Bidirectional placental transfer ('leak') of L-glucose in control and diabetic rats

The placental transfer of D- and L-glucose was investigated in anaesthetised non-diabetic and streptozotocin-induced diabetic rats. Maternal to fetal transfer was determined by perfusing the fetal side of one placenta in situ whilst infusing a mixture of D-[3-3H]glucose and L-[1-14C]glucose into the maternal circulation. Back-transfer from the fetal to maternal circulation was assessed by determining the uptake of the radiolabelled glucoses from the perfusion fluid during a single passage through the placenta on the fetal side. Maternal diabetes resulted in a reduced utero-placental blood flow but an increased bidirectional transfer of D-glucose. Non-specific maternal to fetal placental transfer of L-glucose was greater in diabetic rats than in controls, and the loss of L-glucose during placental perfusion on the fetal side was, again, greater in diabetic than in control rats. This increased bidirectional 'leak' of glucose possibly reflects a functionally compromised placenta, caused by its formation in a diabetic milieu, and may explain the greater fetal-maternal glucose ratios found in diabetic rats relative to controls.