Ultracytochemical study on the permeability of the human amniotic epithelium

In order to elucidate and characterize the transport pathway of the substances in the amniotic fluid, the permeability of the term human amnion was studied ultracytochemically, with lanthanum or horse radish peroxidase (HRP) as a tracer. Pieces of the term human amnion were exposed to the solutions containing lanthanum or HRP, and processed for electronmicroscopy. Precipitates indicating lanthanum or HRP were observed in the lateral intercellular spaces of the amniotic epithelial cells through the entire depth of the spaces. Generally, pinocytosis of HPR was not observed. In rare cases, however, diffuse uptake of HRP was noticed in the cells of the electron-lucent cytoplasm. These facts indicated that the human amniotic epithelium is quite permeable and that this particular intercellular pathway is important in the mechanism of the transfer of substances between the mother and the fetus.