Comparison of dobutamine and dopamine in acute myocardial infarction. Effects of systemic hemodynamics, plasma catecholamines, blood flows and infarct size.

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Abstract
To compare cardiovascular effects of dobutamine and dopamine, the 2 agents were administered at a dose of 10 .mu.g/kg per min i.v. to 2 groups of chronically instrumented conscious dogs, beginning 40 min after coronary occlusion and continuing for 24 h thereafter. A control group that was given an infusion of 5% dextrose was also studied. During the first 30 min of infusion, both dobutamine and dopamine produced similar increases in cardiac output, left ventricular dP[pressure]/dt and dP/dt/P, without significant changes in heart rate, mean arterial blood pressure or regional myocardial blood flow. At 24 h, cardiac output and left ventricular dP/dt and dP/dt/P continued to be greater in the dobutamine group than in the control group. The acute positive inotropic effects of dopamine were no longer apparent at 24 h. Epicardial blood flow in the dobutamine-treated group was higher than that in the control group. There were no differences between groups in the ischemic-to-nonischemic myocardial blood flow ratio. Infarct size, measured by nitroblue tetrazolium staining, was smaller in the dobutamine group (55 .+-. 4% of risk zone) than in the dopamine group (76 .+-. 6%) or the control group (76 .+-. 5%). The dobutamine group differed from the dopamine group in their plasma catecholamine levels. Arterial plasma concentrations of norepinephrine and epinephrine increased above the postocclusion baseline values only during dopamine infusion by 1.50 .+-. 0.34 and 0.87 .+-. 0.32 ng/ml, respectively. Dopamine caused myocardial release of norepinephrine, as evidenced by a significant transmyocardial gradient (coronary sinus minus arterial difference) of 1.48 .+-. 0.27 ng/ml. Dobutamine evidently increases collateral flow to the ischemic myocardium, enhances left ventricular performance and reduces infarct size. None of these effects were produced by dopamine under these experimental conditions. The difference between the effects of the 2 drugs probably is related, at least in part, to the detrimental effects of local myocardial release of norepinephrine by dopamine.