Maternal and uteroplacental hemodynamic effects of chronic captopril in the hypertensive, term-pregnant rat. The chronic effects of captopril on maternal hemodynamics and organ perfusion were investigated in 10 untreated and 10 captopril-treated pregnant spontaneously hypertensive rats by means of the radioactive-labeled microsphere technique. The normal decrease in blood pressure during gestation was prevented by reduction of litter size to two conceptuses on day 7 of gestation. Captopril (approximately 10 mg/kg/day) or drug vehicle (50% ethyl alcohol) was administered intraperitoneally by an osmotic pump from day 7 to 21. At term mean arterial pressure was 23% lower in the captopril-treated group as the result of a 29% decrease in total peripheral resistance without a significant change in cardiac output. The decrease in total peripheral resistance was primarily caused by a decline in splanchnic and skin resistances. Maternal organ and uteroplacental perfusion were not significantly altered. We conclude that administration of captopril during the last 2 weeks of pregnancy in the hypertensive rat effectively lowers maternal blood pressure without adverse effects on organ and uteroplacental perfusion. 