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Role of Intestinal Microflora in the Metabolism of Vitamin B-6 and 4'-Deoxypyridoxine Examined Using Germfree Guinea Pigs and Rats^{1, 2,}

Stephen P. Coburn^*, J. Dennis Mahuren^*, Bernard S. Wostmann, David L. Snyder and Douglas W. Townsend

^* Biochemistry Department, Fort Wayne State Developmental Center, Fort Wayne, IN 46835, Department of Biological Sciences, Lobund Laboratory, University of Notre Dame, Notre Dame, IN 46556, Department of Mathematical Sciences, Indiana University-Purdue University, Fort Wayne, IN 46805

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. Labeling 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 germfree 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.

KEY WORDS: • vitamin B-6 • germfree • intestinal microflora

¹ Supported in part by grant 85-CRCR-1-1554 from the USDA Competitive Grant Program. ¹⁴C-Pyridoxine was donated by Hoffman-LaRoche Inc., Nutley, NJ.

² Presented in part at the Federation of American Societies for Experimental Biology, March 29–April 2, 1987, Washington, D.C. [Mahuren, J. D., Coburn, S. P., Wostmann, B. S., Snyder, D. L. & Townsend, D. W. (1987) Vitamin B-6 produced by intestinal synthesis is not utilized by rats receiving a nutritionally complete diet. Fed. Proc. 46: 1487 (abs.)].

Manuscript received 9 February 1988. Revision accepted 11 October 1988.