Permeability of Brain Capillaries to Hexoses and Pentoses in the Rabbit

The initial loss in the rabbit brain of non-electrolytes injected into the carotid artery was measured with ‘Indicator Diffusion’ technique, 3–0–methyl-D-glucose shared with D-glucose the ability to pass into the brain by a mediated transport mechanism. The rate of transport of the following substances could not be distinguished: D-mannose, D-galactose, D-arabinose and 1)-ribose. They all penetrated more slowly than D-glucose. D-mannitol was also lost from the blood during the passage through the brain. This observation, together with the known inability of D-mannitol to pass the blood-brain barrier, suggests that the loss takes place into the endothelial cytoplasma. Thus the basal plasma membrane of the endothrlial cells together with the basal membrane proper may define blood-brain barrier chararteristirs.