Effect of prostaglandin synthetase inhibitors on pressor response to angiotensin ii in human pregnancy

Pregnant women destined to develop pregnancy-induced hypertension (PIH) lose refractoriness to the pressor effects of infused angiotensin II (AII) several weeks before the onset of hypertension. This loss of refractoriness to A-II is unrelated to plasma renin activity or circulating levels of A-II. In animal studies it has been shown that the prostaglandins are important mediators of vascular reactivity. Specifically, the uterine blood flow appears to vary directly with prostaglandin E concentrations in uterine venous effluent. The present study was designed to evaluate the effects of prostaglandin synthetase inhibitors on the pressor effects of A-II in human pregnancy. The "effective A-II pressor dose" (nanograms of A-II kg^-1 min^-1 necessary to cause a 20 mm Hg rise in diastolic pressure) was determined in 14 pregnant women before and after treatment with either 25 mg indomethacin or 600 mg aspirin given twice, 6 h apart. The effective pressor dose required before treatment [22.7 ± 3.4 ng kg^-1min^-1 (mean ± SE)] was significantly greater than that after treatment [8.7 ± 1.2 ng kg^-1min^-1 (P < 0.001)]. The refractoriness to A-II observed in normal human pregnancy may be mediated in part by the action of prostaglandins or related substances produced in the arteriole.