Studies of human chorionic gonadotrophin in steroid-primed hypophysectomized rats

The uptake of [125I]HCG was studied in the ovaries of intact and hypophysectomized (Hypox) Sprague-Dawley rats. The [125I]HCG localized specifically in the ovary of the intact rat, and to a lesser extent, in the ovary of the hypox rat. The concentration of HCG in all other tissues and organs of either sex was negligible. However, the localization of [125I]HCG in the hypox rat was enhanced by the presence of exogenous steroids. The greatest increase in HCG uptake was observed in the rats primed with androgen; while a lesser enhancement was demonstrated in the oestrogen treated rats. Comparison of the ovary-to-body weight ratios revealed that a greater amount of HCG localized in the androgen-primed rats than in the oestrogen treated animals even though the ovaries of the former were smaller. These findings suggest that the hypox rat ovary primed with androgen could provide a highly sensitive animal model for further studies of the HCG cell receptor site in animals free of pituitary influence.