Mesenteric blood flow response to dopamine infusion during myocardial infarction in the awake dog

This study was designed to determine the effects of dopamine on the superior mesenteric arterial circulation of conscious dogs subjected to experimental myocardial infarction. Electromagnetic blood flow transducers were implanted on the superior mesenteric artery in 10 dogs. Direct infusion into the superior mesenteric artery of dopamine (2.5 micrograms/kg/min) after induction of acute myocardial infarction (AMI) revealed a steadily decreasing ability of dopamine to produce mesenteric vasodilation; 4 hr after AMI, infusion of dopamine decreased mesenteric resistance only 14 +/- 0.05%, which was significantly less (P less than 0.001) than during the control period when it decreased resistance 41 +/- 1.0%. Isoproterenol (N = 3) produced substantial increases in flow, despite the reduction in effectiveness of dopamine. Treatment of the 10 dogs with phenoxybenzamine, 5 mg directly into the superior mesenteric artery, restored the ability of dopamine to dilate the mesenteric bed. Beta-adrenergic blockage did not affect the dopaminergic vasodilation after alpha-blockade. The results of this study question the efficacy of dopamine to produce mesenteric vasodilation in the face of increased resistance in the splanchnic circulation during the acute myocardial infarction complicated by hypotension.