Calcitonin receptor binding in the hen neurohypophysis before and after oviposition

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 nonlaying 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 nonlaying 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.