Vitamin B 6 Group. XV. Urinary Excretion of Pyridoxal,Pyridoxamine,Pyridoxine,and 4-Pyridoxic Acid in Human Subjects. *

Abstract

Summary

The known metabolic products of vitamin B₆—pyridoxal, pyridoxamine, pyridoxine and pyridoxic acid—were measured in normal human urine and in the urine of human subjects each fed one of the 3 forms of the vitamin.

The chief product found, regardless of the form fed, was pyridoxic acid. Pyridoxal gave rise to significantly higher amounts of this product than did pyridoxine or pyridoxamine. No evidence could be obtained showing the conversion of pyridoxal or pyridoxamine to pyridoxine. When pyridoxal or pyridoxine was fed, the chief form in which the vitamin oc- curred in the urine was the form fed. However, when pyridoxamine was fed both pyridoxal and pyridoxamine were excreted in approximately equal amounts. Ingestion of pyridoxine also greatly increased the amount of pyridoxal and pyridoxamine excreted.

The excretion of all products was very rapid. The largest amounts of each of the compounds were found in samples collected 2 and 5 hours after ingestion of the dose. The levels of pyridoxic acid returned to normal values after 12 hours, while the vitamin levels had returned to normal within 8 hours. The amount of the dose recovered varied with the form fed. The highest recovery, 70%, was obtained when pyridoxal was fed; 45% of the pyridoxine was recovered, while only 31% of the pyridoxamine could be recovered. Together with published data which indicate that complete absorption of large doses of vitamin B₆ occurs, these findings suggest that a large proportion of the vitamin B₆ was converted to products still unknown.