Studies on the permeability and enzyme-cytochemistry of the mouse hemotrichorial placenta

The permeability of higher molecular weight substances was investigated in mouse chorioallantoic labyrinthine hemotrichorial placenta, using horseradish peroxidase as a tracer. At the same time, ultrastructural localizations of some important enzymes, such as alkaline phosphatase (ALP), acid phosphatase (ACP), Ca(++)-ATPase and guanylate cyclase were elucidated in this organ by means of the enzyme-cytochemical technique. Peroxidase easily entered the space between layers I and II, and no penetration of this tracer beyond layer II was observed. The reaction products for ALP activity were found mainly on the maternal side of the plasma membrane of the layer II trophoblast. ACP activity was confined to the lysosomes of this layer II cell. In short, peroxidase stopped at the cell surface of the layer II trophoblast, and both ALP and ACP coexisted in this layer II cell. These observations strongly suggest that the layer II trophoblast, especially the surface plasma membrane of this cell, may have an important role in regulating the materno-fetal transfer of substances in mouse chorioallantoic placenta.