Maternal or umblical venous levels of nitrite/nitrate during pregnancy and at delivery.

ABSTRACT

OBJECTIVE: This study was intended to measure serum concentrations of nitrite plus nitrate as an index of nitric oxide synthesis, in the maternal vein during pregnancy, just after a spontaneous delivery and at the puerperium, and at an elective cesarean section, and in the umblical vein and artery. METHODS: Maternal venous sera, and umblical venous and arterial sera were collected, and serum concentrations of nitrite/nitrate were measured by an automated procedure based on the Greiss reaction after reduction of nitrate to nitrite. RESULTS: Compared to a serum concentration of nitrite/nitrate at the first trimester (12-13 weeks of pregnancy), a serum concentration of nitrite/nitrate slightly increased at the second trimester (27-28 weeks), and became maximal at the third trimester (35-36 weeks), followed by a significant decrease near the term (38-40 weeks). A serum concentration of nitrite/nitrate slightly increased just after a spontaneous delivery with labor pains, and at the puerperium to levels slightly more than that at the first trimester. Serum concentrations of nitrite/nitrate in the umblical vein and artery did not differ. They were significantly higher than a serum concentration of nitrite/nitrate in the maternal vein just after a spontaneous delivery with labor pains but not at an elective cesarean section without labor pains. CONCLUSION: A decrease in maternal serum levels of nitrite/nitrate near term may support a hypothesis that NO is one of factors responsible for the maintenance of uterine quiescence during pregnancy. Moreover, the present results suggest that NO plays some role in the feto-placental circulation during a spontaneous delivery.