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Laboratory of Nutrition, School of Nursing, National Yang-Ming University, Taipei, TAIWAN
Address reprint requests to: Ien-Lan Wei, PhD, Laboratory of Nutrition, School of Nursing, National Yang-Ming University, Taipei 112, TAIWAN
Objective: The purpose of this study was to assess the effect of dietary restriction on tissue distribution of vitamin B-6 vitamers and activities of vitamin B-6 metabolizing enzymes in rats.
Methods: Male rats were subjected to a 40% dietary restriction for 10, 20 or 40 weeks. The tissue vitamin B-6 vitamer concentrations and activities of the vitamin B-6 metabolizing enzymes of the animals were determined.
Results: The plasma pyridoxal 5'-phosphate (PLP) concentrations of the diet-restricted (DR) rats were comparable to those of the control group at week ten but were significantly lower at weeks 20 and 40. These significantly lower levels of plasma PLP in DR rats might in part be related to lower hepatic pyridoxal kinase and pyridoxamine (pyridoxine) 5'-phosphate oxidase activities. The urinary 4-pyridoxic acid excretion of the DR groups responded to the reduced food intake and were lower at weeks 10 and 20. Tissue levels of PLP were not affected by dietary restriction. In contrast, greater levels of pyridoxamine 5'-phosphate were found in liver, kidney and heart of the DR animals.
Conclusion: The duration of dietary restriction influenced the distribution of vitamin B-6 vitamers. When plasma PLP is used to evaluate vitamin B-6 status, the length of dietary restriction should be considered.
Key words: dietary restriction, vitamin B-6, tissues, rats
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