Cells of ovarian surface epithelium (OSE) express multiple hormone receptor genes, including those encoding receptors for steroidal and peptidal hormones and localized growth factors. We tested a hypothesis that such receptors mediate an upward expression of proliferation-associated proteins viz. cyatokeratins in cycling ewes. To ascertain a direct effect of the hormones, especially estradiol, progesterone and insuline-like growth factor (IGF), we have chosen cultured OSE cells grown in a serum-free medium.
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For proliferation indication immunocytochemistry with anti-cytokeratin anti-serum was performed, which stained both OSE lining and isolated cells. In serum-free grown cells, foetal calf serum (FCS), fluids from ovine middle and large follicles, and an extract of bovine corpora lutea were added. It was found that FCS enhanced proliferative activity of serum-free cells by 2.5-fold, whereas the follicular and corpora luteal fuids did so to lesser magnitudes.
To understand whether steroidal hormomes in tissue samples were responsible, the fuids were cleaned of steroids by passing through charcoal and yet the proliferative influence was maintained. To confirm that factors other than steroids may be responsible for in vitro proliferative response, serum-free cultured OSE cells were treated with recombinant human IGF-1, estradiol and progesterone at three concentrations.
Only IGF-1 enhanced proliferatin by 2.2-fold. As IGF-1, like HGF, is a localized growth factor, whose expression is stimulated by gonadotropins mediated through their receptors, it was a matter of interest to evaluate whether expression of FSH and LH receptors in OSE cells was similar or different in the OSE layer in proximity to corpus luteum, large preantral follicle and the undifferentiated stroma. About 2-4 fold higher expression in the area close to large follicle indicates that maximum gonadotropin-mediated proliferation takes place just prior to ovulation.