Influence of Sex Steroid Hormones on Rat Growth Hormone-Releasing Factor and Somatostatin in Dispersed Pituitary Cells*

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Abstract
The modulatory effects of glucocorticoid and sex steroid hormones on the effects of rat GH-releasing factor (GRF) and somatostatin (SRIF) on GH release and biosynthesis were studied in monolayer cultures of rat anterior pituitary cells with RIA and quantitative immunoprecipitation methods. Dexamethasone (10-7 M), a potent synthetic glucocorticoid, increased both the sensitivity and maxium response of GH release stimulated by GRF. Progesterone (10-7 M) also enhanced GH release stimulated by GRF. The stimulatory effects of dexamethasone and progesterone were dose dependent and required a latent period of at least 24 h to be evident. Testosterone, dihydrotestosterone, and 17.beta.-estradiol showed no apparent influence on GRF-induced GH release under the same conditions. None of the hormones studied showed significant influences on basal or SRIF-suppressed GH release. Progesterone added to the maximally effective concentrations of dexamethasone had no additional effects on GRF-induced GH release. The effect of progesterone was attenuated by both 5.alpha.-dihydroethinodrone, a progesterone antagonist and 17.alpha.-methyltestosterone, a glucocorticoid antagonist. In terms of GH synthesis, stimulatory effects of GRF on GH synthesis were apparent only when pituitary cells were pretreated with dexamethasone. These results indicate that 1) pretreatment with glucocorticoid or progesterone enhances the effects of GRF on GH release and/or synthesis; 2) these two steroids share at least one common step to enhance GRF effects; and 3) steroid hormones have little influence on basal or SRIF-suppressed GH release.