Cytochemical studies of uterine and trophoblastic surface coats during blastocyst attachment in the ewe

A glycoprotein coat was demonstrated on the outer surface of both the uterine and trophoblastic cells using ruthenium red, cationized ferritin, concanavalin A-peroxidase and phosphotungstic acid in HCl. No changes were observed on the uterine epithelial surface of cyclic or pregnant animals before or during blastocyst attachment (Day 15). However, the cytochemical reactions were different on the trophoblastic cells of blastocysts at Days 13 and 15, the ruthenium red and cationized ferritin sites of reaction and the concanavalin A receptors being more homogeneously distributed on the outer surface of Day-15 trophoblast. The phosphotungstic acid staining demonstrated a glycoprotein substance between the trophoblast and the uterine epithelium in adhesion areas by Day 18. The results suggest that biochemical changes occur in the composition or distribution of the trophoblastic cell coat during the process of blastocyst attachment in the ewe.