Changes of the luminal surface of the rat uterus at blastocyst implantation

Summary

At day 4 of pregnancy the uterine epithelium possessed regular microvilli and apical protrusions. Ruthenium red stained both a thin layer at the cell membrane and outside this layer, a filamentous region with a thickness of about 0.1 μm. At day 5, the only difference abserved was a more irregular shape of the microvilli and a variation of their size. At day 6, however, the microvilli were replaced by small irregular projections and the apical protrusions nearly had disappeared. Ruthenium red revealed that the filamentous region outside the cell membrane was thicker and more dense than in the previous groups. It is suggested that the change in character both of the ultrastructure of the luminal surface and of its extracellular coat is associated with changed properties of the luminal surface at implantation.