Brain Edema and Glucose Transport Across the Blood-Brain Barrier

Abstract

When, in order to study the blood-brain barrier (BBB) permeability under varying conditions we only use one indicator substance, we are running the risk of erroneous conclusions. Experiments with one BBB indicator are valuable only when the BBB is damaged or destroyed so that its specific barrier function has become ineffectual. In order to recognize smaller changes of the BBB we have to use several chemical barrier indicators simultaneously. Glucose, being in vivo under normal conditions the sole source of energy for the brain, must be transported across the BBB by a special transport process. So far we know that only a small part of the glucose needed by the brain comes from the blood into the brain by a simple diffusion process. The greater part of glucose is transported by a liver-dependent process. The relation between liver and glucose metabolism has been demonstrated by Geiger and his group in animals (1) and by Bermsmeier in humans (2). There are many arguments that a polysaccharide-containing structure, located at the borderline between the capillaries and the brain tissue, is involved in this glucose transport as an intermediate stage. Relying on the results of Geiger we can assume that this polysaccharide is built up continuously on the BBB’s blood side and broken down at the same time and in the same measure on the brain side. This mechanism may explain the large glucose uptake by the brain without opening the BBB for other substances.