CHANGES IN UTERINE ESTROGEN AND PROGESTERONE RECEPTORS DURING DELAYEDIMPLANTATION AND EARLY IMPLANTATION IN THE SPOTTED SKUNK

Although the exact cause(s) of embryonic diapause in the western spott ed skunk and other carnivores remains unknown, it has been hypothesize d that it may be due to levels of ovarian hormone secretion that are i nsufficient to promote a uterine environment conducive to continuous e mbryonic development and implantation. Immunocytochemistry was used to determine whether changes in abundance or distribution of estrogen re ceptors (ER) and progesterone receptors (PR) may be associated with th e cessation or renewal of embryonic development. Thirty pregnant skunk s were killed during delayed implantation and periimplantation periods . ER and PR were detected in luminal and glandular epithelium, endomet rial stroma, vasculature, and myometrium of the uterus during the peri od of delayed implantation. There was a significant reduction of both ER and PR receptors during the periimplantation period. The most prono unced change was the complete loss or reduction in staining intensity for PR and ER in the luminal epithelium during the first 2-3 days afte r implantation. These findings suggest that the failure of skunk blast ocysts to undergo continuous development and implant without a prolong ed period of diapause is not the result of an insufficient number of E R or PR in the uterus. The data also indicate that renewed embryonic d evelopment and implantation is not associated with an increase in thes e uterine steroid receptors.