POTENTIATION OF THE CARDIAC AND PRESSOR RESPONSES TO ELECTRICAL STIMULATION OF THE CARDIAC SYMPATHETIC NERVES BY COCAINE IN OPEN-CHEST DOGS

¹ Department of Pharmacology, The University of Oklahoma School of Medicine, Oklahoma City, Oklahoma

Contractile force, heart rate and arterial blood pressure responses evoked by submaximal and supramaximal stimulation of the postganglionic fibers of the left cardioaccelerator nerves at stimulus frequencies ranging from 5 to 80 cycles/sec were determined before and after intravenous infusion of 5 mg/kg of cocaine in vagotomized open-chest dogs. Comparison of frequency-response curves for contractile force, rate and pressor responses, as well as the duration of the response, showed that cocaine potentiated significantly the positive inotropic, positive chronotropic and pressor responses to endogenous norepinephrine released by both submaximal and supramaximal stimulation at each stimulus frequency employed. Cocaine also significantly prolonged the duration of the cardiac and pressor reponses. The results of this study are consistent with the hypothesis that cocaine potentiates the effects of norepinephrine by preventing the uptake of the amine by tissue binding sites.