Diffusion of non-electrolytes in brain tissue

Abstract

The diffusion of urea and creatinine in brain tissue was studied in rabbits using an aqueductal-fourth ventricular perfusion system. The movement of the test solutes in brain tissue conforms approximately to Fick's law of diffusion. It is believed that the computed diffusion coefficients in brain could be similar to their free diffusion coefficients if corrected for the tortuosity of the interstitial channels and the sink effect of the brain capillary bed. The experimental results suggest that there is a relatively open path between the cerebrospinal fluid and brain although the penetration of urea and creatinine molecules during short periods of time is limited to a distance of 100 μm or less from the ependymal surface.