Localization of progesterone receptors in the shell gland of laying and nonlaying chickens.

The aim of the present study was to localize the progesterone receptor (PR) in the shell gland of the chicken and to determine if the localization and the amount of PR in the shell gland change with egg laying activity. White Leghorn hens laying regularly or out of lay for more than 2 wk were used. Localization of PR in the shell gland was done by immunocytochemistry. The amount of PR in the shell gland mucosal tissues was measured by Western blot analysis. Monoclonal antibodies to the chicken PR, PR6, and PR13 were used in both experiments. The PR were present in the nuclei of the surface epithelial cells, tubular gland cells, stromal fibroblasts, and smooth muscle cells in the arterial wall and myometrium of laying hens. The PR were localized in the same tissues of the shell gland of nonlaying hens as in laying hens. However, the density of PR-positive cells in nonlaying hens was greater, possibly because the tissues were atrophied. Western blot analysis indicated that the amount of PR was greater in nonlaying hens than in laying hens when equal amounts of proteins were used, whereas the molecular weights of PR of laying and nonlaying hens were identical. These results suggest that progesterone acting through its receptor may regulate the secretory activity of the surface epithelium and tubular gland cells for shell formation and the contractile activity of the myometrium. Moreover, once the cells of the shell gland differentiate and become responsive to progesterone, these cells maintain this responsiveness even during the nonlaying period.