Vascular and uterine responses to dobutamine and dopamine in the gravid ewe

Dopamine, a naturally occurring catecholamine precursor of norepinephrine, has been used in the treatment of cardiogenic shock. Following intravenous administration it increases cardiac output, blood pressure, and renal blood flow. Dobutamine is a directly acting inotropic agent which increases myocardial contractility without significantly changing blood pressure. This study was devised to compare the effects of these two drugs on uterine blood flow (UBF), uterine tonus (UT), mean arterial blood pressure (MAP), and heart rate (HR). Chronically instrumented pregnant ewes near term were infused with different concentrations of dopamine and dobutamine while HR, MAP, UT, and UBF were recorded continuously. Dopamine produced a decrease in UBF and an increase in MAP and UT while the HR response was variable. Dobutamine administration resulted in a marked increase in HR and a decrease in UBF, while MAP and UT remained essentially unchanged. Uterine vascular resistance increased with both drugs during high-dosage administration, but the rise was most pronounced following dopamine infusion. Since dobutamine exhibits less α-adrenergic activity than dopamine this drug would seem to be preferred when an inotropic agent is required for treatment of the pregnant patient.