NICOTINIC ACID (NIACIN) 



clinicians for years, that milk and milk products, which are notoriously 

 poor in nicotinic acid, are, nevertheless, amongst the most valuable of 

 pellagra-preventive foodstuffs. Casein, the protein of milk, is a very 

 good source of tryptophan and it is this that prevents nicotinic acid 

 deficiency. 



The observation that tryptophan increased the growth rate of 

 rats fed on a diet containing corn grits was confirmed by H. Spector 

 and H. H. Mitchell. ^° Subsequent work indicated ^^ that administra- 

 tion of tryptophan led to the synthesis of nicotinic acid, which in turn 

 led to an improved utilisation of nicotinic acid. Moreover, Krehl et 

 al.^"^ found that the growth of rats was not inhibited by indole-3- 

 acetic acid or by cyanopyridine, indole or anthranilic acid, although 

 pyridine-3-sulphonic acid (see page 291) suppressed growth. From 

 this it would seem that the absence of both nicotinic acid and trypto- 

 phan from maize is a satisfactory explanation of its pellagragenic 

 effect, and that it is unnecessary to postulate the existence of a toxic 

 factor in maize ; nor is the evidence for the existence of such a factor 

 particularly strong. Symptoms of nicotinic acid deficiency were 

 produced in pigs fed a diet containing a large proportion of maize, ^^ 

 and the symptoms were cured by the addition of tryptophan to the diet, 

 or by replacing the maize by oats. 



It has been demonstrated ^^"^^ that the pig, horse, cotton-rat, 

 chick, chick embryo and turkey, as well as the rat, are able to convert 

 dietary tryptophan into nicotinic acid, which is excreted either as the 

 free acid or as N^-methylnicotinamide (page 261). The mechanism 

 of the transformation in animals is discussed below (page 249). 



Symptoms of Pellagra 



The symptoms exhibited in pellagra and in " pseudo-pellagrous 

 conditions " (page 244) depend on whether or not the nicotinic acid 

 deficiency is accompanied by a deficiency of other members of the 

 vitamin B complex, and on the speed with which the body reserves 

 are depleted. A chronic partial deficiency produces functional and 

 anatomical changes quite different from those produced by an acute 

 or total depletion of the vitamin reserves.^'^ A partial deficiency, for 

 instance, may produce mild biochemical disturbances, which in course 

 of time may lead to irreversible anatomical changes, whereas a gross 

 deficiency may cause severe functional disturbances, sometimes fatal, 

 often without any gross anatomical lesions developing. 



In classical pellagra, alcoholic pellagra and other pseudo-pellagrous 

 states, psychic disturbances generally precede other manifestations by 

 weeks or months. The usual symptoms are lassitude, slight mental 

 retardation, loss of memory for recent events, apprehension and a 



242 



