Plasma concentrations of nitrate during the menstrual cycle, ovarian stimulation and ovarian hyperstimulation syndrome

BACKGROUND: Nitric oxide (NO) is predominantly a locally acting mediator, a ffecting several functions in the human female reproductive tract. In vivo, it is quickly metabolized to its stable end product nitrate, which is clea red by the kidney, METHODS AND RESULTS: The aim of the present study was to evaluate possible fluctuations of plasma nitrate concentrations during the menstrual cycle, ovarian stimulation as well as ovarian hyperstimulation s yndrome (OHSS), During the menstrual cycle (n = 19 women) the mean nitrate concentrations were between 26.7 and 29.5 mu mol/l at all stages except for the day of ovulation, when the concentrations were significantly (P < 0.00 1) increased (mean 37.2 mu mol/l +/- 2.0), Significantly lower concentratio ns of plasma nitrate (P < 0.01) were measured at the end of gonadotrophin-r eleasing hormone (GnRH) down-regulation (24.6 mu mol/l +/- 1.4) compared wi th the concentrations found at day 8 of follicle-stimulating hormone (FSH) stimulation (34.9 mu mol/l +/- 2.6) and at the day of human chorionic gonad otrophin (HCG) (35.6 mu mol/l +/- 3.3), The concentrations of nitrate (33.3 mu mol/l +/- 3.4) in women with OHSS (n = 13) were similar to those seen 5 days after embryo transfer (33.2 mu mol/l +/- 2.3), CONCLUSIONS: The resul ts indicate that NO synthesis is increased at the time of spontaneous ovula tion, GnRH treatment inhibits NO synthesis, while NO production is not incr eased in women with OHSS.