The Inhibitory Effect of Synthetic Steroids on Proestrous Gonadotropin Release in theRat

This study was performed to evaluate the inhibitory effect of synthetic steroids on the hypothalamo-pituitary axis. Six synthetic steroids, used for contraception or other gynecologic indications, were injected to female rats on diestrus 2 (2 mg/kg, sc), and the animals were sacrificed in the afternoon of proestrus. Serum levels of LH, FSH and progesterone, the pituitary contents of LH and FSH, and LH-RH in the median eminence were measured by radioimmunoassays. Among the synthetic steroids tested in this study, norethisterone, d-norgestrel, 3-keto-desogestrel and gestrinone completely blocked the gonadotropin surge on proestrus, showing stronger antigonado-tropic activity than progesterone. Desogestrel did not affect proestrous gonadotropin release at this dose. The suppressive effect of danazol could be seen only in a larger dose (20 mg/kg). These findings reconfirmed previously reported results, which demonstrated that the hypothalamo-pituitary complex was a major site of action of these steroids.