Changes in localization of ovarian immunoreactive estrogen receptor during follicular development in hens

The aim of this study was to examine the changes of ovarian estrogen receptor (ER) localization in hens to determine the significance of estrogen-ER interactions for the regulation of follicular functions during their development. The ER was localized by immunocytochemistry in the various developmental and regressing stages of follicles, namely cortical and white follicles, the largest (F1, matured follicle) and third largest preovulatory follicles (F3, rapid growth phase follicle), and post-ovulatory follicles (POF). No immunoreaction for ER was observed in the cortical follicles, whereas the interstitial cells in the outer theca externa were ER positive in white follicles. The islets of epithelial cells (identical to estrogen producing cells) in the outer theca externa and granulosa cells were ER positive in F3 follicles. These ER immunoreactions observed in F3 follicle were remarkably reduced in F1 and POF. These results suggest that estrogen-ER interactions may be responsible for the follicular growth, and the loss of ER may be involved in the mechanism of follicular maturation. The estrogen-ER interactions may be also involved in the local control of the steroid production in follicles.