In the hen, the preoptic area, medial basal hypothalamus, and anterior lobe of the pituitary showed a greater uptake of [3H]estradiol-17 beta (E2) in vivo than other tissues. This uptake was decreased when unlabeled diethylstilbestrol was injected together with the [3H]E2 or when unlabeled E2 was injected before the [3H]E2 injection. A specific estrogen binding component having properties of a receptor was found in vitro in both soluble and insoluble fractions of these tissues in a hypotonic buffer solution. The administration of E2 in vivo caused a marked decrease in the estrogen receptor binding in the soluble fraction with a concomitant increase in binding in the insoluble fraction; as a result, total binding (sum of the bindings in soluble and insoluble fraction) did not change.

The binding affinity and capacity of arginine vasotocin (AVT) receptor in the hen uterus changed during a period before and after oviposition. Three hours before oviposition, the binding capacity of the AVT receptor increased. An injection of prostaglandin (PG) F2 alpha caused an increase in the AVT receptor Bmax in the uterus, and indomethacin blocked the normal rise in the AVT receptor Bmax and PGF content prior to oviposition. However, just prior to oviposition, the binding affinity increased with a decrease in the binding capacity. A progesterone injection caused an increase in binding affinity and a decrease in binding capacity of the AVT receptor. The specific binding of the progesterone receptor in the uterus increased 2 h before oviposition and remained high until oviposition. Serum AVT levels increased at oviposition. An injection of AVT caused an increase in the affinity of the AVT receptor with a decrease in the capacity. The change in the affinity and capacity of AVT receptor at oviposition may result from the action of progesterone via increased progesterone receptor binding, and the action of AVT on its own receptors.

The cytosol fraction of the anterior lobe of the pituitary in laying White Leghorn hens was shown to possess a progesterone-binding component which perferentially bound progesterone. A similar component was also found in the cytosol of the hypothalamus and of the oviduct magnum. The dissociation constant (Kd) at equilibrium was determined as 1.68 +/- 0.10 (SE) X 10(-10) M in the pituitary, 3.29 +/- 0.10 x 10(-10) M in the hypothalamus, and 3.02 +/- 0.40 x 10(-10) M in the oviduct magnum, whereas the number of binding sites/mg cytosol protein was 5.99 +/- 0.084 (SE) X 10(-13) mol in the pituitary, 0.43 +/- 0.003 x 10(-13) mol in the hypothalamus, and 2.88 +/- 0.114 x 10(-13) mol in the oviduct magnum. The results suggest that a cytoplasmic progesterone receptor is present in the pituitary and hypothalamic tissue, as well as in the oviduct magnum, of the hen.

binding component in the uterus (shell gland) of the chicken. Acta Endocrinol 1992;127:179-84. The plasma membrane fraction of the uterus of the chicken was found to contain a component that shows specific binding to arginine vasotocin (AVT), arginine vasopressin (AVP) and oxytocin (OT). This binding component possesses a higher affinity to AVT than to AVP or OT, and the affinity to AVT was higher in laying hens than in non-laying hens and immature pullets, while the maximum number of binding sites per mg protein was less in the laying hens. Intramuscular injections of either estradiol\x=req-\ 17\g=b\, progesterone or testosterone into the immature pullets for six consecutive days caused an increase in the affinity and number of binding sites. The results suggest that AVT receptors are present in the chicken uterus and that their binding properties are affected by ovarian steroid hormones.In hens, the functional oviduct consists of five distinct regions: the infundibulum, the magnum, the isthmus, the uterus (or shell gland) and the vagina ( 1 ). The uterus consists of the endometrium and the myometrium, and is concerned in the egg shell formation and oviposition (expulsion of an egg) (1). The oviduct develops rapidly after about 16 weeks of age and becomes functional shortly before the onset of egg-laying (about 22 weeks of age) (1, 2).The avian neurohypophysial hormones are arginine vasotocin (AVT) and mesotocin (3). AVT causes con¬ tractions of the smooth muscles of the uterus of the hen (4) during oviposition (5). In mammals, the presence of oxytocin (OT) (6-9) and arginine vasopressin (AVP) (8, 9) receptors in the uterine myometrium has been demonstrated. In birds, however, the presence of the neurohypophysial hormone receptors in any tissue has not been reported. The present experiments were con¬ ducted to demonstrate the presence of a specific binding component having the property of receptor for AVT in the hen uterus, and to elucidate the effect of ovarian steroid hormones on the binding characteristics of this apparent AVT receptor. Materials and methodsHormones and chemicals AVT, mesotocin, AVP, OT, chicken (c) LHRH-II (His5,Trp7,Tyr8-GnRH) and cAngiotensin-II (Val5-angiotensin-II) were obtained from Bachem Inc. (Torrance,

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