I mmunohistochemistry of Hypothalamic GN RH Following Manipulation of Sex Steroid Levels: Evidence that Androgens have Divergent Effects on GNRH Stores and Serum Follicle Stimulating Hormone Levels1, 2

Abstract

Immunohistochemical visualizations of GNRH in the median eminence were correlated with measurements of circulating gonadotropin levels in rats. In one experiment, 4 days of treatment with Silastic capsules of 5α-dihydrotestosterone (DHT:8 or 48 mm/100 g BW) or testosterone (T:48 mm/100 g BW) were initiated 34 days after gonadectomies on Days 2.23 or 45 of life. The visually determined intensity of GNRH staining was diminished in gonadectomized rats when compared with that observed in age matched intacts or steroid-treated rats. T always suppressed the elevated serum levels of both FSH and LH. DHT suppressed serum gonadotropins in all orchidectomized rats, serum LH in all ovariectomized rats, serum FSH in rats ovariectomized on Day 2, but not in rats ovariectomized on Days 23 or 45. In another study, using rats ovariectomized as adults. DHT or estradiol benzoate (EB) treatment partially restored the GNRH staining. While EB suppressed both FSH and LH[unknown] DHT suppressed serum LH and elevated serum FSH. These discrepancies in the simultaneous effects of DHT on GNRH staining and serum FSH levels suggest that FSH secretion may be regulated, in part, by a FSH-regulating neurohormone or that DHT may act at the pituitary to increase serum FSH in ovariectomized rats.