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Influence of Age and Sex on Vitamin B-6 Vitamer Distribution and on Vitamin B-6 Metabolizing Enzymes in Wistar Rats¹

TNO-CIVO Toxicology and Nutrition Institute Zeist, Department of Clinical Biochemistry, 3700 AJ Zeist, The Netherlands

Vitamin B-6 vitamer distribution and activities of vitamin B-6 metabolizing enzymes were evaluated in aging male and female Wistar rats fed a purified diet (containing 250 g of casein and 6 mg of pyridoxine hydrochloride per kg) from weaning until 31 mo of age. Plasma pyridoxal 5'-phosphate (PLP) concentration became lower with increasing age, with the largest decrease in the 1st yr of life. An age-related change in vitamin B-6 distribution between the various tissues examined was observed: B-6 vitamer content increased in heart and brain, whereas PLP content decreased in gastrocnemius muscle, kidney and liver. The decrease in muscle PLP content occurred in concert with a decrease in muscle glycogen phosphorylase activity. Urinary 4-pyridoxic acid (4-PA) excretion increased with age, especially in female rats, in parallel with an increase in liver pyridoxal oxidase and pyridoxal dehydrogenase activities. Age-related changes in vitamin B-6 distribution were probably not causally related to changes in activity of vitamin B-6 metabolizing enzymes; they were regarded as consequences of changes in protein metabolism. The higher urinary 4-PA excretion in older rats may reflect a lower vitamin B-6 requirement; however, the lower PLP content of gastrocnemius muscle may indicate an age-related decrease in vitamin B-6 body stores.

KEY WORDS: • vitamin B-6 • aging • metabolism • distribution • rats

¹ Parts of the results were presented at The New York Academy of Sciences International Multidisciplinary Conference on Vitamin B-6, Philadelphia, PA, April 10–12, 1989. [Berg, H. van den, Bode, W., Mocking, J.A.J. & Löwik, M.R.H. (1990) Effect of aging on vitamin B-6 metabolism. Ann. N.Y. Acad. Sci. 585: 96–105].

² To whom correspondence should be addressed.

Manuscript received 3 May 1990. Revision accepted 21 August 1990.