Hexose translocation across the blood-brain interface: configurational aspects

The translocation of intravenously administered tritiated 3-O-methyl-D-glucopyranose (3-OMG) into brain has been studied in an intact nephrectomized rat preparation by infusing a series of hexoses into one internal carotid artery. 3-OMG rapidly penetrated into brain with peak concentrations, attained 5-8 min after injection, declining to relatively constant values thereafter. 3-OMG penetration exhibited saturation characteristics as shown by a levelling-off in the rate of translocation as its calculated blood concentration was elevated above 50 m-moles per 1000 ml. Infusion of D-galactose, D-glucose, 2-deoxyglucose, D-xylose and D-mannose significantly reduced the translocation of 3-OMG into brain on the side on which each was infused. D-glucosamine, D-mannitol and D-arabinose were without effect. The phenomenon of countertransport was demonstrated in the nephrectomized rat given tritiated 3-OMG 20 hr prior to infusion of D-glucose or D-mannose into one carotid artery. Each of these hexoses reduced brain 3-OMG concentration on the side on which it was infused. These results support the hypothesis that the translocation of certain hexoses across the blood-brain interface is a carrier-mediated process.