Glucose transporter GLUT3 in the rat placental barrier: a possible machinery for the transplacental transfer of glucose.

Glucose transfer across the placental barrier is crucial for fetal development. To investigate the role of glucose transporter isoforms in the transplacental transfer of glucose, we investigated the localization of glucose transporters GLUT1 and GLUT3 immunohistochemically in the rat placenta. In the labyrinth, the site of maternofetal exchange of substances, both GLUT1 and GLUT3 were present, whereas only GLUT1 was detected in the junctional region. In the labyrinthine wall, which lies between maternal and fetal circulations, GLUT3 exhibited polarized localization; i.e. it was present at the plasma membranes of the maternal blood side in the syncytiotrophoblast layers. GLUT1 was concentrated at plasma membranes of the maternal and fetal blood sides of syncytiotrophoblast layers. The asymmetric distribution of GLUT3 across the placental barrier may suggest asymmetric transfer of glucose, which would be beneficial to provide a stable milieu for fetal development.