Catecholamine-Mediated Reduction in Uteroplacemental Blood Flow in the Diet-Restricted, Term-Pregnant Rat

Abstract

To determine whether the reduction in maternal placental blood flow associated with malnutrition during pregnancy results from α-adrenergic vasoconstriction, we measured cardiac output, uteroplacental blood flow and uteroplacental vascular resistance in ad libitum-fed and in 50% diet-restricted term-pregnant rats, using radioactive-labeled microspheres before, and again after, α-adrenergic receptor blockade with phenoxybenzamine. Uteroplacental blood flow in the diet-restricted rats was 40% lower than that of the ad libitum-fed rats, before phenoxybenzamine. Phenoxybenzamine caused a 50% reduction in mean blood pressure in both the ad libitum-fed and diet-restricted rats, but did not alter cardiac output. Phenoxybenzamine decreased preplacental vascular resistance in the diet-restricted rats, resulting in no significant reduction of placental blood flow. In the ad libitum-fed rats, on the other hand, phenoxybenzamine did not alter preplacental vascular resistance, and placental blood flow decreased 45% with the fall in blood pressure. Myometrial vascular resistance was unaffected by phenoxybenzamine in either group, and myometrial blood flow decreased with the fall in blood pressure in both groups. Thus, the decreased uteroplacental blood flow associated with diet restriction is the result of increased uteroplacental α-adrenergic vasomotor tone.