Cytoplasmic Oestrogen Receptor Complex of Female Ovine Pituitary: Changes Associated With the Reproductive State and Oestradiol Treatment

Abstract

Binding of oestrone and oestradiol to a pituitary cytosol receptor was studied in ovariectomized sheep during the breeding season, during anoestrus and after oestradiol treatment during anoestrus. All sheep were ovariectomized 2 weeks before removal of the anterior pituitary. Oestrogen treatment consisted of the subcutaneous implantation of Silastic capsules containing oestradiol-17beta 3 weeks before ovariectomy. Association constants (KA) for oestrone and oestradiol and the concentration of binding sites for oestradiol varied with changes in reproductive state. Oestradiol bound more tightly and the concentration of available binding sites was lower during the breeding season than during anoestrus. The affinity of oestrone binding was less during the breeding season than during anoestrus, whilst the concentration of binding sites for this steroid did not change with changes in reproductive state. Treatment of anoestrous sheeep with oestradiol increased the KA for oestradiol and decreased the concentration of binding sites. However, no effect of oestradiol treatment was observed with regard to the KA or concentration of binding sites for oestrone. The results suggest that either the pituitary oestrogen cytoplasmic receptor undergoes a conformational change during the breeding season causing oestradiol to be more tightly bound or the onset of the breeding season is accompanied by the appearance of a new receptor which binds to oestradiol with greater affinity. Oestradiol treatment of anoestrous sheep mimics this change.

Effects of Bromocriptine and Ectopic Pituitary Transplants on Pituitary and Hypothalamic Nuclear Androgen Receptors in the Male Hamster

“…In the seasonally breeding ewe, the autumnal de creases in plasma PRL levels and the susceptibility of LH release to negative estrogen feedback were reported to be accompanied by an increase [14], a decrease [32], or no change [11] in the pituitary estrogen receptors. It has been suggested that these discrepancies may be related to the confounding effects of the general body condition and the secondary estrogen-binding sites [I], In the female ferret, the cytosolic estradiol binding in the pituitary during the seasonal estrus did not differ from values measured during anestrus [5], Perhaps seasonal changes in the steroid regula tion of gonadotropin release are due primarily to alter ations in the susceptibility of hypothalamic catecholaminergic neurons to steroids [27] rather than to pituitary mecha nisms.…”

Estrogen Regulation of Follicle Stimulating Hormone in Cell Cultures of Sheep Pituitaries1,2

“…There is also much evidence which indicates that estrogens have a major influence on the pituitary directly (2)(3)(4)(5). Indeed, estrogen receptors are found in the hypothalamus (6) as well as in the pituitary (7)(8)(9)(10)(11).…”

“…Ovine LH and the /3-chain of ovine LH were the kind gifts of D. Ward, M.D., Anderson Hospital, Houston, Texas 7. Bovine TSH was the kind gift of J.…”

Cytoplasmic binding of oestradiol-17 in several brain regions, pituitary and uterus of ferrets ovariectomized while in or out of oestrus

“…It seemed possible that changes in the binding capacity or affinity of oestradiol receptors in neurones which mediate the inhibitory feedback effects of this steroid on LH-RH secretion could constitute the postulated resetting of the brain "gonadostat". Wise, Payne, Karsch & Jaffe (1975) reported that in the anterior pituitary of female sheep the concen¬ tration of cytoplasmic binding sites for oestradiol was lower during the breeding season than during the anoestrum, whereas the association constant for oestradiol and its receptor was higher during oestrus. Since all the sheep were ovariectomized 2 weeks before death, seasonal differences in circulating levels of ovarian hormones at the time of death could not have caused these effects.…”

“…Since all the sheep were ovariectomized 2 weeks before death, seasonal differences in circulating levels of ovarian hormones at the time of death could not have caused these effects. Unfortunately, however, Wise et al (1975) presented no information about hypo¬ thalamic binding of oestradiol. Morrell, Ballin & Pfaff (1977) have used autoradiography to monitor the uptake of [3H]oestradiol into the brains of female mink (Mustela vison) which had previously been ovariectomized while in oestrus or anoestrus.…”