NICOTINIC ACID (nIACIN) 



respect, nicotinic acid resembled aneurine, riboflavine and pyridoxine, 

 but differed from _/)-aminobenzoic acid, folic acid, biotin and panto- 

 thenic acid. Thus, intestinal synthesis is normally of less importance 

 in the first group, to which nicotinic acid belongs, than in the second. 

 On a restricted diet, the faecal excretion of nicotinic acid was as high 

 as on the normal diet and was unaffected by supplementation with the 

 vitamin, whereas the urinary excretion was reduced, and increased on 

 supplementation though not to the normal value. '^ On the restricted 

 diet the combined urinary and faecal output exceeded the intake. 



In none of these experiments does the intake of tryptophan appear 

 to have been controlled, so that variations in the output of N^-methyl- 

 nicotinamide and other metabolites may have been due to variations 

 in the amount of tryptophan in the diet. This factor alone, however, 

 would scarcely explain the effect of succinyl sulphathiazole on the 

 urinary excretion of N^-methylnicotinamide, and there appears to be 

 little doubt that nicotinic acid is synthesised by the intestinal flora 

 and can be utilised under certain conditions. It is to be hoped that 

 further investigations will indicate what these conditions are. 



S. W. Hardwick ^ noted that an acute nicotinic acid deficiency was 

 produced in a psychotic patient given sulphaguanidine for the treat- 

 ment of dysentery, thus providing further confirmation of the above 

 conclusions. 



A. C. Frazer,^" however, rejects the views held by Ellinger et al. 

 that in man nicotinic acid (and other vitamins) synthesised by intes- 

 tinal bacteria are normally absorbed. He suggests that in sprue, 

 with which a deficiency of nicotinic acid and other B vitamins is 

 frequently associated, bacterial synthesis is greatly enhanced, the 

 intestinal contents often being richer in certain vitamins than the 

 diet. He believes that the bacteria may invade areas of the small 

 intestine that are normally absorbing, and that here they compete 

 with the host for essential nutrients, thus giving rise to s3nnptoms of 

 vitamin deficiency. 



Intestinal Synthesis in Animals 



It is probable that in other species of animals, nicotinic acid is 

 synthesised by the intestinal flora, but evidence that nicotinic acid 

 produced in this way is utilised by animals is not conclusive. Thus, 

 lambs fed from the age of three to eight months on a diet producing 

 blacktongue in dogs, continued to excrete normal amounts of nico- 

 tinic acid,^ but it was not certain whether this was synthesised from 

 tryptophan in the tissues or derived from micro-organisms in the 

 rumen. Chicks appear to be capable of synthesising about one-sixth 

 of their nicotinic acid requirements.^^ 



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