Metabolism of Tritium‐labelled Pyridoxine and Pyridoxine 5′‐phosphate in the Central Nervous System¹

Abstract— [ 3 H]Pyridoxine and [ 3 H]pyridoxine 5′‐phosphate have been injected into rats and mice. The uptake in brain tissue has been studied by comparing the concentrations of labelled compounds in serum, cerebrospinal fluid and brain tissue. Labelled pyridoxine passes rapidly into brain tissue, whereas the uptake of pyridoxine 5′‐phosphate occurs at a much slower rate. Perchloric acid extracts of brain have been fractionated by ion‐exchange chromatography and the distribution of isotope between the different forms of the vitamin has been determined at different times after the administration. The time sequence of the metabolic transformation is: pyridoxine+→ pyridoxine 5′‐phosphate → pyridoxal 5′‐phosphate → pyridoxamine 5′‐phosphate. After the initial transformation period about 40 per cent of the isotope is recovered in each of the pyridoxal 5′‐phosphate and pyridoxamine 5′‐phosphate fractions.