Inhibition of the first ovulation and ovarian prostaglandin F2 alpha metabolism by danazol in rats.

The present study was conducted to investigate the mode of action of danazol by monitoring the first ovulation, serum luteinizing hormone (LH) levels and ovarian prostaglandin (PG) F2 alpha metabolism in pregnant mare serum gonadotropin (PMSG)-primed immature female rats. When danazol (750 mg/kg) was given p.o. once a day for 5 days (day 24-28), the occurrence of the first ovulation, the increase in capacity to form 13,14-dihydro-PGF2 alpha and PGF2 alpha levels induced by PMSG (5 IU) injected on day 26 were clearly inhibited on day 29. Danazol also markedly suppressed the LH surge occurring on day 28. Although the danazol-induced blockage of ovulation was restored by injection of human chorionic gonadotropin, the number of oocytes was significantly decreased as compared with that of controls. The present data indicate that the inhibitory actions of danazol on ovulation and ovarian PGF2 alpha metabolism may occur via some direct effects on the ovary in addition to the suppression of gonadotropin release from the pituitary gland.