Calcitonin receptor binding in the hen anterior pituitary during an oviposition cycle

The equilibrium dissociation constant (Kd) and the maximum binding capacity (Bmax) of calcitonin (CT) receptor in the plasma membrane of the anterior pituitary in hens were examined by Scatchard analysis of specific binding of 125I-labeled chicken CT. Values of Kd and Bmax of CT receptor were smaller in laying hens than in non-laying hens. A decrease in the Kd and Bmax value of CT receptor was observed in the anterior pituitary after the injection of estradiol-17β and progesterone into nonlaying hens, but not changed after the injection of 5α-dihydrotestosterone. During an oviposition cycle, the Kd and the Bmax value decreased 3 h before oviposition. In non-laying hens, neither the Kd nor the Bmax value changed during a full day period. The present study suggests that the CT action on the anterior pituitary may increase 3 h before oviposition by the effect of estradiol-17β and progesterone in laying hens.