Changes in Parathyroid Hormone-Related Peptide Receptor Binding in the Shell Gland of Laying Hens (Gallus domesticus) during the Oviposition Cycle

Abstract

In this study, parathyroid hormone (PTH) receptor binding was examined in the membrane fraction of the endometrium of the shell gland of laying and nonlaying hens by the use of 125I-PTH-related peptide (PTHrP) binding assays. Specific 125I-PTHrP binding was found in the endometrium of the shell gland and increased during the first 1 h of incubation and then reached a plateau. Specific 125I-PTHrP binding increased in line with an increase in protein concentration from 10 to 80 μg. The membrane fraction had specific binding to 125I-PTHrP. The Scatchard plot analysis revealed a linear profile that indicated the presence of one type of receptor. The equilibrium dissociation constant (Kd) and the maximum binding capacity (Bmax) in the shell gland decreased 19 h before oviposition in egg-laying hens and remained low for about 20 h during the period of calcification. In contrast, the Kd and the Bmax in nonlaying hens were constant throughout a 24-h period. These results suggest that PTH acts on the endometrium of the shell gland during the eggshell calcification.