Localisation of glucose transport in the ruminant placenta: implications for sequential use of transporter isoforms.

The facilitative glucose transporters 1 and 3 are the major routes for glucose transport across placental membranes. Using light and electron microscope immunocytochemistry on acrylic sections this study shows a similar pattern of expression from mid to late pregnancy in all four ruminants examined [cow, deer, ewe and goat]. GT1 and GT3 are localised on different membrane layers of the synepitheliochorial placental barrier and glucose must utilise both isoforms sequentially to pass from the maternal to fetal circulations. It is suggested that this arrangement is designed to support the high glucose utilisation by the multilayered placenta in the ruminant.