Effects of gonadal steroids and cycloheximide on the release of gonadotrophins by rat pituitary cells in culture.

The effects of oestradiol-17beta, testosterone and progesterone alone and together with cycloheximide on the basal and gonadotrophin releasing hormone (Gn-RH)-induced release of gonadotrophins were studied in cultured dispersed rat pituitary cells. In the control group (no steroid treatment), GnRH significantly stimulated the release of LH and FSH; cycloheximide partially inhibited this response, although it had no effect on the basal secretion of gonadotrophins. A dose of 5 ng oestradiol/ml had no significant effect on the response to GnRH; at a dose of 100 ng/ml the GnRH-induced release of LH was significantly augmented whereas the release of FSH was inhibited. Cycloheximide blocked the augmenting effect of oestradiol. The basal release of LH was slightly but significantly inhibited in response to 10 ng testosterone/ml and increased in response to progesterone (200 ng/ml). Testosterone at both dose levels and progesterone significantly inhibited the GnRH-induced release of LH and FSH and in testosterone and progesterone-treated groups, the response to GnRH was inhibited by cycloheximide, but not beyond the levels observed in the control group. It is concluded that steroids can act directly on the pituitary cells, that oestradiol stimulates the GnRH-induced release of LH and that cycloheximide blocks this stimulatory effect. Testosterone and progesterone, on the other hand, partially inhibit the response to GnRH.