Influence of gonadal steroids on rat pituitary growth hormone secretion

Growth hormone (GH) secretion increases at the time of puberty, and both androgens and estrogens increase the GH response to provocative agents. Little is known, however, with regard to the mechanism or site of action of gonadal steroid-stimulated GH secretion. Using monolayer primary cell culture and radioimmunoassay techniques, insulin-like growth factor I (IGF-I), purified and biosynthetic human GH, 17 beta-estradiol (E2), and testosterone (T) effects on GH release from rat anterior pituitary cells were investigated. Media content of rat GH was measured, both basally and after growth hormone releasing factor (GRF) stimulation. IGF-I at 50 nM concentration inhibited basal rGH release but not in GRF-stimulated cells. E2 (10 pM) stimulated basal secretion of rGH, although higher concentrations did not. High concentrations of T (100,000 pM) caused an increase in GRF-stimulated rGH secretion. Neither purified nor biosynthetic hGH pretreatment influenced subsequent rGH release. These results suggest that IGF-I inhibits and E2 (low dose) and T (high dose) augment rGH release in part at the level of the anterior pituitary.