METABOLISM 



Only traces of nicotinamide and no nicotinic acid were excreted 

 in the sweat. '^^ 



The amounts of nicotinic acid and its derivatives in certain tissues 

 showed considerable variation according to the degree of nicotinic acid 

 deficiency. Thus in the rat, dog and pig, the amount of total nico- 

 tinic acid and coenzyme I in the liver and muscles decreased 

 progressively when the animals were maintained on a pellagra- 

 producing diet, but the amounts in the brain and kidney cortex, as 

 well as in the blood, showed little change. ^^' '^ Similarly, the coenzyme 

 I content of striated muscle was higher in normal human tissue (382 

 /zg. per g.) than in tissue from pellagrins (214 fjig. per g.^^) and the 

 administration of nicotinic acid led to a marked increase in the co- 

 enzyme I content. 



In normal dogs 50 % of the nicotinic acid in the liver and 25 % 

 of that in the muscle was present in the free state ; all the nicotinic 

 acid in the kidney cortex, on the other hand, was combined. '^^ 



The decrease in the tissue nicotinic acid of dogs with blacktongue 

 was almost entirely due to a fall in the bound nicotinic acid. Rabbits 

 also suffered a decrease in the amount of nicotinic acid present in the 

 voluntary muscles when fed for three months on a nicotinic acid- 

 deficient diet.'^^ 



Rats behaved differently from other species of animals. They 

 showed no increase in the coenzyme I content of the muscle tissues 

 when fed large amounts of nicotinic acid ; ^^ and the coenzyme I 

 contents of the liver, kidney and thigh muscle fell by only 10 % when 

 rats were maintained on a diet that produced blacktongue in dogs.^^ 

 This is due to the fact that rats synthesise nicotinic acid, and are 

 therefore independent of an external source of supply, provided 

 adequate tryptophan is present in the diet (page 241). All the nico- 

 tinic acid in the muscle and kidneys of rats was present as coenzyme, 

 but only 58 % of that in the liver was in the combined form.®^ 



Eggs contained 80 fig. of nicotinic acid, a value that remained 

 unchanged for eleven days, but increased to 470 /xg. after sixteen days 

 and to 820 /xg. on hatching. ^^ Most of the nicotinic acid was present 

 as diphosphopyridine nucleotide.®^ 



References to Section 10 



1. H. von Euler and F. Schlenk, Klin. Woch., 1939, 18, 1109. 



2. D. Melnick, W. D. Robinson and H. Field, /. Biol. Chem., 1940, 



136, 131, 145. 



3. W. W. Ktihnau, Klin. Woch., 1939, 18, 1333. 



4. D. Melnick and H. Field, /. Biol. Chem., 1940, 134, i ; 1940, 135, 



53. 



5. J. W. Huff and W. A. Perlzweig, /. Biol. Chem., 1941, 142, 401. 



265 



