Stimulation of Growth Hormone Release and Synthesis by Estrogens in Rat Anterior Pituitary Cells in Culture

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Abstract
We have investigated the potential effect of estrogens in the control of GH secretion in rat anterior pituitary cells in primary culture. We have found that a 72-h preincubation with 17.beta.-estradiol (E2) caused an approximately 2- to 3-fold stimulation of basal and GH-releasing factor (GRF)-induced GH release as well as cellular GH content at EC50 values of 44, 35, and 15 pM, respectively. Estrone and estriol also increased GH release at respective EC50 values of 100 and 250 pM. The stimulatory effects of these steroids on GH release and cellular GH content were competitively blocked by simultaneous incubation with the antiestrogen LY156758. In contrast to thyroid and glucocorticoid hormones, a 72-h pretreatment with E2 failed to potentiate GRF-induced cAMP accumulation or enhance the sensitivity of the GH response to GRF. However, E2 increased the stimulatory effect of submaximal concentrations of dexamethasone on spontaneous and GFR-induced GH release as well as on total GH, but did not further increase the effect of maximal dexamethasone concentrations. As determined by a 60-min pulse labeling with [35S]methionine performed after a 72-h preincubation with E2, GH and PRL synthesis were increased by about 50% above control values (P < 0.005). The present data clearly indicate for the first time that E2, at physiological concentrations, exerts a stimulatory effect on spontaneous and GRF-induced GH release as well as on cellular GH content, probably resulting, at least in part, from stimulation of GH synthesis.