Electron microscopic study of the localization of ferric iron in chorionic epithelium of the sheep placenta

The ferrocyanide method has been used to study, at the ultrastructural level, the maternal-fetal iron transfer in the chorionic epithelium of the haemophagous regions of the sheep placenta during the third trimester of gestation (at the 126th and the 145th day of gestation). No significant differences could be found in the distribution pattern of the ferrocyanide precipitate product with the chorionic epithelium in both stages of gestation. The presence of ferrocyanide reaction product in lysosomal structures, involved in the breakdown of maternal erythrocytes ingested by chorionic epithelial cells, confirmed that trivalent iron is liberated from digested haemoglobin. Ferric iron was also detected in the epithelial cytoplasmic matrix especially in the vicinity of erythrolysosomal structures, between the lateral surfaces of neighbouring epithelial cells, along the complex of interdigitating folds and the basal plasma membrane. Only on one occasion was the presence of ferric iron observed in the basal lamina, between the junctions of the endothelial cells and in their cytoplasmic matrix. The results of the present study indicate that after the ferric iron is liberated from maternal haemoglobin its ionic state, subcellular distribution and, probably, its route of transport seem to be similar to that in the guinea-pig placenta which is characterized by the uptake of iron from maternal transferrin.