Absorption and metabolism of pyridoxamine in mice. II. Transformation of pyridoxamine to pyridoxal in intestinal tissues.

The absorption of pyridoxamine from the intestine of the mouse was studied in whole animals. [3H]Pyridoxamine was orally administered and the distribution of isotope between the six recognized forms of vitamin B6 was determined in portal blood after the administration. When small doses (1.4 or 14 nmol) were administered, labeled pyridoxamine could hardly be found in the portal blood, although labeled pyridoxal and pyridoxal phosphate were found in the same blood. However, when a large amount (46 or 140 nmol) was given, a significant amount of labeled pyridoxamine was found with labeled pyridoxal and pyridoxal phosphate in the portal blood. These results suggest that a physiological dose of pyridoxamine is rapidly transformed to pyridoxal in the intestinal tissues and then released in the form of pyridoxal into the portal blood.