Abstract
Abstract— The total concentrations of vitamin B6 (B6) in plasma, choroid plexus, CSF and brain of adult New Zealand white rabbits, measured fluorometrically, were 0.30, 15.10, 0.39 and 8.90μmol/l or kg respectively. The mechanisms by which B6 enters and leaves brain, choroid plexus and CSF were investigated by injecting [3H]pyridoxine (PIN) intravenously, intraventricularly and intraarterially. [3H]PIN, with or without unlabelled PIN, was infused intravenously at a constant rate into conscious rabbits. At 150 min, [3H]B6 readily entered CSF, choroid plexus and brain. The addition of 0.5 mmol/kg carrier PIN to the infusion solution depressed the relative entry of [3H]B6 into CSF, choroid plexus and brain by about 80%. After intraventricular injection, [3H]PIN readily entered brain from CSF. The intraventricular injection of carrier PIN with [3H]PIN decreased the amount of [3H]B6 in brain and also decreased the percentage of [3H]B6 in CSF and brain that was phosphorylated. During one pass through the cerebral circulation, [3H]PIN (1 μm) was cleared from the circulation no more rapidly than mannitol. These results were interpreted as showing that the entry of B6 from blood into CSF and presumably the extracellular space of brain and thence into brain cells involves one or more saturable transport and/or metabolic steps.
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