Influence of Corticosterone on the Response to Gonadotropin-Releasing Hormone in Rats

Abstract

The objective of this study was to determine whether the diurnal rhythm of corticosterone (B) alters the response of the pituitary to gonadotropin-releasing hormone (GnRH). Mature female rats housed in constant illumination were ovariectomized (Ovx) and adrenalectomized (Adx), and maintained on either corticosterone (B, 160 μg/ml in drinking water) or 0.9% saline. 3 weeks later a silastic implant of estradiol (E2) was implanted subcutaneously into each animal. For the next 5 days B-maintained rats received a daily injection of either B (250 μg/100 g BW) or vehicle at 05.00 or 17.00 h. Groups of rats were sacrificed at 0, 1, 3, 6, 12 and 18 h after the fifth injection, and plasma B and E2 were measured. Other animals were challenged with GnRH (1.0 ng/100 g BW) at 0, 6, 12 and 18 h after the last B injection. The fifth B injection initiated changes in plasma B which closely mimicked the normal B rhythm in intact rats. E2 levels (approximately 100 pg/ml) remained fairly constant over the same period. In rats receiving B injection at 17.00 h, the response to GnRH was altered by B administration. The LH response was greatest 6 h after B was injected, and animals showed a lower response at other times. The same relationship between circulating B and the response to GnRH could not be demonstrated in rats injected with B at 05.00 h. Animals maintained on saline exhibited higher basal LH levels, a longer mean half-life of LH, and the plasma LH response to GnRH was lower than in animals receiving B therapy. These results indicated that: (1) physiological dosages of B can alter the response to GnRH in constant light rats; (2) B has a potentiating effect on this response, and (3) B may also influence the clearance rate for LH.

Corticosteroid Regulation of Gonadotropin Secretion and Induction of Ovulation in the Rat

“…Direct stimulatory effects on gonadotropin secretion by both cortisol and corticosterone have been demonstrated in pituitary cell culture studies (6)(7)(8). In vivo studies have reported variable and contradictory results indicating that the glucocorticoid effect is largely inhibitory to gonadotropin secretion (9-1 1).…”