Alcohol-induced premature permeability in mouse placenta-yolk sac barriers in vivo

Acute alcohol exposure induces malformation and malfunction of placenta-yolk sac tissues in rodents, reducing the labyrinth zone in the placenta and altering the permeability and fluidity of the cell membrane. During normal mouse placentation the cells line up in an optimal way to form a hemotrichorial placenta where layers II and III are connected through gap junctions. These act as molecular sieves that limit the passage of large molecules. PlGF is a developmentally regulated protein that controls the passage of molecules in the vasculosyncytial membranes and media of large blood vessels in the placental villi. In addition to the chorioallontoic placenta, rodents also have another type of placenta that consists of Reichert's membrane within the trophoblast cell layer on the maternal side and the parietal endodermal cells on the embryonic site. This forms a separate materno-fetal transport system. We study here whether alcohol affects these two placental barriers, leading to placental malfunction that in turn diminishes the nutrient supply to the embryo.

CD-1 mice received two intraperitoneal injections of 3 g/kg ethanol at 4 h intervals at 8.75 days post coitum (dpc). The placentas were collected on 9.5, 11.5 and 14.5 dpc and used for histopathological protein studies. Hemotrichorial cell layer structure interactions through connective tissue and gap junction were analyzed by electron microscopy. The permeability of the feto-maternal barrier was visualized with Evans Blue.

VEGF, a permeability inducer, was found to be up-regulated in the mouse placenta after acute alcohol exposure, and permeability was also affected by altered structures in the barriers that separate the feto-maternal blood circulation which destroyed the gap junctions in the hemotrichorial cell layer, reduced the thickness of Reichert's membrane and interfered with with Reichert's trophoblast/Reichert's parietal interaction. These defects together could have caused the permeability malfunction of the placenta-yolk sac tissues as visualized and quantified here by Evans Blue leakage.

An altered PlGF/VEGF ratio together with barrier malformation may contribute to placental malfunction by altering the permeability of the feto-maternal barriers. Further studies are needed in order to show whether premature permeability is involved in the intrauterine growth restriction observed in human FAS embryos.