Ouabain-sensitive carrier-mediated transport of glucose from the cerebral ventricles to surrounding tissues in the cat.

1. Artificial cerebrospinal fluid containing isotopically labelled sugars was perfused from the lateral cerebral ventricles to an effluent catheter inserted into the cerebral aqueduct of anaesthetized cats. This system was used for a quantitative study of the absorption of the sugars during steady state.2. A saturable mechanism was involved in the absorption of [U-(14)C]D-glucose and [(14)C]D-galactose. Absorption of [U-(14)C]D-glucose in the dead animal was similar to that of [(3)H]D-mannitol.3. 5 x 10(-5)M ouabain in the inflow reduced cerebrospinal fluid formation and the unidirectional fluxes of glucose from the ventricles into brain tissue and plasma. Ouabain did not alter the absorption of [(3)H]D-mannitol.4. Three types of unidirectional fluxes of glucose from the cerebral ventricles were separated. One was ouabain-sensitive and followed Michaelis-Menten kinetics. The second was insensitive to ouabain and the third occurred by simple diffusion.5. At normal ventricular glucose concentrations (3.5 mM) the three fluxes comprised (roughly): 25% (ouabain-sensitive), 35% (ouabain-insensitive) and 40% (simple diffusion) of total, unidirectional transport.