Estradiol “receptors” in hypothalamus and anterior pituitary gland: Inhibition of estradiol binding by sh-group blocking agents and clomiphene citrate

Abstract

Estrogen-sensitive tissues selectively take up and retain estradiol and other biologically active estrogens by binding them to “receptors ” present in cytoplasm and nuclear fractions. Such “receptors,” already isolated from myometrium and endometrium of several species, should be present in pituitary gland and hypothalamus if binding of the hormone is analogous and also necessary for its specific biological activity in these tissues. To test this hypothesis, we incubated various bovine hypothalamic tissues and pituitary glands with 3Hestradiol (10-10 to 10-9M) and isolated the radioactive steroid “receptor” complex by density gradient ultracentrifugation. The amount of “receptor”-bound radioactivity present in fractions 1-10 of the gradient was greatest with cytoplasm of pituitary gland and decreasing amounts were observed in median eminence, paraventricular portions of the anterior and posterior hypothalamus and little if any specific binding occurred with that of the parietal cortex. Binding of neither radioactive progesterone nor testosterone was seen in these fractions obtained from either adult females or steers. Sulfhydrylgroup blocking agents, p-chloromercuriphenyl sulfonic acid (0.003M) and N-ethylmaleimide (0.007M), and clomiphene citrate (10-7 to 10-5M) consistently inhibited the binding of estradiol. The physiological significance of estradiol binding to “receptors” in hypothalamus and pituitary gland remains unknown but these findings are consistent with current hypotheses about pituitary- gonadal physiology. © 1970 by The Endocrine Society.