METABOLISM 



12. J. R. Maxfield. A. J. Mcllwain and J. E. Robertson, Radiology, 



1943. 41, 383. 



13. S. G. Smith and D. W. Martin, Proc. Sac. Exp. Biol. Med., 1940, 



43, 660. 



14. N. JollifEe, L. A. Rosenbaum and J. Sawhill, /. Invest. Derm., 



1942, 6, 143- 



15. M. M. Cantor and J. W. Scott, Canad. Med. Assoc. J., 1945, 62, 



368 ; Fed. Proc, 1945, 4, 85. 



16. E. H. Fishberg and J. Forzimer, Proc. Soc. Exp. Biol. Med., 1945, 



60, 181. 



II. 2VIETABOLISM OF PYRIDOXINE 



The metabolism of pyridoxine was first studied by Scudi and his 

 co-workers. Using the reaction with 2 : 6-dichloroquinone chloro- 

 imide, they showed ^ that at levels of 10 mg. per kg. or over, normal 

 or vitamin Bg-deficient rats excreted 50 to 70 % of a test dose but, 

 at lower levels, normal rats excreted a higher proportion of the test 

 dose than did vitamin Bg-deficient animals. Dogs excreted only 

 20 % of a 25- to 500-mg. dose of pyridoxine within one to six hours 

 of oral administration, and humans only 87 % of a 50-mg. test dose 

 given intravenously one hour previously, or 7-6 % of a loo-mg. dose 

 given orally four hours previously.^ 



In humans, the excretion of pyridoxine apparently varied with 

 the age of the subject, ^ most patients under fifty years of age ex- 

 creting 8-4 % of a 50-mg. test dose and most patients over fifty ex- 

 creting 7-2 % and a few as little as 2-3 % ; these were mostly chronic 

 renal cases. Patients from five to fifteen years of age excreted an 

 average of 21-3 %. The excretion of 8-o % and 8-4 % of a test dose 

 by adults was regarded by Spies et at.* and by J. Flexner and M. R. 

 Chassin ^ respectively as indicating a normal level of nutrition. 



M. Swaminathan ^ stated that the daily excretion of pyridoxine 

 in man was 400 to 560 [ig. and that about 5 % of a 50-mg. test dose 

 was excreted by normal (Indian) adults. He also reported that ^ 

 rats receiving 0-9 )u,g. of pyridoxine per day excreted i-o /xg. per day 

 in excess of the intake, whereas rats receiving 10 /xg. per day excreted 

 37 /xg. The vitamin Bg content of the liver and muscle was lower 

 on the unsupplemented than on the supplemented diet and the excess 

 vitamin may have been derived from these tissues. 



Unfortunately, the inferences drawn from these early results on 

 the excretion of pyridoxine by animals and humans were vitiated by 

 the subsequent discovery that pyridoxine was converted in vivo into 

 other substances, which were excreted in the urine along with un- 

 changed pyridoxine. These metabolites represented a large proportion 



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