Change of the Properties of Follicle Stimulating Hormone like Gonadotropin Binding Sites in the Follicles of the Hen during Follicular Growth

Abstract

FSH (follicle stimulating hormone)-like gonadotropin binding sites in different sizes of follicles in the hen's ovary were investigated by means of radioreceptor assay (RRA), using rat FSH as radioligand. Follicles were divided into five groups, small white follicles (first phase), white colored follicles (second phase), small size yellow follicles (third phase-S stage), medium size yellow follicle (third phase-M stage) and large size yellow follicle (third phase-L stage). As receptors, follicular wall homogenates including theca folliculi and stratum granulosa were obtained from first two groups of follicles, and granulosa cells and theca folliculi were obtained from second and third phase follicles. The binding of radioligands to the binding sites were competitively inhibited by chicken FSH and LH, whereas highly purified rat LH and TSH hardly affected the binding. The FSH-like gonadotropin binding sites were detected in all the receptor preparations tested, and in case of granulosa cells, the binding level increased at the beginning of third phase of the follicle. Scatchard plots analysis suggested the presence of two kinds of binding sites for FSH in first, second and third phase follicles. No major change occurred in the dissociation constant (Kd) of either kind of binding sites during follicular growth. The binding capacity per 10mg tissue, however, varied during follicular growth, exhibiting the highest value in the receptors obtained from follicles of about 10mm in diameter. From these results it is assumed that two kinds of binding sites are present throughout the growth period of the follicle. The number of the binding sites varried during the growth period of the follicle and reached a peak at the early stage of rapid growth phase. The affinity of the binding sites, however, did not change markedly.