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

BACKGROUND: Nitric oxide (NO) is predominantly a locally acting mediator, affecting several functions in the human female reproductive tract. In vivo, it is quickly metabolized to its stable end product nitrate, which is cleared 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 syndrome (OHSS). During the menstrual cycle (n = 19 women) the mean nitrate concentrations were between 26.7 and 29.5 μmol/l at all stages except for the day of ovulation, when the concentrations were significantly (P < 0.001) increased (mean 37.2 μmol/l ± 2.0). Significantly lower concentrations of plasma nitrate (P < 0.01) were measured at the end of gonadotrophin-releasing hormone (GnRH) down-regulation (24.6 μmol/l ± 1.4) compared with the concentrations found at day 8 of follicle-stimulating hormone (FSH) stimulation (34.9 μmol/l ± 2.6) and at the day of human chorionic gonadotrophin (HCG) (35.6 μmol/l ± 3.3). The concentrations of nitrate (33.4 μmol/l ± 3.4) in women with OHSS (n = 13) were similar to those seen 5 days after embryo transfer (33.2 μmol/l ± 2.3). CONCLUSIONS: The results indicate that NO synthesis is increased at the time of spontaneous ovulation. GnRH treatment inhibits NO synthesis, while NO production is not increased in women with OHSS.