Effect of monosaccharide on dehydroascorbic acid uptake by placental membrane vesicles.

Dehydroascorbic acid (DHA), the oxidized form of vitamin C, is transported across the microvillous surface of the human placental syncytiotrophoblast by the D-glucose transporter. The existence of this mechanism suggests that maternal hyperglycemia may influence placental transfer of vitamin C. Therefore, we examined the effect of monosaccharides, equilibrated across the membrane, on the uptake of 0.5 mmol/L DHA by placental membrane vesicles. Relative to uptake in the absence of monosaccharide, the rate of DHA uptake was enhanced by up to 90% in the presence of 3-O-methyl-D-glucose equilibrated across the membrane. Comparable results were obtained with D-glucose and D-galactose. An inward-directed monosaccharide concentration gradient inhibited DHA uptake. However, with elevated equilibrium concentrations of monosaccharide, the magnitude of such uptake inhibition was reduced. Relative to DHA uptake at normal blood glucose concentrations (5 mmol/L), the results suggest that moderate maternal hyperglycemia does not alter, but that severe hypo- or hyperglycemia decreases, placental uptake of DHA from the maternal circulation.