THE DISTRIBUTION OF INTRAVENOUSLY-INJECTED INULIN IN THE FLUIDS OF THE NERVOUS SYSTEM OF THE DOG AND RAT*

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Abstract
Inulin solutions were injected intravenously into previously nephrectomized dogs and rats. In the dogs, after periods of time not less than 3hr., a comparison of the inulin level in the serum and in the cerebrospinal fluid showed that the blood-cerebrospinal fluid barrier was relatively impermeable to inulin. On killing both the dogs and the rats, an analysis of the brain tissue for inulin and its comparison with the serum level permitted an estimation of the inulin space of the brain tissue which was found to be less than 5% of the wet weight of the tissue. This suggested that the blood-brain barrier was also relatively impermeable to inulin. It is suggested that the absence of an extracellular fluid phase in the brain as it exists in other body tissues might serve to explain how inulin and many other substances fail to penetrate the brain fluids.