Red blood cell as glucose carrier: significance for placental and cerebral glucose transfer.

At plasma glucose values of 5 mM (90 mg/100 ml) the maximum glucose transport capacity of the human red cell membrane is 12,000 times the rate of glucose utilization by the red blood cell. Mammals, other than primates, that have been tested have a comparable high-capacity system during fetal life, which is lost soon after birth. It has been suggested that the availability of the water space of the red blood cell for distribution of glucose facilitates transfer across the placenta during fetal life in all mammals and across the blood-brain barrier in adult primates. Though plausible, more comparative studies of glucose transport in red blood cells of other species and direct experimental evaluations of the contribution of the red blood cell to glucose transfer across the placenta and the blood-brain barrier are needed.