Changes in oestradiol-17beta binding in the hypothalami and pituitary glands of persistently infertile ewes previously exposed to oestrogenic subterranean clover: evidence of alterations to oestradiol receptors.

The binding of [3H]oestradiol-17beta to the hypothalamus and pituitary gland of clover-affected permanently infertile and control ovariectomized ewes was compared in vivo and in vitro. When [3H]oestradiol-17beta was infused into the carotid artery (10 ng/min), the total homogenate and the nuclear and protamine-precipitable cytosol fractions of hypothalami and pituitary glands from clover-affected ewes bound significantly more[3H]oestradiol than those of the controls. Cytoplasmic oestradiol-17beta receptors from the pituitary glands of clover-affected ewes showed a significantly lower apparent association constant and a higher number of binding sites/mg protein in vitro. It is suggested that the hypothalami and pituitary glands of ewes made permanently infertile by oestrogenic clover are less sensitive to feedback regulation of oestradiol-17beta at physiological levels.