REQUIREMENTS OF ANIMALS 591 



of thyroxine increased the vitamin A content of the milk when carotene- 

 containing diets were given. On the other hand, when no carotene was 

 present in the feed, the administration of thyroxine increased the propor- 

 tion of vitamin A alcohol in the milk, due to the mobilization of hepatic re- 

 serves. One must interpret these data as indicating that thyroxine in- 

 creases the vitaiTiin A requirement when the source of the vitamin is vita- 

 min A itself; when the source of vitamin A is the provitamin A, carotene, 

 thyroxine may not adversely affect vitamin A requirements, since the in- 

 creased excretion of the vitamin is partially compensated by a more effi- 

 cient transformation of carotene to vitamin A. 



f. Dietary Components Fed Simultaneously, (a) Tocopherols. In 1940, 

 Moore*'^^ called attention to the fact that the utilization of vitamin A as 

 denoted by liver storage was dependent upon vitamin E intake. More re- 

 cently, Moore and Sharman*^^^ demonstrated that the vitamin A storage in 

 the livers of female rats receiving 1,000 LIT. weekly did not reach the op- 

 timum level until 1 to 3 mg. of UL-a-tocopherol was given weekly. On 

 the other hand, Herbert and Morgan^^^ were unable to demonstrate any aug- 

 mentator}^ effect of 0.5 mg. per day of a-tocopherol on the liver storage of 

 vitamin A in partially vitamin A-depleted rats receiving 35 to 129 /xg. of 

 vitamin A daily, although an mcreased storage was noted in rats receiving 

 comparable doses of /^-carotene (24 to 174 /^g. daily) when 0.5 mg. of a- 

 tocopherol per day was gi\'en. The sparing effect of the tocopherols on 

 vitamin A was also sho\Mi by Hickman et a/.,'"" by means of growth rate 

 and survival studies. Furthermore, it was found that the tocopherols ex- 

 ert a sjmergistic effect upon growth after the administration of small and 

 moderate doses of the provitamin A.^°^ Hickman and co-workers ^''^'' 

 obser\'ed that a-, ^-, and 7-tocopherols are equally effective in sparing vita- 

 min A. 



Tocopherols exhibit a similar sparing action upon vitamin A in the case of 

 chickens. Dam ct a/.^'^^^ reported increased growth and a greater storage of 

 \'itamin A in the liver when synthetic tocopherol was added to a diet con- 

 taining 10% of cod liver oil, free tocopherol was found to be more effective 

 than esterified tocopherol. It was recorded that methylene blue, thiodi- 

 phenylamine, and Antabuse exhibited a similar behaAaor toward vitamin 

 A. However, the effect of the tocopherol was not noted in chickens when 

 this vitamin was added to a fat-free diet or to one containing lard. 



">2« K. C. D. Hickman, M. W. Kaley, and P. L. Harris, J. Biol. Chem., 152, 321-328 

 (1944). 



"•21 H. Uam, I. Prange, and E. S0ndergaard, Acta Pharmacol, et Toxicol., 8. 1-22 

 (1952). 



