Metabolic, hormonal, and hemodynamic changes during dopamine infusions in halothane anesthetized horses.

Selected metabolites, hormones and cardiovascular variables were measured in halothane anesthetized horses during 1 hour of dopamine infusion at a rate of 5 micrograms/kg/min (low) and 10 micrograms/kg/min (high), and for 1 hour after infusion. Plasma cortisol increased twofold in the low-infusion group but did not change significantly in the high-infusion group. Plasma nonesterified fatty acids, blood glucose, blood lactate, and plasma insulin increased in the high-infusion group. There was little difference in heart rate, systolic, diastolic, and mean arterial blood pressure between the two groups. The high infusion was associated with arrhythmias in several horses, and one horse showed ventricular fibrillation and died. If metabolic and hormonal changes are used as markers of a "stress response" in anesthetized horses the results must be carefully interpreted if a sympathomimetic agent such as dopamine is administered to maintain cardiovascular stability.