Endocrinology, Vol 117, 396-404, Copyright © 1985 by Endocrine Society

ARTICLES

Cytochemical and cytophysiological studies of gonadotropin-releasing hormone (GnRH) target cells in the male rat pituitary: differential effects of androgens and corticosterone on GnRH binding and gonadotropin release

RE Tibolt and GV Childs

Steroid hormones can differentially modify gonadotropin release stimulated by GnRH. Decreased GnRH-mediated gonadotropin release has been observed in vitro after pretreatment with androgens or glucocorticoids. In this study, we tested this phenomenon further with the use of a new cytochemical stain for a potent biotinylated analog of GnRH ([Biotinyl D-Lys6]GnRH) combined with stains for LH and FSH and gonadotropin RIAs. The first phase of the study involved characterization of the GnRH target cells in monolayer cultures from male rats. Dose-response curves (measured as the ability to release both LH and FSH) showed that biotinylated GnRH (Bio-GnRH) was equipotent with or more potent than unlabeled [D-Lys6]GnRH in parallel cultures. The avidin-biotin complex stain demonstrated that 16% of the 2- to 3-day pituitary monolayer cells were labeled for Bio-GnRH within 10 min of exposure. Double stains for gonadotropins showed that 37% of the LH gonadotropes and 42% of the FSH gonadotropes did not stain for Bio-GnRH. During the second phase of these studies, the cultures were pretreated for 48 h with 1-100 nM 5 alpha-dihydrotestosterone (DHT), 100 nM corticosterone (CT), or 100 nM epitestosterone (ET) to test the effects of these steroids on the number of cells to which Bio-GnRH bound and the gonadotrope secretory response. Compared with ET- or vehicle-pretreated control cultures, DHT and CT both reduced the amount of LH and FSH release stimulated by GnRH. The magnitude of the reduction in LH release was much greater than that in FSH release, especially after pretreatment with CT. DHT and CT had remarkably different effects on the percentages of cells stained for GnRH. Pretreatment with DHT caused a reduction in the percentages of cells staining for bound Bio-GnRH to 9% compared with 14.3% after CT treatment and 16% after vehicle or ET treatment. The counts of the stained gonadotropes suggested that most of the reduction occurred in the LH gonadotrope population. Because both DHT and CT reduced GnRH- mediated gonadotropin release, but only DHT reduced the percentage of cells that bound Bio-GnRH, it is suggested that the two steroids affect gonadotropin release by separate mechanisms.

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