1. The effect of prostaglandin E1 (PGE1) on the pressor and hormonal response to angiotensin (ANG) II has been studied in 22 women in second trimester pregnancy. Three-point dose–response curves were initially determined for all women. Eleven then received an infusion of PGE1 while the remainder received an infusion of normal saline as controls. The dose–response curves to ANG II were re-studied after a period of stabilization.

2. Although assignation to treatment group was random, differences were found in age and basal blood pressure between the control group and those given PGE1. The pressor data from the PGE1 group were thus split by age for analysis.

3. The administration of ANG II alone was associated with significant (P<0.001 at all doses) pressor effects without accompanying bradycardia. Plasma renin concentration (PRC) was suppressed (P<0.001). Plasma aldosterone concentration rose (P<0.001), the magnitude of the rise being directly associated with the plasma ANG II concentrations achieved (P<0.05).

4. The infusion of PGE, had no significant effect on basal blood pressure, but evoked a sustained tachycardia in both age groups (P<0.001). Basal hormone concentrations were unchanged.

5. The pressor response to ANG II was blunted in the presence of PGE1, in both age groups, the overall effect being greatest when the initial response had been large (P<0.05). Measured plasma concentrations of ANG II were lower under these circumstances (P<0.02). PRC fell (P<0.05 for both groups) and plasma aldosterone concentrations rose (P<0.005 for the treated and P<0.001 for the control groups), but the magnitude of these changes did not differ significantly in the two groups.

6. These data support the hypothesis of a for the vasodilator prostaglandins in minimizing the potential pressor effects of the raised ANG II concentrations seen in pregnancy.

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