Metabolism of Tritium- and ¹⁴C-Labeled Pyridoxine in the Rat

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.

Key Words:

• Metabolism
• [³H₈] pyridoxine
• [4, 5 – ¹⁴C₂] pyridoxine
• vitamin B₆