Role of Intestinal Microflora in the Metabolism of Vitamin B-6 and 4′-Deoxypyridoxine Examined Using Germfree Guinea Pigs and Rats

Abstract

In previous work identification of urinary metabolites of 4'-deoxypyridoxine which had been oxidized in the 5'-position and long-term dilution of labeled urinary metabolites with unlabeled molecules suggested possible microbial contributions. In the current studies germfree guinea pigs were able to convert 4'-deoxypyridoxine to 4'-deoxy-5-pyridoxic acid demonstrating that the ability to oxidize the 5'-position is not restricted to microorganisms. Labelling curves for urinary pyridoxic acid in rats continuously fed [14C]pyridoxine since weaning were similar in conventional and germfree animals indicating that any vitamin B-6 synthesized in the intestinal tract was not readily absorbed and metabolized. Therefore, coprophagy did not make a detectable contribution to vitamin B-6 metabolism in rats receiving a nutritionally complete diet. The difficulty in achieving comparable labeling in adult animals is probably due to very slow turnover of portions of the vitamin B-6 pool and not to microbial production of vitamin B-6. The total pool calculated from the radioactivity in the germ-free rats averaged 16.2 +/- 0.8 nmol vitamin B-6 compounds/g body wt. Only 10% of the ingested label was recovered in the feces. In addition, only about 50% of the label excreted in the urine appeared as 4-pyridoxic acid in rats. These observations suggest that it may be difficult to quantitate the total urinary and fecal excretion of ingested vitamin B-6 without using tracers.