INDOMETHACIN INHIBITS THE SECRETION OF INHIBIN AND ESTRADIOL-17-BETA STIMULATED BY PREGNANT MARE SERUM GONADOTROPIN IN THE IMMATURE FEMALE RAT

The involvement of prostaglandins (PGs) in the regulation of inhibin and oestradiol-17beta secretion from the ovary was studied by determining the effects of indomethacin and/or pregnant mare serum gonadotrophin (PMSG) on the levels of ovarian hormones in immature female rats. An increase in serum and ovarian levels of inhibin and oestradiol-17beta was observed with a reciprocal reduction in serum follicle-stimulating hormone (FSH) levels from within 26 to 50 h after a single injection of 5 IU PMSG (s.c.) when the rats were 26 days of age. Administration of indomethacin to suppress PGs synthesis, simultaneously with PMSG, resulted in a substantial reduction in the levels of ovarian PGF2alpha and serum inhibin and oestradiol-17beta, which were both enhanced by PMSG treatment, 24 h after treatment with drugs. Indomethacin also reduced the basal serum level of inhibin. In the indomethacin-treated animals, the serum level of FSH was significantly increased regardless of the treatment with PMSG, indicating that the negative feedback regulation between FSH and inhibin is operating in these animals. These results demonstrate the inhibitory effects of indomethacin on PMSG-enhanced inhibin and oestradiol-17beta production, suggesting that PGs play a regulatory role in the secretion of inhibin and oestradiol-17beta from the gonadotrophin-stimulated ovary.