Effects of castration and estradiol treatment on the postovulatory secretion of follicle-stimulating hormone in the mated rabbit.

Abstract

The effects of castration on the postovulatory secretion of follicle-stimulating hormone (FSH) was measured in mated rabbits. When ovaries were removed at 12 or 18 h postcoitum, FSH increased within 24 h of surgery but without evidence of the previously observed pattern of FSH secretion in the postovulatory period. To prevent the postcastration rise in FSH, various doses of estradiol were injected into does castrated 12 h after mating. Two micrograms estradiol/kg, given daily, was found to prevent the postcastration rise of FSH but was not sufficient to suppress the postovulatory secretion of FSH in intact animals. The postovulatory pattern of FSH release was disrupted in does castrated at either 12 or 18 h postcoitum despite adequate estradiol replacement therapy. Furthermore, in chronically castrated does treated with estradiol (2 micrograms/kg per day), neither mating nor human chorionic gonadotropin (hCG) injection elicited any change in blood FSH levels even though both treatments have been previously found to cause a postovulatory FSH surge. The results of these studies indicate that the ovary, by way of some ovarian secretion, is required for the postovulatory secretion of FSH in the rabbit. The necessary ovarian factor does not appear to be estradiol.