Monkey pituitary oestrogen receptors and the biphasic action of oestradiol on gonadotropin secretion.

Evidence has been advanced in favour of the hypothesis that, in the rhesus monkey, the negative feedback as well as the stimulatory or so-called "positive feedback" action of oestrogen on gonadotropin secretion is at the level of the pituitary gland. The cellular basis for this biphasic action of oestrogen on the gonadotroph is not understood. In oestrogen target tissues the elicitation of physiological responses is generally associated with the binding of oestrogen to cytoplasmic receptor proteins which are subsequently translocated to the nucleus. Such receptors have been characterized in the anterior pituitary of the rat. In the ovariectomized rhesus monkey refused with 3H-oestradiol, autoradiography and parallel cell fractionation have demonstrated the accumulation of 3H-oestradiol by the nuclei of a significant number of pituitary cells. We describe here some of the properties of these putative oestrogen receptors in the anterior pituitary of the monkey and observe that their distribution between cytoplasmic and nuclear compartments is constant in response to sustained elevations in serum oestrogen concentration which produce a biphasic pattern of circulating gonadotropins.