Estrogen receptor immunoexpression in the ovary of the rabbit after ovulation-inducing application of human chorionic gonadotropin

Abstract Background One of the most popular animal species in both animal husbandry and lab work is the rabbit. Consequently, there is a significant need to improve rabbit reproductive performance. Estrogens are responsible for regulating ovarian activities through binding to the estrogen receptors (ER). Therefore, the present study aimed to examine the immunoexpression of estrogen receptors alpha (ERA) and scanning electron microscopy on the rabbit ovary after induction of ovulation. To achieve this aim, thirteen healthy mature female New Zealand white rabbits (2.4 ± 0.1 Kg body weight and 4-5 months old) were induced to ovulate by intramuscular injection of the human chorionic gonadotropin (hCG) (50-70 IU). Ovaries were dissected immediately after slaughtering at 14 hr., 3, 7, and 18 days post-induction of ovulation. The samples were investigated by immunohistochemistry and scanning electron microscopy. Results Our results revealed that ER immunoexpression in the rabbit ovary 14 hr. after induction of ovulation showed strong ER immunoexpression in the ovarian surface epithelial cells and moderate ER immunoexpression in the thin layered ovulation stigma. The pre-ovulatory follicles expressed strong to moderate cytoplasmic and nuclear ER immunosignals in all cell types. The rabbit ovary 3-7 days after induction of ovulation showed strong to moderate ER immunoreactivity in all cell types of the corpus luteum (CL) and of the large antral follicles. The atretic antral follicles showed negative ER immunoexpression in the apoptotic granulosa cells and positive reaction in the proliferated theca interna cells and their surrounding endothelial cells of the blood vessels. The rabbit ovary 18 days after induction of ovulation showed regressed CL with negative cytoplasmic and nuclear ER immunoexpression in the regressed large lutein cells, and in the endothelial cells of the blood capillaries. In addition, moderate cytoplasmic and nuclear ER immunoexpression in the small lutein cells was observed. At all our study periods, we observed that the primordial, primary, growing, and small antral follicles showed moderate cytoplasmic and nuclear ER immunoexpression. At the same time, the interstitial gland cells showed strong cytoplasmic and nuclear ER immunoexpression. Conclusion This work elucidates the role of ERA in the ovarian function (folliculogenesis, ovulation, luteinization) in rabbits which assists in improving the reproductive outcome of this animal. In addition, these findings are increasingly important for implementing a genetic improvement program and utilizing advanced reproductive techniques.