Effects of hydralazine on uteroplacental and fetal circulations

Abstract

The effects on uteroplacental and fetal circulations of of hydralazine (Apresoline) when injected either into the mother or into the fetus or the neonate were investigated in near-term normotensive pregnant sheep. Intravenous doses of 0.2–0.5 mg. per kilogram given to the mother decreased arterial pressure and uterine blood flow to an equivalent degree; uterine vascular resistance did not change. Fetal cardiovascular functions were not appreciably affected but fetal blood PO2 decreased significantly. When injected into the fetus, hydralazine reduced fetal arterial pressure only after 10 to 15 times the maternal dose was administered; no alterations occurred either in the fetal ascending aortic, ductus, and main pulmonary artery blood flows or in the fetal blood respiratory gases and pH. Similar effects were observed in the neonate. The implications of these findings in terms of: (a) maternal and fetal vascular reactivity to hydralazine, (b) effects on the fetus of vasodepressor drugs, and (c) the problem of uteroplacental autoregulation are discussed.