530 NIACIN 



by Hiindley^^ that the conversion of tryptophan to nicotinic acid proceeded 

 with normal efficiency in rats surgically deprived of their entire intestine. 



2. Synthesis by Intestinal Microorganisms 



These findings, however, do not necessarily mean that under normal 

 conditions the intestinal bacteria may not convert some tryptophan to 

 nicotinic acid or, in addition perhaps, synthesize some nicotinic acid from 

 other precursors which may be utilized by the host. The entire question 

 of intestinal synthesis of vitamins in relation to the vitamin economy of 

 the host is a complicated question which is very difficult to approach by 

 direct, conclusive experimentation. Some aspects of this question have 

 been reviewed in the section on requirements (p. 583). 



There is little direct evidence indicating how much influence intestinal 

 bacteria may have on the nicotinic acid requirement of the host by virtue 

 of the participation of such bacteria in the conversion of tryptophan to 

 nicotinic acid. There is little, if any, direct relationship between the nico- 

 tinic acid content of the cecum or of the feces and tryptophan in 

 the diet.^^' ^^- ^- Junqueira and Schweigert^^ found that sulfasuxidine, added 

 to rat diets for the purpose of suppressing intestinal microbial activity, 

 had no influence on the efficiency of conversion of tryptophan to nicotinic 

 acid. However, if the diets were deficient in folic acid, then sulfasuxidine 

 did reduce the amount of nicotinic acid formed from tryptophan. Further- 

 more, Ellinger and Abdel Kader^^- ^^ found that oral tryptophan was two 

 to five times as effective as parenteral tryptophan in increasing urinary 

 N'-methylnicotinamide whereas tryptophan given orally to rats receiving 

 sulfasuxidine produced little or no increase in N^-methylnicotinamide ex- 

 cretion. Other investigators have not found such a wide discrepancy be- 

 tween the relative effectiveness of oral and parenteral tryptophan. For 

 instance, Rosen et al.^^ found oral tryptophan about two times as effective 

 as parenteral tryptophan in increasing urinary nicotinic acid metabolites. 

 Snyderman et al.^^ found oral and parenteral tryptophan equally effective 

 in increasing urinary N^-methylnicotinamide in infants. Sung and Tung^^ 



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 92 M. Mason and C. P. Berg, J. Biol. Chem. 195, 515 (1952). 

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(1949). 

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 95 L. M. Henderson and L. V. Hankes, Proc. Sac. Exptl. Biol. Med. 70, 26 (1949). 

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