Pregnancy and lactation is a critical period for rabbit production. Estrogen (E2) and estrogen receptors
alpha (ERA) are essential during pregnancy and lactation and their importance stems from their
role in ovarian activities. Despite extensive research into the roles of E2 and its receptors in the
ovary, cellular distribution of ERA in the rabbit ovary during pregnancy, after parturition and during
lactation remained unexpectedly elusive. To achieve this aim, eighteen healthy sexually mature New
Zealand white rabbit does (2.97 ± 0.2 kg) were raised in the animal house, faculty of medicine, Assiut
University. The females rabbit were mated by fertile bucks; the day of mating as was considered Day 0
of pregnancy. Ovaries were collected at 12 h, 3, 7, 14 days post-mating, at parturition and at 10 days of
lactation and fixed then processed for immunohistochemistry of ERA. In the present study, the cellular
distribution of ERA in the rabbit ovary during pregnancy, postpartum and during lactation revealed
moderate ERA immunolocalization in the ovarian surface epithelial cells, stroma cells, fibroblast cells
of the tunica albuginea, and follicular cells of the primordial and primary follicles. The growing and
small antral follicles showed strong cytoplasmic and nuclear ERA immunolocalization in the granulosa
cells and theca folliculi cells. The large antral (graafian) and pre-ovulatory follicles showed moderate to
strong ERA immunolocalization in the granulosa cells, corona radiata cells, cumulus oopherous cells,
oocyte, theca interna cells and theca externa cells. The atretic antral follicle showed strong cytoplasmic
and negative nuclear ERA immunolocalization in the apoptotic granulosa cells and strong cytoplasmic
and nuclear ERA immunolocalization in the proliferated theca interna cells. The endothelial cells of the
ovarian blood vessels, the interstitial gland cells and telocytes showed strong cytoplasmic and nuclear
ERA immunolocalization. The corpus luteum (CL) during pregnancy till parturition showed moderate to
strong ERA immunolocalization in the large lutein cells, small lutein cells and luteal endothelial cells.
The regressed CL in the rabbit ovary 10 days of lactation showed weak ERA immunolocalization in the
regressed large lutein cells and moderate cytoplasmic and negative nuclear ERA immunolocalization
in the small lutein cells. Interestingly, the rabbit ovary during lactation showed abundant interstitial
gland with strong ERA immunolocalization in the interstitial gland cells. This work highlights the
role of ERA in the ovulation, folliculogenesis, lutenization and luteal regression in the rabbit during
pregnancy and lactation which contribute to enhancing this animal’s reproductive success.