The presence of a receptor for calcitonin (CT) and the effect of chicken CT (cCT) on adrenocorticotropic hormone (ACTH) secretion stimulated by rat/human corticotropin-releasing hormone (rhCRH) in the hen anterior pituitary were studied. The specific [(125)I]cCT binding component was present in the plasma membrane of hen anterior pituitary and this binding component had properties of a receptor which has binding specificity to cCT, reversibility, saturable binding, high affinity and limited capacity. When anterior pituitary cells were incubated in vitro, cCT increased the maximal secretion of chicken ACTH stimulated by rhCRH. These results suggest that CT may act directly on the anterior pituitary via its receptor binding and enhances the ACTH secretion by CRH.

The present study was performed to elucidate whether the receptor for calcitonin (CT) exists in the adrenocortical cells of hens and to determine the effect of CT on adrenocorticotropic hormone (ACTH)-stimulated corticosterone production in its cell. The binding site of CT in the membrane fraction of the adrenal gland in hens was determined using a [125I]CT binding assay system. The binding properties in the adrenal gland satisfied the criteria of a receptor-ligand interaction in terms of specificity, reversibility, and saturation. When the cortical cells were incubated in vitro with chicken ACTH in the presence of CT, greater corticosterone production was observed. The result suggested that CT acts directly on the adrenocortical cells via its receptor binding and increases responsiveness of ACTH on corticosterone production in the laying hen.

The presence of the receptor for parathyroid hormone-related peptide (PTHrP) and the effect of PTHrP on adrenocorticotropic hormone (ACTH) secretion in the hen anterior pituitary were examined. The plasma membrane fraction of the anterior pituitary was found to contain a specific chicken PTHrP (cPTHrP) binding component. The binding component had properties of a receptor, such as binding specificity to cPTHrP, reversibility, saturable binding, high affinity, and limited capacity; therefore, it was elucidated that the PTHrP receptor exists in the plasma membrane of the hen anterior pituitary. A third ventricular injection of cPTHrP in nonlaying hens caused a decrease in the chicken ACTH level of the anterior pituitary and an increase in the chicken ACTH level of blood plasma, with an increase in the binding affinity and a decrease in the binding capacity of PTHrP receptor in the anterior pituitary. The present study suggests that PTHrP may act directly on the anterior pituitary via its receptor binding and may enhance ACTH secretion from this tissue in hens.

The present study was performed to demonstrate the presence of receptors for avian calcitonin (cCT) in ovarian granulosa cells of the largest follicle of laying hens and to determine the e ect of cCT on LH-stimulated P production. The cCT binding in the granulosa cells of the largest follicle was determined using a [ I]CT binding assay. The binding properties in the granulosa cells satisfied the criteria of a receptor-ligand interaction in terms of specificity, saturation, high a nity and limited capacity. During incubation of ovarian granulosa cells cCT alone did not a ect the P production alone, but cCT decreased the amount of LH-stimulated P production and the sensitivity to LH. The present study suggests that cCT may act directly on the granulosa cell of the largest follicle via its receptor binding and inhibit P production in response to LH in hens.: calcitonin, hen, graulosa cell, ovary, progesterone gland in the avian species (Copp and Cheney, , Finney, calcium homeostasis (Stevenson ) and CT receptor determine the e ect of CT on LH-stimulated P production.terone production in the granulosa cells of the ovary (Tsai, lating hormone (FSH; Furr, ). The progesterone (P ) exists in the uterus, and the CT acts on this tissue end of the period for the egg-shell formation (Ieda ). Calcitonin (CT), a hormone consists of a amino acid Therefore, it is considered that the CT regulates egg-shell peptide, and primarily secreted from the ultimobranchial formation even previous findings regarding to the change in the blood CT level has not been identified in chickens. ; Kenny, ). CT is considered to maintain the It has been reported in mammals that CT inhibits progesbinding in the shell gland (uterus), bone and kidney ). In birds, vasoactive intestinal polypeptide di ers between laying hens and nonlaying hens (Ieda (VIP) (Törnell, ; Johnson and Tilly, ; ; Yasuoka ). Laying hens and nonlaying Johnson, ) and melatonin (Webley and Luck, hens di er in ovarian function (Kawashima ) ; Murayama ) stimulate P production in including production of sex steroid hormones which are the granulosa cells. It is known that P concentration is regulated by luteinizing hormone (LH) and follicle stimuthe highest in the largest follicle (Shahabi ). However, the physiological relationship between CT and level in blood reaches a peak approximately h before P .is not obscure. The present study was performed to oviposition with a peak of LH level (Furr, ). The demonstrate the presence of receptors for CT in ovarian receptor for P exists in the uterus (Kawashima granulosa cells of the largest follicle in laying hens and to a), and a peak of the amount of P receptor is found h to h before oviposition (Kawashima b). This is a period when calcium is transferred to the uterus to form the egg-shell. Furthermore, Kawashima ( b) suggested that P could be involved in the eggWhite Leghorn hens ( to mo of age; . to . kg shell formation during this period. The CT receptor also of BW) laying five or six sequences for more than weeks were kept in individual c...

To demonstrate the presence of a receptor for calcitonin (CT) in the hen neurohypophysis and to estimate the time of action of CT on the neurohypophysis during the oviposition cycle in relation to arginine vasotocin (AVT) release, binding of (125)I-labeled chicken CT in plasma membrane fractions of the hen neurohypophysis was measured by the use of a radioligand binding assay. The binding specificity, reversibility, high affinity, and limited capacity are characteristics of a CT receptor. Therefore, it was elucidated that the CT receptor might exist in the plasma membrane of the neurohypophysis of hens. The binding affinity of CT receptor increased at 30 min before oviposition and the binding capacity was decreased at 15 min before oviposition. However, no change was found in non-laying hens during a 24-h period. Such changes in the CT receptor binding were found at 10 min after an i.v. injection of chicken CT into non-laying hens with an increase in the blood level of AVT. The changes in the binding affinity and capacity of CT receptor of the neurohypophysis may be related to AVT release partly at oviposition time in the hen.