384 THE BIOCHEMISTRY OF B VITAMINS 



the manner previously mentioned, however. It would thus appear that 

 the role of the B vitamins in the reproductive process per se is no more 

 than a composite of the various facets previously discussed: the increased 

 requirements (p. 269), the general metabolism, and the endocrine rela- 

 tionships. The clinical synthesis of these items is a problem beyond the 

 realm of this monograph. 



Nerve Function. The "special" functions of the B vitamins considered 

 in this section may be considered as "special" largely because they occur 

 in the higher animals and may not be considered in terms of the funda- 

 mental metabolism of a single cell. Thus endocrine relationships and the 

 metabolism of large aggregates of cells are considerations peculiar to 

 higher animals as contrasted to single cells. Nervous function is similarly 

 a specialized activity, and one in which several vitamins are particularly 

 involved in addition to their fundamental role in the life of the neuron. 

 From the standpoint of maintaining the lipoid myelin sheath and the 

 transfer of the nerve impulse along the nerve cell, special relationships 

 may well exist which can as yet only be surmised. For nerve impulse 

 transmission, in which acetylcholine is critically involved, thiamine and 

 pantothenic acid at least must play particularly important roles. 

 Coenzyme A is known to function in the acetylation of choline, and the 

 vital nature of this reaction would dictate a critical role in the metabolic 

 interchange in the neurone. 



Thiamine, by virtue of its role in the conversion of pyruvate to acetate, 

 is obviously important in the supplying of a constant source of acetyl 

 groups for the pantothenate-mediated coupling, thus: 



thiamine 



pyruvate >■ acetate") coenzyme A 



+ > — > acetylcholine 



choline/ 



It has been observed that diffusible thiamine is present in stimulated 

 nerves in four to eight times the concentration that it exists in resting 

 nerves, as measured by bradycardia tests and Phycomyces tests, but that 

 equal amounts are indicated by yeast fermentation tests. 40, 41 This excess 

 of diffusible thiamine disappears rapidly after stimulation, however. In 

 nerve poisoned with iodoacetate, by contrast, there is an apparent pre- 

 ponderance of diffusible thiamine in resting nerve. 42 Thiamine (but not 

 cocarboxylase) is said to block acetylcholine action upon the heart, more- 

 over. 43 The significance of these observations on the basis of the role of 

 thiamine proposed above is not too clear, and indeed Muralt has proposed 

 that thiamine must be considered not only as a catalyst, but also as a 

 metabolic substance in nerve biochemistry. 44 The justification for such 



