Immunocytochemical localization of vitamin D receptors in the shell gland of immature, laying, and molting hens.

It is accepted that vitamin D is involved in the control of egg calcification in hens. The goal of this study was to localize the vitamin D receptors (VDR) in hen shell gland and to determine whether their localization was dependent on reproductive function. Frozen sections of the shell gland of immature, laying, and molting hens were immunostained for VDR, and the VDR in these tissues were also examined by Western blot analysis. Both apical and basal cells of the mucosal epithelium as well as tubular gland cells showed a strong immunoreaction for VDR in the shell gland of laying hens. In the magnum and isthmus, the basal cells of the mucosal epithelium showed a moderately strong immunoreaction for VDR, whereas the immunoreactions in the apical cells of the mucosal epithelium and tubular gland cells were weak. In the shell gland of immature birds, both the mucosal epithelium and tubular gland cells showed a moderately strong VDR immunoreaction. In molting hens, the mucosal epithelial cells and tubular gland cells showed a strong VDR immunoreaction although the mucosal tissue was regressed. Western blot analysis indicated that the mucosal tissue of the shell gland of immature, laying, and molting hens contained two forms of immunoreactive VDR, which were approximately 58 and 60 kDa. Because VDR were richer in the shell gland than in other oviductal segments, these results suggest that in laying hens the shell gland tissues are one of the significant targets for vitamin D. It is likely that the amount of shell gland VDR increases during sexual maturation and immunoreactive VDR remain even during the molting phase.