The transport of glucose into the brain of the rat in vivo

A new method, devised to maintain a steady concentration of glucose in the bloodstream, was used to study its influx into the brain of the living rat under sodium pentobarbitone or ether anaesthesia. The findings suggested that glucose entered the brain by a saturable carrier-mediated mechanism with a Km of 7.2 μmol ml-1 and a maximum influx rate of 1.13 μmol min-1 g-1 brain. This mechanism was not affected by the type of anaesthetic used. We did not detect any appreciable passive diffusion of glucose into the brain. There was no movement of glucose between the red cells and the plasma during passage of the blood through the brain. By comparing influx and net cerebral uptake rates it appears that efflux of glucose from the brain occurs, particularly in hyperglycaemic states.