Response of ovine uterine blood flow to angiotensin II: effect on the fetus.

The effect of intravenous infusion of angiotensin II (2 to 200 ng/kg/min) on uterine blood flow and cardiovascular performance was studied in the normotensive, unanesthetized pregnant ewe. With low rates of infusion (2 to 4 ng/kg/min), only a transient increase in uterine blood flow, lasting 1 to 3 minutes, was observed. Higher rates (110 to 200 ng/kg/min) of infusion caused a decrease in uterine blood flow; this decrease was significantly correlated to the dose. Angiotensin II also caused a significant decrease in the maternal heart rate and an increase in mean maternal arterial blood pressure as the rate of infusion was increased. A high rate of infusion resulted in decreased fetal heart rate and PaO2, probably due to a marked reduction in uteroplacental blood flow.