Estrogens, cyclic adenosine 3',5'-monophosphate, and phorbol esters modulate the prolactin response of GH3 cells to basic fibroblast growth factor.

The effects of basic fibroblast growth factor (bFGF) on the secretion of PRL and GH by a cell line derived from a rat pituitary tumor (GH3 cells) were examined. The interactions between bFGF and compounds that are known to modify the activity of GH3 cells (estradiol, cAMP, and phorbol esters) were also studied. bFGF has little effect on cell growth or on the secretion of GH by GH3 cells but specifically increases the capacity of the cells to release PRL. The effect is time and dose dependent and reaches maximal levels with a 24-h preincubation of the cells with bFGF. The effects of bFGF on PRL secretion are potentiated by the addition of estradiol (maximally effective dose 100 pg/ml approximately 10(-10) M) and are further increased by the addition of the phorbol ester, phorbol myristate acetate. The results indicate that, like in normal lactotrophs, bFGF has a major influence on the release of PRL by tumor-derived GH3 cells. The results support the hypothesis that bFGF may play an important paracrine, if not autocrine, role in regulating the PRL-secreting cells of the pituitary. The potential use of GH3 cells to elucidate the mechanism through which bFGF modulates differentiated cell function is discussed.