Basic fibroblast growth factor (bFGF) receptors decrease with luteal age in rat ovarian luteal cells: colocalization of bFGF receptors and bFGF in luteal cells.

Abstract

Ovarian growth factors have been implicated in the development and differentiation of corpus luteum. We have characterized both high and low affinity receptors for basic fibroblast growth factor (bFGF) in luteal cells and tissue throughout the life span of corpus luteum using gonadotropin-treated rat luteinized ovaries. Additionally, we determined bFGF location in luteal tissue. High affinity (Kd, approximately 0.2 nM) and low capacity (approximately 500-6000 sites/cell, depending on luteal ages) [125I] bFGF-binding sites (mol wt, 140 kilodaltons, determined by affinity labeling) were found on luteal cells. [125I]bFGF binding to luteal cells and corpus luteum membranes progressively decreased in binding capacity without affecting binding affinity as the age of corpus luteum advanced. bFGF receptor (flg) mRNA in luteinized ovaries decreased with the luteal age similar to the [125I]bFGF binding. In contrast, low affinity binding sites, identified as heparan sulfate proteoglycans, which were immunohistochemically visualized around luteal cells, did not appear to change with luteal age. The signals for heparan sulfate proteoglycans that were found only in granulosa, but not theca-interstitial, cells of follicles became intense during folliculogenesis. The functionality of the bFGF receptors was shown by tyrosine phosphorylation of 16.5- and 18-kilodalton proteins in luteal cells with the antiphosphotyrosine antibody. Immunohistochemistry localized bFGF to steroidogenic luteal cells, and immunoblotting displayed larger molecular forms of bFGF in luteal cells. These results suggest that the bFGF receptors may be associated with the development and differentiation of corpus luteum in an autocrine manner.