Histological Expression of Metallothionein in the Developing Rat Placenta

Abstract

In order to clarify the metallothionein (MT) localization in the developing placenta, we histologically investigated the sequential MT expression in placentas and fetal livers using pregnant rats during gestation days (GDs) 9 - 21. The placentas were sampled and weighed on GDs 9, 11, 13, 15, 17, 19 and 21. In the early post implantation period, the expression of MT was slightly detected in the yolk sac and the primary decidual zone around the embryo. MT was then mainly present in the deciduas parietalis and yolk sac. After the deciduas parietalis ruptured, MT was subsequently detected in the yolk sac and deciduas basalis. MT continued to be detected in the yolk sac until GD 21, but it was reduced in the deciduas basalis in accordance with development of the fetal liver with elevated MT expression. In conclusion, the main expression site of MT changes from the maternal placenta to the fetal placenta, and then to the fetal liver in accordance with the fetal development. However, we speculate that the MT-positive cells in the placenta are positioned between the maternal and embryonic environments throughout the gestation period and always surround the embryo/fetus.