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Tissue B-6 Vitamer Concentrations in Rats Fed Excess Vitamin B-6^1,2,3,

Western Human Nutrition Research Center, U.S. Department of Agriculture, Agricultural Research Service, Presidio of San Francisco, CA 94129 ^* Biochemistry Department, Fort Wayne State Development Center, Fort Wayne, IN 46835

Diets containing 1, 10, 100, 175 or 250 times the NRC recommended level of pyridoxine HCl (7 mg/kg) were fed to rats (218 g, 12 per group) to evaluate the effects on tissue B-6 vitamer concentrations. After 10 wk, food intake and body weights did not differ among groups. Overt toxicity was not observed. Tissues were taken from five rats of each group after overnight food deprivation (unfed rats); the remaining seven rats in each group were allowed access to food (fed rats). In plasma of unfed rats, 4-pyridoxic acid and pyridoxal concentrations increased significantly (P < 0.05) with increasing dietary pyridoxine; pyridoxal phosphate was not affected by dietary pyridoxine. Concentrations of pyridoxal phosphate and pyridoxal increased significantly with increasing dietary pyridoxine in erythrocytes of unfed rats. Excretion of urinary B-6 vitamers and 4-pyridoxic acid in a 24-h period increased with dietary pyridoxine in fed rats. As dietary pyridoxine was increased, kidney pyridoxal concentrations increased significantly in fed rats only. Dietary pyridoxine did not affect vitamer concentration in muscle and liver of either unfed or fed rats, or in brain of unfed rats. Muscle glycogen phosphorylase, which contains pyridoxal phosphate, was not affected by dietary pyridoxine. There was a marginally significant (P = 0.058) increase in erythrocyte alanine, but not in aspartate, aminotransferase activity with increasing dietary pyridoxine. Plasma concentration of pyridoxal phosphate, which is used as a measure of vitamin B-6 status, did not reflect intake of pyridoxine in this study. Likewise, muscle pyridoxal phosphate and glycogen phosphorylase, advanced as possible reservoirs of vitamin B-6 because of positive correlations with dietary vitamin B-6 under some conditions, were unresponsive to excess dietary vitamin B-6.

KEY WORDS: • vitamin B-6 • tissues • HPLC • pyridioxine supplement • rats

¹ Presentation of food intake and body weight results from rats of this experiment at a different time point (wk 7) was made in Schaeffer, M. C. & Gallahger, J. (1991) Excess dietary vitamin B-6 alters acoustic startle behavior in rats. FASEB J. 5: A556 (abs. 1078) and in Schaeffer, M. C. (1993) Excess dietary vitamin B-6 alters startle behavior of rats. J. Nutr. 123: 1444-1452.

² Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of a product name by the USDA implies no approval of the product to the exclusion of others that may also be suitable.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

Manuscript received 7 November 1994. Revision accepted 8 March 1995.