Calcitonin Directly Inhibits Luteinizing Hormone-Stimulated Progesterone Production in Granulosa Cells of the Largest Follicle of Hen

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 effect of cCT on LH-stimulated P4 production. The cCT binding in the granulosa cells of the largest follicle was determined using a [125I]CT binding assay. The binding properties in the granulosa cells satisfied the criteria of a receptor-ligand interaction in terms of specificity, saturation, high affinity and limited capacity. During incubation of ovarian granulosa cells in vitro, cCT alone did not affect the P4 production alone, but cCT decreased the amount of LH-stimulated P4 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 P4 production in response to LH in hens.