SUMMARY Conscious pregnant and nonpregnant rabbits were used to further evaluate the role of prostaglandin (PG) and plasma renin activity (PRA) in the systemic hemodynamics of pregnancy. Pregnant rabbits had high peripheral blood levels of both PGE 2 and PRA. Systemic blood pressure was not affected in either pregnant or nonpregnant by the administration of an inhibitor of prostaglandin synthesis. Pregnant rabbits, however, had a much larger decrease in blood pressure than nonpregnant animals when given the angiotensin I (Al)-converting-enzyme inhibitor, captopril. Pregnant rabbits were more resistant to the pressor effect of exogenous All than nonpregnant animals. The pressor effect of All increased in pregnant rabbits after the administration of meclofenamate and parturition but was not changed by volume expansion. In contrast, the sensitivity of nonpregnant rabbits to AH increased after volume expansion, but not after treatment with inhibitors of prostaglandin synthesis. These studies demonstrate that a remarkable similarity exists between pregnant rabbits and pregnant women in the pressor response to AH. This study is the first to correlate the vasopressor response to AH with PRA and the level of a circulating vasopressor prostaglandin in pregnant animals. The results strongly suggest that this model will be fruitful in further attempts to define the factors controlling systemic hemodynamics during pregnancy. (Hypertension 5: S14- S2O, 1983)

The relationship between norepinephrine (NE) and prostaglandins in the regulation of systemic blood pressure during pregnancy was examined in conscious rabbits. The arterial prostaglandin E2 (PGE2) concentration was higher in pregnant than in nonpregnant rabbits. Resting blood pressure was slightly lower in the gravid animals. The pressor response to incremental doses of intravenous NE was blunted in the pregnant rabbits. Meclofenamate, a cyclooxygenase inhibitor, failed to alter the resting blood pressure in either group of animals, although it reduced PGE2 levels more than 60% in the pregnant rabbits. The pressor response to NE was significantly increased only in the pregnant rabbits when the NE infusion was repeated following meclofenamate. Pregnant rabbits could also be differentiated from nonpregnant by their higher peripheral blood levels of NE and their uniform hypotensive response to alpha-adrenergic blockade. These observations define an altered responsiveness to both endogenous and exogenous NE in pregnant rabbits that appears to be related to an increase in vasodilator prostaglandins.