Effects of Isoproterenol on Carbohydrate Metabolism of Isolated Canine Heart

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Abstract
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.