PYRIDOXINE 



Denko et al.,^ who reported that the faecal excretion was as high on a 

 restricted intake of pyridoxine as on a normal diet. Furthermore, 

 the faecal excretion was unaffected when the diet was supplemented 

 by additional pyridoxine. The urinary excretion, on the other hand, 

 fell moderately on the restricted diet, and returned to normal on 

 supplementation. On all diets, the amount of pyridoxine excreted in 

 the urine was greater than the amount excreted in the faeces, and the 

 total excretion was less than the dietary intake. Thus, there is clear 

 evidence that pyridoxine is synthesised in the intestine, but not that 

 it is utilised in man. In this respect, pyridoxine falls into the group 

 of B vitamins that includes aneurine, riboflavine and nicotinic acid, 

 rather than into the group that includes biotin and folic acid, where 

 there is a strong presumption that both synthesis and utilisation occur. 

 Pyridoxine is undoubtedly synthesised by ruminants, and L. W. 

 McElroy and H. Goss * found that dried sheep rumen and reticulum 

 contained lo /u.g. of pyridoxine per g. and the rumen contents of a 

 fistulated cow 8 /xg. per g. In each instance, the ration contained 

 only I to 1-5 /xg. of pyridoxine per g. The cow supplied milk with 

 the normal pyridoxine content in spite of the fistula. 



References to Section 12 



1. H. Chick, T. F. Macrae and A. N. Worden, Biochem. J., 1940, 34, 580. 



2. P. S. Sarma, E. E. Snell and C. A. Elvehjem, /. Biol. Chem., 1946, 



165. 55. 

 2a. K. J. Carpenter, L. J. Harris and E. Kodicek, Brit. J. Nutrition, 

 1948, 2, vii. 



3. C. W. Denko, W. A. Grundy, J. W. Porter, G. H. Berryman, T. E. 



Friedemann and J. B. Youmans, Arch. Biochem., 1946, 10, 33 ; 

 C. W. Denko, W. E. Grundy, N. C. Wheeler, C. R. Henderson, 

 G. H. Berryman, T. E. Friedemann and J. B. Youmans, ibid. 

 1946, 11, 109. 



4. L. W. McElroy and H. Goss, /. Nutrition, 1940, 20, 527. 



13. ANIMAL AND HUMAN REQUIREMENTS OF PYRIDOXINE 



Considerable uncertainty exists concerning the requirements of 

 animals and man for pyridoxine, not so much because of the possi- 

 bility that pyridoxine may be synthesised by intestinal bacteria, but 

 rather because vitamin Bg has a three-fold function (page 330), one 

 of which may conceivably be more readily put out of action than the 

 others by a sub-optimal intake of pyridoxine. In that event the 

 level of pyridoxine necessary to enable one type of function to be 

 carried on would be higher than the level necessary for another 

 function to be maintained. Then, too, in attempting to assess 



328 



