Contrasting effects of dopamine and dobutamine on myocardial release of norepinephrine during acute myocardial infarction.

The effects of dopamine and dobutamine on release of norepinephrine from normal and ischemic myocardium were compared in 2 groups of open-chest anesthetized dogs. Both agents were infused intravenously at a rate of 10 micrograms/Kg/min for 2 hours, beginning 40 min after snare occlusion of the left anterior descending coronary artery. There were no major differences in hemodynamic responses between the 2 groups. Blood samples were taken simultaneously from the aorta, coronary sinus and the cardiac vein that ran parallel to the left anterior descending coronary artery before and after coronary artery occlusion. Plasma norepinephrine increased 40 min after the occlusion, with a net efflux in both coronary sinus and cardiac venous blood. Dopamine caused further increases in plasma norepinephrine. At 20 min after the beginning of dopamine infusion the coronary sinus concentration (4.09 +/- 1.36 ng/ml) was significantly greater than the arterial concentration (2.84 +/- 0.87 ng/ml). This transcardiac difference disappeared during continuous infusion 2 hours after coronary artery occlusion. Differences in norepinephrine concentration between the arterial and cardiac venous blood, however, were not significant. In contrast, plasma norepinephrine did not increase during dobutamine infusion in either the ischemic or non-ischemic bed. Thus, the results suggest that while these two agents have similar systemic hemodynamic effects, only dopamine increases myocardial release of norepinephrine from either ischemic or normal myocardium during acute myocardial infarction.