COCAINE POTENTIATION OF THE CARDIAC INOTROPIC AND PHOSPHORYLASE RESPONSES TO CATECHOLAMINES AS RELATED TO THE UPTAKE OF H³-CATECHOLAMINES

¹ Department of Pharmacology, Division of Basic Health Sciences, Emory University, Atlanta, Georgia

The effects of cocaine on the contractile force and phosphorylase responses to catecholamines and on the myocardial uptake of these agents has been studied in the dog heart in situ. The effects of norepinephrine on the heart were potentiated by cocaine to a greater extent than were those of epinephrine, while those of isoproterenol were not potentiated at all. Cocaine decreased the amount of H³-norepinephrine and H³-epinephnne found in the heart at the peak of the contractile force response less than 30 seconds after their injection, but had no effect on the amount of H³-isoproterenol in the heart. It was shown by the concurrent administration of K⁴² that the changes induced by cocaine in myocardial uptake of catecholamines were not due to alterations in blood flow to the heart. The results support the concept that the ability of cocaine to potentiate the actions of a catecholamine in a tissue depends on the extent to which the amine is inactivated in that tissue by an uptake mechanism which is sensitive to inhibition by cocaine.