Immunohistochemical localization of estrogen receptors in the ovine corpus luteum throughout the estrous cycle.

Using immunohistochemistry and Western blot analysis we attempted to identify the estrogen receptors in ovine luteal cells at different stages of the estrous cycle. Monoclonal antibody against estrogen receptors was used for immunolocalization of estrogen receptor-alpha in corpora lutea sections. Generally, the most intense cytoplasm staining was present in large luteal cells. On the 6th day of the estrous cycle, weak immunostaining of estrogen receptors was observed in large luteal cells as well as in the connective tissue. Luteal cells from regressing corpora lutea expressed the weakest immunostaining. The most intense immunoreactivity for estrogen receptors was found in sections of corpora lutea collected on the 9th day of the cycle. Both, cytoplasmic and nuclear localization was observed depending on cell types in the ovine corpus luteum. Our studies demonstrated the presence of the estrogen receptor-alpha in the luteal cells and suggested an autocrine/paracrine role of estrogen in the regulation of estrous cycle in sheep.