Blood-brain transfer of glucose and other molecules measured by rapid indicator dilution.

YUDILEVICH, D. L., AND NORINA DE ROSE. Blood-brain transfer of glucose and other molecules measured by rapid indicator dilution. Am. J. Physiol. 220(3) : 841-846. 197 1 .-The blood-brain barrier (BBB) of the dog was studied in vivo, by means of the first-passage multiple-tracer dilution technique. Venous samples were obtained at the rate of 3-5/set, for about 5 sec. The labeled molecules used were hemoglobin, sucrose, mannitol, Dand I,-glucose, glycerol, urea, sodium, chloride, rubidium, and water. The results suggest that hemoglobin has a shorter transit time than the other molecules (Taylor’s effect). All substances, except water that diffuses readily (capillary extraction 0.90) and D-glucose, appear to be confined to the sucrose space which, in a first passage through the cerebral circulation, means the vascular space. DGlucose-3H fractional extraction E (with sodium 22 as intravascular reference), ranged between 0.15 and 0.54, while simultaneously measured E for L-glucose14C was zero. D-Glucose extraction was reduced when the concentration was increased. These results support the hypothesis that glucose is transported through the BBB by a facilitated mechanism located either in the capillary endothelium or in the glial capillary investment.