Reduction of anionic sites on the rabbit uterine surface during the preimplantation period

Studies have been carried out to analyze distribution of anionic sites on the uterine epithelium of the rabbit, using cationized ferritin as a label. A negatively charged glycocalyx was demonstrated by transmission electron microscopy on the luminal cell surface during estrus and days 5–7 of pregnancy. There was a general reduction of labeling from estrus and day 5 to 7 of pregnancy. At estrus and on day 5 and 6 of pregnancy, the results were similar on the meso- and antimesometrial sides of uterine horns and at or between egg recovery sites. At day 7, anionic sites were no longer detected antimesometrially facing the eggs. These results suggested that the progressive loss of anionic sites during the preimplantation period was due to the combined actions of uterus and egg and that this loss might play a role in blastocyst antimesometrial implantation.