The influence of E2 and P4 on in vitro NOx production in the porcine myometrium during first half of pregnancy.

The aim of the present study was to determine 1) concentrations of NOx in the myometrium of pregnant gilts, and 2) the influence of estradiol-17beta (E2) and/or progesterone (P4) on NOx production by the porcine myometrium on days 5, 10, 15, 20, 25, 30, 35, 40 and 60 of pregnancy (n = 5 per day). Total NOx concentrations were determined using a microplate assay method based on the Griess reaction. During the first 60 days of gestation, a triphasic pattern in the concentration of NOx in the porcine myometrium was observed with a peak on days 10-15, 30 and 60 of gestation. We also demonstrated the stimulatory effect of E2 and/or P4 on in vitro NO production by the porcine myometrium. The stimulatory effect of steroid hormones on NOx release depended on the treatment dose of steroids and day of pregnancy. These data suggest that locally produced NO may inhibit spontaneous uterine contraction and therefore is involved in the maintenance of myometrial quiescence during pregnancy.