glycogen concentrations were insignificantly changed during this inotropic stimulation.