Mesodermal alterations induced by hypervitaminosis A

The administration of a single dose (20000 u) of vitamin A by gavage to the pregnant hamster is followed almost immediately by changes in the mesoderm of the embryos. These changes appear 6 h after the administration and after 10 h they have reached their maximum severity. The alterations appear first in the cephalic mesoderm, later in the axial non-segmented mesoderm of the body of the embryo and finally in the somitic mesoderm. They consist of shrinkage of the cell cytoplasm, enlargement of the intercellular spaces (fluid accumulation) and reduction of the mitotic rate of mesodermal cells. These alterations precede the cellular necrosis which appeared later in the somites and is considered a secondary change. An analysis of the embryogenesis of the vitamin A induced skeletal malformation based on the changes described is discussed.