Vitamin B6 Group. XV. Urinary Excretion of Pyridoxal, Pyridoxamine, Pyridoxine, and 4-Pyridoxic Acid in Human Subjects.

Abstract

The known metabolic products of vit. B6-pyridoxal, pyridoxamine, pyridoxine and pyridoxic acid - were measured in normal human urine and in the urine of human subjects each fed 1 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 amts. of this product than did pyridoxine or pyridoxamine. No evidence could be obtained showing the conversion of pyridoxal or pyridoxamine to pyridoxine. When pyri-doxal or pyridoxine was fed, the chief form in which the vit. occurred in the urine was the form fed. However, when pyridoxamine was fed both pyridoxal and pyridoxamine were excreted in approx. equal amts. Ingestion of pyridoxine also greatly increased the amt. of pyridoxal and pyridoxamine excreted. The excretion of all products was very rapid. The largest amts. of each of the compounds were found in samples collected 2 and 5 hrs. after ingestion of the dose. The levels of pyridoxic acid returned to normal values after 12 hrs, while the vit. levels had returned to normal within 8 hrs. The amt. 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 vit. B6 occurs, these findings suggest that a large proportion of the vit. B6 was converted to products still unknown.