Metabolism of Tritium- and14C-Labeled Pyridoxine in the Rat

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Abstract
Studies on the metabolism of different forms of vitamin B6 in vivo require the use of labeled compounds with high specific radioactivity. Tritium-labeled pyridoxine has therefore been used in several studies. Since tritium is lost in the metabolic conversion of pyridoxine, we have now determined the distribution of tritium in [3H8] pyridoxine prepared by exposure of pyridoxine to tritium gas and compared the metabolism of [3H8] pyridoxine in rats with that of [4,5 – 14C2] pyridoxine. Oxidation of [3H8, 4, 5 – 14C2] pyridoxine with potassium permanganate to 4-pyridoxic acid and to 5-hydroxy-6-methylcinchomeronic acid showed that 22% of the tritium was located in the 4-hydroxymethyl group and 21% in the 5-hydroxymethyl group. The isotope-retention curves of tritium and carbon 14 after administration of [3H8, 4, 5 – 14C2]pyridoxine to rats had approximately the same kinetic parameters, indicating that [3H8] pyridoxine may be used to calculate fractional turnover rates of vitamin B6. Two methods for the calculation of the body pool of vitamin B6 were evaluated and found to give comparable results, i.e. approx. 3 mg in rats weighing about 250 g.