https://www.translationalres.com/article/0022-2143(85)90045-9/abstract

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Volume 106, Issue 5 | p491-497 | November 1985

Relationship between body store of vitamin B6 and plasma pyridoxal-P clearance: Metabolic balance studies in humansAlec Lui∙ Lawrence Lumeng ∙ George R. Aronoff ∙ Ting-Kai Li
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Article Info
Received December 11, 1984; Accepted July 9, 1985

Supported by the VA Medical Research Funds and the Public Health Service, General Clinical Research Center, Grant 5-MO-1-RR- 00750-12.

Presented in part at the Banff Conference on Vitamin B6 Nutrition and Metabolism, Oct. 8 to 10, 1984, Banff Centre, Alberta, Canada.

AbstractFactors that regulate the clearance of plasma pyridoxal-P (PLP) are unknown. Four volunteers were given a diet supplying ~12 μmol pyridoxine (PN) per day. The pharmacokinetics of plasma PLP clearance were measured in these subjects before and after 4 weeks of intravenous PN supplementation (122 μmol/day). Urinary B6 excretion, mainly as 4-pyridoxic acid (4-PA), increased progressively after initiation of PN supplementation until a new steady state was reached on day 10 of supplementation, whereupon >93% of the daily injected PN could be recovered in the urine. Hence, urinary excretion is almost the sole route for vitamin B6 elimination. Fasting plasma PLP concentration increased with supplementation and also reached a new steady state at this time. When supplementation was terminated, urinary B6 excretion decreased in 5 days to an amount only slightly higher than that before supplementation. This amount was maintained for 2 months. By comparison, plasma PLP decreased more slowly and remained considerably higher than the presupplementation level for the rest of the study. These data confirm that urinary 4-PA excretion is a better indicator of B6 intake than is plasma PLP content, whereas plasma PLP content is a better indicator of the body store of the vitamin. Plasma clearance and volume of distribution of PLP decreased significantly after supplementation, but half-life t12 did not change. Plasma clearance of PLP, therefore, is dependent on the vitamin B6 status of an individual.

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