Transport and metabolism of pyridoxine and pyridoxal in mice.

[3H]Pyridoxine or [3H]pyridoxal in physiological amounts was orally administered to mice and the distribution of isotope between the six recognized forms of vitamin B6 and pyridoxic acid was determined at different times after the administration in the intestine, liver, blood, and brain. After 7 min about 50% of the radioactivity in pyridoxine and pyridoxal had been absorbed by the intestine and transported to the blood and other organs. When [3H]pyridoxine was administered, labeled pyridoxal, pyridoxal- and pyridoxine-phosphate were found in the intestine and liver, and labeled pyridoxine could not be detected in the peripheral blood but substantial amounts of labeled pyridoxal and pyridoxal-phosphate were found in the blood. The time course of the blood [3H]pyridoxal levels following the administration of [3H]pyridoxine was similar to that following the administration of [3H]pyridoxal. These results suggest that the intestine and/or liver play a major role in converting dietary pyridoxine to circulating pyridoxal which is taken up and phosphorylated by other organs. Moreover, most of the blood [3H]pyridoxal was shown to be located in the plasma. This localization may facilitate utilization by the organs.