Effects on the renin-angiotensin system of the administration of prostaglandin E1 and E2 in second trimester human pregnancy.

We have measured evoked changes in plasma renin concentration (PRC), plasma renin substrate (PRS) amd plasma aldosterone concentration (ALD) during the infusion of angiotensin II (AII) with and without the simultaneous administration of prostaglandin E2, 5 micrograms min-1 i.v. (PGE2) or prostaglandin E1, 15 ng kg-1 min-1 (PGE1). Experiments have been carried out using PGE2 in 20 patients, and in 5 patients to date with PGE1. AII alone (16 ng kg-1 min-1 i.v.) significantly reduced PRC in both groups of patients without altering PRS, while ALD concentrations more than doubled. The infusion of PGE2 stimulated basal PRC; PGE1 at the dose used did not alter PRC. Neither prostaglandin altered basal RS or ALD concentrations. When AII was infused simultaneously, PRC was again suppressed, in the presence of PGE2. However, only minimal feedback suppression occurred when PGE1 was being used. Furthermore, AII was still associated with a more than two-fold rise in ALD concentration when given together with PGE2, but the rise was considerably smaller and not significant in the presence of PGE1. PGE2 is a known stimulus to renin secretion, apparently acting directly at the juxtaglomerular apparatus. These preliminary results suggest that while a similar mechanism exists in second trimester human pregnancy, PGE1 may have a different effect. The apparent blockade of the normal feedback suppression of PRC in the presence of increased PGE1 concentrations by raised concentrations of AII is especially interesting.