Nitric Oxide Metabolites in Normal Human Pregnancy and Preeclampsia

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Abstract
Objective: Alterations in the vascular endothelial release of nitric oxide (NO) may contribute to the vasodilatory adaptation to normal pregnancy and to the vasoconstriction associated with preeclampsia. The aim of this study was to investigate these hypotheses by measuring plasma levels of the stable metabolites of NO, nitrite and nitrate, during normal human pregnancy and those complicated by preeclampsia. Methods: Plasma samples were obtained from women in the following groups: nonpregnant; normal first-, second-, and third-trimester pregnant; and preeclamptic. Nitrite concentrations in the samples were determined using a colorimetric assay. Nitrate concentrations were determined using anion-exchange chromatography with UV detection. Results: The plasma nitrite and nitrate concentrations of normal pregnant women (9.45 ± 0.58 u.M. n = 59. and 85 ± 8 µM, n = 29, respectively) were not significantly different from those of nonpregnant women (10.04 ± 1.47 µM, n = 10, and 95 ± 15 µM, n = 9, respectively), and did not change significantly with advancing gestation (ANOVA, P ± 0.05). Furthermore, plasma nitrite and nitrate concentrations were not significantly different in association with preeclampsia (11.44 ± 1.73 µM, n = 14, and 96 ± 16 µM, n = 6, respectively) (ANOVA, P ± 0.05). Conclusions: These data do not support a role for NO in the vascular changes associated with normal pregnancy and preeclampsia. However, the interpretation of the results may be confounded by endogenous sources of NO other than vascular endothelial cells, the indirect methods available to human studies for estimating NO production, and dietary sources of nitrite and nitrate.

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