IV. BIOCHEMICAL SYSTEMS 423 



to vitamin Bi2.''"'^ However, Ershoff^" reported that liver residue contained 

 a factor other than vitamin B12 which completely counteracted the growth- 

 retardinfi; cfTect of desiccated thyroid on rats fed purified diets containing 

 casein as the source of protein and sucrose as the soiu'ce of carbohydrate. 



Evidently, the requirement for vitamin B12 in rats, mice, and chicks is 

 increased by addin*!; thyroid to the diet. The mechanism of this interaction 

 is unknown. In addition, the hyperthyroidism induced on certain diets 

 may be counteracted by an unidentified factor in liver residue. Recent work 

 by Ershoff indicated-^ that soybean flour, kidney, and crude aureomycin 

 mash could replace the liver residue. 



It w'as suggested by Rupp and cow^orkers" that increased food intake 

 might partly account for the beneficial effects of vitamin B12 on hyper- 

 thyroid animals, and these investigators studied this point with groups of 

 "force-fed" rats. Their results indicated that vitamin B12 could decrease 

 the loss of nitrogen resulting from the catabolic action of thyroxine in 

 force-fed rats on constant food intake. 



A sex difference in the response of hyperthyroid rats to vitamin B12 was 

 noted by Bolene et al.,-^ who also found that maximum responses were not 

 obtained unless various crude materials were added to the diet. Further 

 studies-'* gave some indication that vitamin B12 was less effective than a 

 crude liver fraction for normal males and ovariectomized females, but the 

 two supplements produced the same response when fed to castrated males 

 and normal females. 



C. VITAMIN B12 AND LIVER FUNCTION 



The relation of vitamin B12 and folic acid to the metabolism of choline 

 and methionine (pp. 432 to 443) raised the possibility that these vitamins 

 might be shown to be involved in the prevention of fatty livers in rats, 



i*D. K. Bosshardt, W. J. Paul, K. O'Doherty, J. W. Huff, and R. H. Barnes, J. 



Nutrition 37, 21 (1949). 

 16 D. V. Frost, H. H. Fricke, and H. C. Spruth, Proc. Soc. Exptl. Biol. Med. 72, 102 



(1949). 

 " J. J. Betheil and H. A. Lardy, J. Nutrition 37, 495 (1949). 

 >8 U. D. Register, V. J. Lewis, and C. A. Elvehjem, Proc. Soc. Exptl. Biol. Med. 70, 



167 (1949). 

 19 G. A. Emerson, Proc. Soc. Exptl. Biol. Med. 70, 392 (1949). 

 " B. H. Ershoff, Arch. Biochem. 28, 359 (1950). 

 *• B. H. Ershoff, Paper presented at Nutrition Symposium, Yale University, Nov. 



10, 1950. 

 " J. Rupp, K. E. Pashkis, and A. Cantarow, Proc. Soc. Exptl. Biol. Med. 76, 432 



(1951). 

 23 C. Bolene, O. B. Ross, and R. Mac Vicar, Proc. Soc. Exptl. Biol. Med. 75, 610 (1950). 

 " A. B. Watts, O. B. Ross, C. K. Whitehair, and R. MacVicar, Proc. Soc. Exptl. 



Biol. Med. 77, 624 (1951). 



