BASIC AND ACIDIC FIBROBLAST GROWTH-FACTOR INCREASE PROLACTIN MESSENGER-RNA IN A DOSE-DEPENDENT AND SPECIFIC MANNER IN GH3 CELLS

In the present report we have studied the effects of acidic and basic molecular forms of the fibroblast growth factor (aFGF, bFGF) on prolactin (PRL) mRNA production and PRL secretion in GH3 cells, a rat pituitary cell line, and their interactions with 17 beta-estradiol (beta E(2)). To meet this purpose we measured mRNA levels in the cells by both Northern blot and dot blot hybridization analysis, and rPRL immunoreactivity in the culture medium by specific RIA. We observed a marked increase in PRL mRNA levels following 24 h incubation with both basic and acidic FGF. This effect was dose-dependent, with maximal responses ranging between 300 and 600% above the control values. bFGF appeared to be much more potent than aFGF (10-50 times), considering the ED(50) of the dose-response curves. Prior incubation with beta E(2) (10(-8) M) produced an enhancement in the responses to low doses of bFGF and aFGF, but not to high doses, as revealed by dot-hybridization analysis. Northern blot analysis showed also that both aFGF and bFGF, may have a partially additive effect with beta E(2) on the mature form (1 kb) of rPRL mRNA in GH3 cells. Considering that bFGF is present at high levels in the pituitary, our results suggest that FGF could be a physiological regulatory factor for prolactin production and secretion.