NITRIC-OXIDE METABOLITES IN NORMAL HUMAN-PREGNANCY AND PREECLAMPSIA

Objective: Alterations in the vascular endothelial release of nitric o xide (NO) may contribute to the vasodilatory adaptation to normal preg nancy and to the vasoconstriction associated with preeclampsia. The ai m of this study was to investigate these hypotheses by measuring plasm a 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: nonp regnant; normal first-, second-, and third-trimester pregnant; and pre eclamptic. Nitrite concentrations in the samples were determined using a colorimetric assay. Nitrate concentrations were determined using an ion-exchange chromatography with UV detection. Results: The plasma nit rite and nitrate concentrations of normal pregnant women (9.45 +/- 0.5 8 mu M, n = 59, and 85 +/- 8 mu M, n = 29, respectively) were not sign ificantly different from those of nonpregnant women (10.04 +/- 1.47 mu M, n = 10, and 95 +/- 15 mu M, n = 9, respectively), and did not chan ge significantly with advancing gestation (ANOVA, P > 0.05). Furthermo re, plasma nitrite and nitrate concentrations were not significantly d ifferent in association with preeclampsia (11.44 +/- 1.73 mu M, n = 14 , and 96 +/- 16 mu M, n = 6, respectively) (ANOVA, P > 0.05). Conclusi ons: These data do not support a role for NO in the vascular changes a ssociated with normal pregnancy and preeclampsia. However, the interpr etation of the results may be confounded by endogenous sources of NO o ther than vascular endothelial cells, the indirect methods available t o human studies for estimating NO production, and dietary sources of n itrite and nitrate.