128 CHOLINE 



it would appear that intestinal bacteria are responsible for the breakdown 

 observed. In rats about 40% of orally administered choline chloride is 

 excreted in the urine as trimethylamine or its oxide. ^^ 



XII. Requirements 



A. REQUIREMENTS OF ANIMALS 



WENDELL H. GRIFFITH and JOSEPH F. NYC 



Requirements of choline in the rat, chick, and turkey poult have been 

 stated for specific dietary conditions in the preceding discussion. Require- 

 ments cannot be described otherwise at the present time because of the 

 multiplicity of factors that govern the dietary need of this substance. 

 There is experimental support for the provisional conclusion that choline 

 is indispensable in the diet of chicks. This conclusion may need revision if 

 it is shown that mono- and dimethylaminoethanol can be methylated by 

 formate-to-methyl synthesis or by transmethylation at a rate sufficiently 

 rapid to meet the chick's demand for choline. In the event that such a 

 finding is established, the effect would be merely the transfer of dietary 

 indispensability from choline to monomethylaminoethanol. There is no 

 evidence of wide and ample distribution of the latter compound in natural 

 foods. In so far as the rat and other animal species are concerned, there 

 appears little cjuestion concerning the ability to produce methyl groups. 

 Whether or not the rate of formation by this means is ever adequate for 

 growth, reproduction and lactation on diets completely devoid of choline 

 but otherwise of reasonable composition remains to be determined. 



Among the dietary factors that influence the requirement of preformed 

 choline are (1) those that are involved in the enzymatic reactions of trans- 

 methylation and of formate-to-methyl synthesis, (2) those that provide 

 labile methyl, and (3) those that affect metabolism generally. In the first 

 category are folic acid and B12 without which the choline requirement is 

 definitely increased. In the second category are methyl donors other than 

 choline, such as methionine, betaine, and the thetins. Of these, only methio- 

 nine occurs widely in nature, and the quantity and composition of dietary 

 protein are, therefore, important factors in determining how much choline 

 should be contained in the ingested food. In the third category are any 

 modifications of the food mixture, including a decrease in the amount 

 consumed, that may lower the requirement of choline by depression of 



" H. Popper, J. de La Huerga, and D. Koch-Weser, /. Lah. Clin. Med. 39, 725-736 

 (1952). 



