The metabolism of 3H-pyridoxine in rat liver and brain.

A study of the metabolism and distribution of 3H-pyridoxine in normal rat liver and brain was done in animals given small single doses of the labeled vitamin intraperitoneally. Liver and brain tissues were collected from 1 h to 14 days. Perchloric acid extracts of tissues were fractionated by an ion exchange chromatographic procedure and six B6 vitamers were separated and assayed for radioactivity and microbiological activity. In liver 3H-pyridoxal phosphate peaked at 1 h after the administration of 3H-pyridoxine; however, the accumulation of total isotope in combined vitamers continued slowly until 4 h. During the first 4 h, about 50% of the tritium resided in the supernatant fraction of liver. In the brain, tritium accumulated slowly and reached a peak at day 7. Nearly 90% of the vitamin in the brain was in the form of pyridoxal phosphate and pyridoxamine phosphate. The concentrations of the total microbiologically active vitamin in the liver and brain were 35 to 40 and 20 to 25 nmol/g, respectively. However, the maximum amount of tritium in the brain was less than 10% of that in the liver. These data indicate that uptake and turnover of vitamin B6 in brain studied with tracer doses was very much slower than previously reported from studies with larger doses.