Dexamethasone inhibits the effects of oestrogen on the pituitary gland in rats.

The administration of glucocorticoids has been shown to be effective for the induction of ovulation in patients with anovulation. In the present study, we investigated the effects of a glucocorticoid on oestrogen-induced changes in the pituitary gland. A single ip injection of 10 micrograms oestradiol-17 beta (E2) in ovariectomized and adrenalectomized rats resulted in a significant increase in pituitary weight and progesterone receptor (PgR) concentration. In these animals, serum LH level was initially suppressed and restored to control level 24 h after E2 injection. However, 1 mg of dexamethasone (Dex) injected before E2, but not after E2 administration, completely inhibited both the increases in pituitary weight and PgR concentration. The restoration of serum LH level 24 h after E2 was also prevented. These antioestrogenic effects of Dex were blocked by ip administration of the synthetic antiglucocorticoid, RU486. Dex treatment alone did not have any effect on E2-induced changes in the dynamics of pituitary oestrogen receptor. Finally, E2-pellet implanted sc in ovariectomized and adrenalectomized rats for 7 days caused marked increases in pituitary weight and PgR concentration. A single ip injection of 250 micrograms clomiphene citrate (clomiphene) significantly reduced both the pituitary weight and PgR concentration in these animals, but 1 mg of Dex failed to have a similar effect. These results suggest that glucocorticoids antagonize E2 effects on the pituitary by a mechanism different from antioestrogens such as clomiphene. These antioestrogenic effects of glucocorticoid may be involved in induction of ovulation in anovulatory women.