Changes in Calcitonin Receptor Binding in the Shell Gland of Laying Hens (Gallus domesticus) During the Oviposition Cycle

This study was conducted to examine calcitonin (CT) receptor binding in the membrane fraction of the endometrium of the shell gland of laying hens by the use of [125I] CT binding assays. Specific [125I] CT binding was found in the endometrium of the shell gland and increased during the first 1h of incubation and then reached a plateau. Specific [125I] CT binding increased in line with an increase in protein concentration from 20 to 70μg/tube. The membrane fraction had specific binding to [125I] CT. The Scatchard plot analysis revealed a linear profile that indicated the presence of one type of receptor. In egg-laying hens, the equilibrium dissociation constant (Kd) and the maximum binding capacity (Bmax) of the endometrium in the shell gland started to increase soon after oviposition, reached a maximum 19h before the next oviposition and remained high for 8-13 hours. Then it started to decrease 6h before oviposition and reached a minimum at oviposition. In contrast, Kd and Bmax in nonlaying hens were constant throughout the 24h period. These results suggest that CT may not act on the endometrium of the shell gland during most time of the shell calcification period but may act several hours during the last period of calcification as well as post-calcification period.