Nitric oxide reverses prostaglandin-induced inhibition in ovarian progesterone secretion in rats

The present studies were undertaken to determine whether nitric oxide (NO) is involved in the regulation of ovarian progesterone and oestradiol secret ion in rats. Immature female Sprague-Dawley rats at 27 days of age were inj ected s.c. with 4 IU pregnant mare's serum gonadotrophin (PMSG) and were ki lled 72 h after the injection, The ovaries were collected, weighed and cult ured in Dulbecco's modified Eagle's medium containing saline, NO donor, NO synthesis inhibitor or prostaglandin F-2 alpha (PGF(2 alpha)). After 24 h c ulture, the medium concentrations of progesterone and oestradiol were measu red by radioimmunoassay. Results showed that: (i) diethylenetriamine (DETA) /NO (1 x 10(-6), 1 x 10(-5), 1 x 10(-4) Mi), an NO donor, caused a dose-dep endent increase in progesterone synthesis (355 +/- 43, 443 +/- 46, 647 +/- 55 ng/g ovary respectively, P < 0.01) with a concomitant decrease in ovaria n oestradiol secretion (408.1 +/- 50.7, 272.9 +/- 28.2, 132.6 +/- 34.6 pg/g ovary respectively, P < 0.01); (ii) neither progesterone nor oestradiol co ncentrations in the culture medium were altered by DETA,without NO; (iii) N -G-nitro-1-arginine methyl ester (1 x 10(-4) M), an inhibitor of NO synthes is, did not significantly affect progesterone and oestradiol secretion by r at ovaries; (iv) PGF(2 alpha) (1 x 10(-6) M) caused a fall in progesterone and oestradiol synthesis; (v) co-incubation with DETA/NO, significantly rev ersed the PGF(2 alpha)-induced decrease in progesterone concentrations from 184 +/- 29 to 388 +/- 60 ng/g (P < 0.01), but not that of oestradiol, It c an be concluded that NO up-regulates progesterone secretion and down-regula tes oestradiol secretion in rat ovaries, and NO can reverse PGF(2 alpha)-in duced inhibition in ovarian progesterone secretion.