EFFECT OF HYPOPHYSECTOMY ON BINDING OF HUMAN CHORIONIC GONADOTROPHIN TO IMMATURE AND ADULT RAT OVARIES

Abstract

The binding of 125I-labelled human chorionic gonadotrophin (HCG) to ovarian tissue was studied in hypophysectomized immature and adult rats. The ability of the ovaries of adult rats to bind HCG was markedly reduced within 3 days of hypophysectomy and remained low for at least 20 days. The extent of the reduction depended on the stage of the oestrous cycle at which hypophysectomy was performed. The highest loss of HCG binding capacity was seen in rats hypophysectomized at dioestrus II, while rats hypophysectomized at the oestrous stage exhibited similar HCG binding to control rats at the same stage of the cycle. Scatchard analysis indicated that the reduction in the capacity of the ovary to bind HCG after hypophysectomy was caused by the loss of specific receptors and not by a decrease in binding affinity. In contrast to adult rats, in immature rats the HCG binding capacity of the ovaries did not change during the 3 days after hypophysectomy, but after this a slow decline took place. Twenty days after pituitary ablation, almost identical values for binding of HCG were found in immature and adult rats. Since hypophysectomy in adult rats causes a rapid regression of large follicles, our results indicate that the remaining HCG binding activity arises largely from small follicles which are known to be unaltered by the deprivation of hypophysial hormones. This assumption is supported by our observation that in the ovaries of 25-day-old immature rats, which lack large follicles, only a slow decrease in the ability of the ovaries to bind HCG occurs in the 20 days after the operation.