B6 vitamer content of rat tissues measured by isotope tracer and chromatographic methods

Feeding 14C]pyridoxine to growing rats for 146 days produced uniform labelling of the total vitamin B6 pool, thus permitting the radioactivity to be used as an absolute standard for evaluating the accuracy of vitamin B6 analyses. The results demonstrated that trichloroacetic acid extraction followed by cation exchange chromatography accurately measures the B6 vitamers. It is essential to homogenize tissues in a protein-denaturing agent in order to avoid shifts in the vitamer content, particularly in liver. In rats approximately 80% of the radioactivity was found in carcass and 8-9% each in liver and skin. Pyridoxamine phosphate equalled or exceeded the concentration of pyridoxal phosphate in heart, brain and kidney. The total vitamin B6 pool in weanling and adult rats averaged about 16 nmol/g body wt. Meta-phosphoric acid extraction followed by reverse phase chromatography gave good agreement with the cation exchange method in rat liver but with cat plasma yielded pyridoxal phosphate values below those of the cation exchange or enzymatic methods. The discrepancies encountered between different homogenization techniques and chromatographic methods emphasize the need for constant vigilance and continual verification of results by independent methods.