EXPERIMENTAL STUDY Effect of activin on production and secretion of prolactin and growth hormone in cultured rat GH3 cells

Objective: To evaluate the effect of the growth factor activin A on the secretion of prolactin (PRL) and GH in cultured GH3 cells. Methods: The concentrations of PRL and GH secreted from GH3 cells cultured in media with and without activin A were measured by RIA, and the expression of PRL mRNA and GH mRNA were analyzed using the Northern blot method. Results: Activin A significantly inhibited PRL release from GH3 cells cultured for 48 h in a dose-dependent manner (activin: 0.3–3nM). The inhibitory effects of 3nM activin A were observed in the culture from 12 h to 48 h (53.2 % of control). Activin A (3nM) also significantly inhibited the expression of PRL mRNA at 24 h (33.8 % of control). In contrast, activin A significantly stimulated GH release from GH3 cells cultured for 48 h in a dose-dependent manner (activin: 0.3–3nM). The stimulatory effect of 3nM activin A was observed in the culture for 48 h (157.6 % of control). Activin A (3nM) also significantly stimulated the expression of GH mRNA at 24 h (183.6 % of control). In spite of these significant changes in PRL and GH secretion, pit-1 mRNA levels were not significantly changed by activin A. Conclusions: These findings indicated that activin A modulates PRL and GH secretion through the regulation of PRL and GH gene transcription in GH3 cells, but that these effects are unrelated to pit-1 gene expression. European Journal of Endocrinology 142 506–51