Nitric oxide production with preeclampsia

Objective: To clarify production of nitric oxide with preeclampsia. Methods: Production of nitric oxide and elimination of its metabolites, nitrite and nitrate, determines ultimately the level of those metabolites in plasma of subjects whose diets lack them. We measured simultaneously plasma levels and renal clearance of nitrite and nitrate in 20 women with preeclampsia and in 21 healthy pregnant women. Fifteen preeclamptic gravidas were receiving antihypertensive medication and five received betamethasone 1-4 days before the study. Subjects were prescribed low nitrite and nitrate diets for 24 hours and fasted overnight before collection of plasma and urine samples. Nitrite and nitrate were measured spectrophotometrically by Griess reaction. Results: Preeclamptic women had significantly higher plasma levels of nitrite and nitrate (18.1 +/- 6.2 mu mol/L versus 13.0 +/- 4.3 mu mol/L, mean +/- standard deviation [SD], P= .009), which because renal clearance did not differ (0.6 +/- 0.3 versus 0.7 +/- 0.3 mL/s), indicated increased production of nitric oxide with preeclampsia that was unaffected by antihypertensives or betamethasone. The mean plasma level of endothelin-l was increased (5.1 +/- 1.4 versus 3.6 +/- 1.0 pg/mL, P <.001), and urinary output of the prostacyclin metabolite 2,3-dinor-6-keto-prostaglandin F-1 alpha was decreased (39.1 +/- 18.0 versus 61.3 +/- 35.6 ng/mmol creatinine, P = .019) with preeclampsia. These two endothelial markers showed no relation to plasma nitrite and nitrate. Conclusion: Nitric oxide production was increased with preeclampsia. The biologic significance of increased production is unknown, but it might be compensation for the vasoconstriction of preeclampsia. (C) 1999 by The American College of Obstetricians and Gynecologists.