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The Metabolism of Small Doses of Vitamin B-6 in Men^1,2,3,

Department of Foods and Nutrition, Oregon State University, Corvallis, OR 97331

The metabolism of small doses of pyridoxine (PN) and of equimolar doses of PN, pyridoxal (PL) and pyridoxamine (PM) was studied in five men. Fasting subjects were given 0, 0.5, 1, 2, 4 and 10 mg pyridoxine HCl and 19.45 µmoles of PN, PM and PL; one dose was administered a week. Plasma total vitamin B-6 (B-6) and pyridoxal phosphate (PLP), and urinary B-6 and 4-pyridoxic acid (4PA) were determined in timed blood and urine samples collected after each dose. The PN doses had a significant (P < 0.01) overall effect on all of these measurements; the relationship between PN level and the subjects' responses was linear (P < 0.01). Plasma B-6 peaked at 0.5 or 1 hour after the PN doses; PLP at 0.5, 1 or 3 hours, depending on size of dose. Plasma B-6 but not PLP approached fasting levels 3 to 5 hours after the 0.5- to 4-mg PN doses; both plasma B-6 and PLP were still elevated 24 hours after 10 mg PN. In general, the rate of urinary B-6 and 4PA excretion was maximal the first 3 hours after the doses. With increasing PN doses, the percent of the dose recovered as urinary B-6 and 4PA decreased from 9 to 7% and 63 to 35%, respectively. Immediately following PL, plasma B-6 and urinary 4PA rose steeply indicating the rapid plasma clearance and oxidation of this B-6 vitamer. Responses to PM were generally slower than for PN or PL, suggesting that PM is absorbed more slowly or metabolized differently, or both, than PL or PN. A dose of at least 1 mg of B-6 is necessary to obtain measurable changes in vitamin B-6 metabolism.

KEY WORDS: • pyridoxine • pyridoxal • pyridoxamine • plasma pyridoxal phosphate • 4-pyridoxic acid • vitamin B-6 • humans

¹ Oregon Agricultural Experiment Station. Publication No. 5224.

² Supported in part by funds from Oregon Agricultural Experiment Station. This study is a part of the Western Regional Research Project W-143, Nutrient Bioavailability—A Key to Human Nutrition.

³ Preliminary results of this work has been presented: Wozenski, J. R., Leklem, J. E. & Miller, L. T. (1978) Metabolism of small doses of vitamin B-6 in men. Fed. Proc. 37, 449.

⁴ Present address: c/o Mwamufuja. 1PD-SCAP B. P. 4056 Douala, Cameroun.

⁵ To whom reprint requests should be sent.

Manuscript received 12 July 1979.

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