Cortisol regulates secretion and pituitary content of the two gonadotropins differentially in female rats: effects of gonadotropin-releasing hormone antagonist.

To determine if LH and FSH respond to cortisol exposure the same way in females as they do in males, metestrous females were implanted with cholesterol or cortisol (F) subcutaneously, and either ovariectomized or left intact 4 days later. Tail vein injections of 1000 ng of GnRH in saline, or saline alone, were given 4.5, 23.5, or 47.5 h after the time of ovariectomy. Animals were killed 30 min after the injections at 5, 24, and 48 h after surgery. F attenuated the postovariectomy increase in serum LH at 48 h. F also suppressed GnRH-stimulated LH release 24 and 48 h after surgery in ovariectomized animals and in intact animals at 48 h. Pituitary content of LH was increased moderately by F at 5 h. These effects of F are similar to those seen in males. In contrast to LH, F increased serum FSH in intact females and suppressed levels in ovariectomized animals at 24 and 48 h, while inducing a remarkable increase in pituitary FSH content at all three times. These divergent effects of F on serum FSH (suppression in gonadectomized and stimulation in intact groups) were not seen in males, and the increase in pituitary FSH as a result of exposure to F was much more profound and reliable in females than in males. To determine if the F-induced increase in pituitary FSH was dependent on endogenous secretion of GnRH, intact metestrous females were implanted with either cholesterol or F pellets. Each implant group received sc injections of 100 micrograms GnRH antagonist or control injections every 48 h beginning at the time of steroid implantation. Animals were killed 5 days after implantation. The antagonist suppressed both serum and pituitary LH. F also suppressed serum LH levels, but had no effect on pituitary content of LH. Neither the antagonist nor F affected serum FSH. F greatly increased pituitary content of FSH in the presence or absence of GnRH antagonist. These data suggest that 1) LH responds to F treatment in a similar way in females and males; 2) pituitary FSH content is more sensitive to the enhancing effect of F in females than in males; 3) the ability of F to increase pituitary FSH in females is not dependent on GnRH.