NICOTINIC ACID (nIACIN) 



Similarly when 6 g. of DL-tryptophan were fed to horses, the 

 amount of free nicotinic acid excreted increased two- to four-fold, 

 whereas the N^-methylnicotinamide remained unchanged.*^ This was 

 in marked contrast to the behaviour of cotton-rats, which excreted 

 large amounts of N^-methylnicotinamide after ingestion of nicotinic 

 acid or tryptophan. 



The amount of nicotinic acid formed from dietary tryptophan 

 was increased when pyridoxine was added to the diet of rats or mice, 

 a result to be anticipated from the fact that administration of trypto- 

 phan accentuated pyridoxine deficiency in the rat and mouse (see 

 pa-ge 331). Thus, when 100 mg. of DL-tryptophan were added to 

 the basal ration, rats fed pyridoxine excreted 8ro to 2190 fxg. of 

 N^-methylnicotinamide per day, whilst deficient animals excreted 

 180 to 485 fig. per day. ^3 With the basal diet only, the excretions 

 were 95 to 185 and 45 to 140 /xg. per day respectively. The corre- 

 sponding values for excreted nicotinic acid were 95 to 430 ; 16 to 35 ; 

 23 to 50 ; and 10 to 24 fig. per day. 



Conversely, when pyridoxine was omitted from the diet of rats 

 the amount of excreted nicotinic acid and metabolites fell. A similar 

 result was obtained when aneurine or riboflavine, but not pantothenic 

 acid or pteroylglutamic acid, were omitted. When sulphasuxidine 

 was added to a pteroylglutamic acid-deficient diet, however, nicotinic 

 acid excretion was depressed, although administration of sulphasuxi- 

 dine when the diet contained pteroylglutamic acid did not affect the 

 excretion. ^3" 



Nicotinic Acid in Blood and Cerebrospinal Fluid 



Some of the difficulties inherent in the estimation of nicotinic acid 

 in urine apply to its estimation in blood. 



Factor V 



The earliest values for the nicotinic acid content of blood relate to 

 its coenzyme, or as it was first called, " factor V ", content (see page 

 229). According to H. von Euler and F. Schlenk,^* normal blood 

 contained 4 to 8 mg. of factor V per 100 ml., and 150 jug. of nicotinamide 

 per 100 ml. 



The effect of nicotinic acid deficiency on the amount of coenzyme 

 present in various tissues of the dog was studied by Kohn et al.^^ and 

 by M. Pittman and H. F. Fraser,^^ who used Haemophilus para- 

 infliienzae as the test organism. They observed a decrease in the 

 factor V content of the liver and muscle in blacktongue, whilst Axelrod 

 et al.^"^ using a yeast fermentation method, found a similar decrease 



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