Timely and topologically defined protein synthesis in the peri-implanting mouse endometrium revealed by light and electron microscopic radioautography.

Many efforts have been made to correlate the morphological and biochemical evidences with changes on physiological state of the uterus during activation of the implantation window. However, the exact mechanism involved in such a phenomenon remains to be determined. The present experiment used the radioautographic approach to determine whether, chronological and/or topological variations of proteins synthesis occur in the peri-implanting endometrium. Pregnant mice submitted to ovariectomy, received exogenous supply of nidatory estradiol. After 0 to 18 hrs. of time-lapsed estradiol effects, each animal received intraperitoneally, 1 hr. pulse 3H-leucine. The uterine fragments embedded in epoxy resin, were processed for light and electron microscope radioautography. The pattern of 3H-leucine incorporation in the luminal epithelium varied according to their relation with the blastocyst present in the uterine lumen. The highest incorporation ratio was seen in the epithelium just around the conceptus 6 hrs. after estradiol treatment, while in the cells localized at interimplantation site no peak of incorporation was seen. At ultrastructural level, cell organelles involved in protein synthesis were found to be labelled. Accumulation of silver grains occurred at apical portion of the epithelial cells showed accumulation of silver grains after 6 hrs. of estradiol treatment, but not on cell surface. The endometrial stromal cells localized around the blastocyst also showed a peak of 3H-leucine incorporation 6 hrs. after estradiol, but not in the cells localized at interimplantation sites. No increased labeling was seen on the components of extra-cellular matrix at ultrastructural level. The present radioautographic experiment showed that epithelial and stromal cells localized in the endometrium of implantation chamber, changed their pattern of protein synthesis under nidatory estradiol effects. This evidence suggests that the phenomenon of implantation window induced by estradiol, is not a systemic response of the whole pregnant endometrium. The activation involves only a specific population of the endometrial cells localized just around the conceptus.