378 THE BIOCHEMISTRY OF B VITAMINS 



comes so disproportionate as to upset the usual functions and become 

 manifest, or they may at higher concentrations react in enzyme systems 

 in which they are normally alien, in the manner of analogue inhibitors 

 (Sect. D) . These considerations have not as yet been intensively investi- 

 gated, and there is little real knowledge in this regard. 



The study of the pharmacology and toxicology of the B vitamins is of 

 interest largely in that it throws light on two major problems: what the 

 effects of large doses or prolonged treatment with a given vitamin will 

 be, and to what extent the special physiological relationships to be con- 

 sidered here (and their derangement, considered in the next chapter) may 

 be related to the pharmacological activity of the vitamin. Most author- 

 ities now feel that there is little real relationship between the often ap- 

 parent similarity in physiological and pharmacological activities of the 

 B vitamins, being so decided largely by virtue of the thousandfold differ- 

 ence that generally exists between the two levels. Whether or not such 

 an opinion is justified, it is certainly true that the three levels of activity 

 of the B vitamins can be most adequately expressed in terms of micro- 

 grams, milligrams, and grams, respectively. In this regard, one of the 

 most distinctive and remarkable things about the B vitamin group is 

 certainly the high physiological activity per unit weight, coupled with the 

 low toxicity exhibited by these substances which, on the basis of struc- 

 tural considerations alone, might be predicted to be highly toxic. A 

 further reason for the consideration of certain pharmacological aspects 

 of the B vitamins lies in the aspect that the precise mode of action of 

 most drugs is as yet unknown. Present knowledge indicates, however, 

 that it will eventually be shown that most drugs, at least, exert their 

 action through specific enzyme systems. In view of the fact that so many 

 of these systems involve B vitamins as coenzymes, it may be surmised 

 that a growing field of interest will develop in B vitamin-drug interrela- 

 tionships. 



Physiological Relationships 



Many of the special physiological interrelationships of the B vitamins 

 are only discernible in the light of their derangement, and are therefore 

 almost of necessity discussed in the next chapter. Most of the others 

 seem to be associated with certain categories that have been established 

 by tradition in the field of physiology — metabolism, endocrine function 

 and reproduction, nervous function, and mental activity. It is apparent 

 that these terms have little real meaning from the standpoint of being 

 distinct functional entities: they are so interdependent as to be in prac- 

 tice inseparable. Nevertheless they do convey sufficient indications of 

 various aspects of physiology for the present purpose, and are therefore 



