Dual role of glucocorticoids in regulation of pituitary content and secretion of gonadotropins.

To verify the inhibitory effect of cortisol (F) on secretion of luteinizing hormone (LH) 24 h postorchidectomy, we implanted cholesterol (C) or F subcutaneously into male rats, and 4 days later orchidectomized or sham orchidectomized them under ether anesthesia. We injected gonadotropin-releasing hormone (GnRH) or saline into these rats 24 h postorchidectomy, collected blood 30 min later, and measured LH and follicle-stimulating hormone (FSH) in serum and pituitaries. F inhibited GnRH-induced secretion of LH without affecting secretion of FSH. We then implanted C, corticosterone (B), or F into rats, performed the same surgeries, and collected pituitaries 24 h after surgery for quantitation of receptors for GnRH. Neither F nor B affected the number of receptors for GnRH or their affinity for a GnRH analogue. Suppression of LH in serum occurred without decreased pituitary content of LH. In contrast, F increased pituitary content of FSH. Implantation of progesterone in a similar experiment did not affect circulating concentrations or pituitary contents of FSH or LH. These data suggest that glucocorticoids may inhibit responsiveness to GnRH by some mechanism distal to the receptor for GnRH that affects only LH.