590 IX. CAROTENOIDS AND VITAMINS A 



sible differences in the effectiveness of different forms of vitamin A have 

 produced conflicting results. Kagan and co-workers'-^ found no difference 

 in the effectiveness of vitamin A alcohol or ^'itamin A palmitate when given 

 in aqueous dispersion to normal children, irrespective of whether the free 

 alcohol or the palmitate was employed. On the other hand, Week and 

 Sevigne'^^ found that the liver storage of vitamin A in chickens after the 

 feeding of \dtamin A alcohol and vitamin A acetate was greater than when 

 the palmitate ester of the vitamin was employed, especially when the sol- 

 vent employed was jojoba oil. In a later study by these workers,''^ 

 similar results were obtained on human subjects when the test dose of \'ita- 

 min A was given in a vegetable margarine. Thus, vitamin A alcohol was 

 found to be superior in its ability to increase plasma vitamin A. as com- 

 pared with vitamin A acetate, which, in turn, gave better results than did 

 one natural vitamin A ester tested. However, this was not true in the case 

 of a second ester. On the other hand, Popper et al.^^^^ obtained opposite 

 results after the two forms of vitamin K were fed in aqueous dispersion or 

 in oily solution. The plasma vitamin A le\'el was slightly higher after the 

 intake of vitamin A esters than after the alcohol had been ingested. "\^ita- 

 min A in an aqueous medium resulted in a higher plasma level than did an 

 equal amount given in oil. The increase was mainly due to an increase in 

 \atamin A esters, regardless of whether the alcohol or the ester form had 

 been administered. Carotene has been reported, on the basis of growth 

 tests, to be better utilized when administered in margarine fat than when 

 given in other oils.^° 



e. Stress Factors. Ershoff'"'^ demonstrated that the vitamin A require- 

 ment in immature rats was augmented when they were maintained in a 

 cold environment (2°C.), as compared with a normal temperature (23°C.). 

 Thus, when rats were kept in the cold on a vitamin A-deficient diet, they 

 exhibited a more rapid depletion of vitamin A, and they survived for a 

 shorter period than did animals kept under similar conditions but at a higher 

 environmental temperature. 



The \atamin A requirements are likewise related to the acti\dty of the 

 thyroid gland. Thus, Greaves and Schmidt"" observed that thyroxine ac- 

 celerated the release of vitamin A from the livers of rats on a vitamin A- 

 free regimen; thyroxine was also sho^vTi to increase the vitamin A storage 

 of carotene in the liver, but not that of preformed vitamin A.^^ In the 

 case of cows and goats, Chanda and Owen^" noted that the administration 



loi" H. Popper, F. Steigmann, and H. A. Dyniew-icz, Proc. Soc. Exptl. Biol. Med., 73, 

 188-190(1950). 



i»i9 B. H. Ershoff, Proc. Soc. Exptl. Biol. Med., 74, 586-587 (1950). 



