CORONARY VASODILATATION PRODUCED BY DOPAMINE AFTER ADRENERGIC BLOCKADE

¹ Cardiovascular Division, Department of Internal Medicine, University of Iowa ColLege of Medicine and the Veterans Adminitration Hospital, Iowa City, Iowa

Dopamine causes renal and mesenteric vasodilatation. This vasodilatation is not reduced by alpha or beta receptor antagonista, but is attenuated by haloperidol. The effects of dopamine on the left circumflex coronary artery of anesthetized dogs were studied to determine if the dilatation occurred in the coronary circulation. The left circumflex coronary artery was perfused at constant flow with heparin-treated blood from a femoral artery. Perfusion pressure, left ventricular pressue and dp/dt, systemic arterial preesure and heart rate were monitored continuously. With flow constant, changes in perfusion pressure reflected changes in coronary resistance. Drugs were administered into the perfusion tubing 1) before adrenergic blocakade, 2) after beta receptor blockade and 3) after combined beta and alpha receptor blockade. Before blockade, dopamine, isoproterenol and nitroglycerin decreased perfusion pressure. Dopamine and isoproterenol usually increased heart rate and dp/dt. Administration of propranolol abolished the dilatation with isoproterenol and reversed the response to dopamine from dilatation to constriction. After both beta and alpha receptor blockade, there was again no response with isoproterenol, but dopamine caused vasodilatation. This vasodilatation occurred in the absence of changes in heart rate, pressures and dp/dt. It was not altered by tripelennamine or atropine, but was reduced by haloperidol. These experiments indicate that dopamine, in addition to effects on beta and alpha receptors, produces a dilator action in the coronary circulation which resembles that seen in the kidney and mesentery.