A nonmitogenic pituitary function of fibroblast growth factor: regulation of thyrotropin and prolactin secretion

The addition of fibroblast growth factor (FGF) to primary cultures of rat anterior pituitary cells modifies their response to thyrotropin-releasing factor in a dose-dependent manner. While the pituitary response to the other releasing factors (corticotropin-releasing factor, growth hormone-releasing factor, and gonadotropin-releasing factor) is not altered, FGF increases both the sensitivity of the cells to thyrotropin-releasing factor and the amounts of prolactin and thyrotropin released. A minimum of 24 hr of preincubation with FGF is required to modify the pituitary response, and maximal effects were observed with 48 and 72 hr of preincubation. The effective doses of FGF are similar to those described for its mitogenic activity (i.e., 1-100 pM), but inhibition of cell growth with 5-fluorodeoxyuridine does not modify the effect of FGF on thyrotropin and prolactin release. These results suggest a novel paracrine, if not autocrine, role of pituitary FGF in the homeostatic mechanisms that regulate the secretion of prolactin and thyrotropin. They also suggest that the biological significance of the presence of FGF in various tissues may not be directly related to its in vitro mitogenic activity.