Absorption and metabolism of pyridoxamine in mice. I. Pyridoxal as the only form of transport in blood.

[3H]Pyridoxamine was orally administered to mice in physiological amounts, and the distribution of isotope between the six recognized forms of vitamin B6 and pyridoxic acid was determined at different times in the intestine, liver, blood, and brain. After 7 min about 50% of the radioactivity in pyridoxamine had been absorbed by the intestine and transported to the blood and other organs. Labeled pyridoxal phosphate was found in the intestine and liver. Labeled pyridoxamine could not be detected in the peripheral blood, but substantial amounts of labeled pyridoxal and pyridoxal phosphate were found in the blood. However, when a large amount (40-140 nmol) was given, a significant amount of labeled pyridoxamine was found in the blood, together with labeled pyridoxal and pyridoxal phosphate. These results suggest that the intestine and/or liver play a major role in completely converting physiological amounts of pyridoxamine to circulating pyridoxal, which is then taken up and phosphorylated by other organs.