Low-Dose Aspirin Qualitatively Affects the Vascular Response to Angiotensin II in Hypersensitive Pregnant Women

Forty-four women underwent an angiotensin sensitivity test (AST) at 32.4±35 (mean±SD) weeks of gestation. They were divided into two groups according to the effective pressor dose (EPD) and were defined as AST positive (n=17) or AST negative (n=27) if the EPD was <10 or ±10 nanograms/Kg/min, respectively. A regression line of the diastolic blood pressor response to angiotensin II (A II) was obtained for each woman and the mean dose:response curve for each of the two groups was computed. The mean dose:response curves from the AST positive and AST negative groups show no difference between the intercepts (−91±8.2 vs −7.3±6.6, respectively; p NS), but significant difference between the slopes (34.3±8.9 vs 195±72; p<0.00001) and the calculated thresholds (2.6±1.0 vs 4.8±2.4; p<0.001). The administration of 100 mg per day aspirin for 7 days significantly lowered the slope of the mean dose:response curve in the AST positive group with no effect on that of the AST negative group, so resulting in two very similar regression lines. The modulating effect of low-dose aspirin indirectly confirms the role of prostanoids in the abnormal deviations of vascular reactivity in pregnancy and the possible positive effect of the drug when the thromboxane/prostacyclin ratio is unbalanced.