Systemic and uterine hemodynamic responses to dopamine in pregnant and nonpregnant sheep.

The systemic and uterine hemodynamic effects of dopamine were studied in nonpregnant and near-term pregnant, unanesthetized, chronically instrumented sheep. Dopamine was administered by constant intravenous infusion in doses ranging from 2 to 40 microgram per kilogram per minute. A hypertensive effect was consistently observed when doses greater than 5 microgram per kilogram per minute were given. The rise in pressure was accompanied by a rise in the systemic vascular resistance and an increase in the cardiac output; the increment in the latter was greater in the pregnant than in the nonpregnant animals. Uterine blood flow increased consistently despite some rise in uterine vascular resistance; uterine fraction of cardiac output either remained unchanged or increased slightly. Venomotor construction, reflected by a rise in central venous pressure, occurred at all dose levels. These hemodynamic properties of dopamine may be explained partly on the basis of its combined beta- and alpha-mimetic action, as well as through redistributions of flows and resistances among various regional vascular beds.