The dopamine-induced coronary vasoconstrictor response is potentiated by adenosine administration in the dog heart

The ineffectiveness of beta-adrenergic blockade in abolishing adenosine-induced coronary vasodilation was utilized to demonstrate that dopamine (DA) is capable of eliciting very strong coronary vasoconstrictor actions in vivo. In 2 separate groups of dogs anesthetized with pentobarbital, responses to DA were assessed either by flowmeter recordings or by computer-aided infrared thermography, which senses coronary blood flow-dependent heat emission from the epicardium. In untreated controls, submaximal DA infusions (16 micrograms.kg-1.min-1 iv) elicited a coronary vasodilator response. The thermographic equivalent of this hemodynamic action was an increased epicardial temperature. Pretreatment with oxprenolol (0.5 mg.kg-1 iv) preserved both basic heart activity and cardiac heat emission at levels which were comparable to the control state, but prevented DA mediated excitation of cardiac and coronary beta-adrenoceptors. In this state, DA infusion constricted the coronary arteries and tended to decrease heart emission. However, both types of effects were moderate, and only the hemodynamic effect was statistically significant. If DA was given after the coronary bed had been dilated submaximally by adenosine (30 micrograms.kg-1.min-1 infused into the left heart), the flow-reducing effect of DA became a dramatic phenomenon, and the DA-induced epicardial cooling was significantly potentiated. The results show that after eliminating conventional beta-effects, DA affects the coronary arteries through vasoconstrictor mechanisms. This finding suggests that the DA-induced constriction is limited in undilated coronary arteries by the metabolic autoregulatory capacity of the vessels.