450 IX. CAROTENOIDS AND VITAMINS A 



was active in the case of aureomycin, it was concluded that the two antibi- 

 otics have different effects. -^"^ 



Vitamin E (a-tocopheryl acetate) and certain fat-soluble antioxidants 

 related to hydroquinone were found by High et al.-^^ to depress the conver- 

 sion of carotene to vitamin A in rats. However, Almquist and Maurer^^" 

 were unable to show that the antioxidant DPPD (A'',A/''-diphenyl-p- 

 phenylenediamine) exerted any effect upon the conversion of carotene to 

 vitamin A. Herbert and Morgan^^^ found that the addition of 0.5 or 1.0 

 mg. of a-tocopherol daily to the diet of rats fed on diets containing generous 

 amounts of vitamin A or carotene consistently failed to augment the 

 storage of vitamin A in the liver to any great extent. 



Octachloronaphthalene (OCN), which is a widely used insecticide, mark- 

 edly decreased the storage of vitamin A in the liver. -^^ Thus, a progressive 

 decrease in the liver vitamin A of rats was found with diets containing 0, 

 0.05, 0.2, and 0.5% of OCN, namely 37.6, 13.9, 8.4, and 4.6 fig./g., respec- 

 tively. When |(3-carotene was employed as the source of vitamin A, no 

 difference in liver vitamin A was observed after the provitamin had been 

 injected intravenously in aqueous solution, whether or not OCN was 

 included in the diet. However, when carotene was given orally, the drug 

 apparently decreased vitamin A storage. 



Rosenberg and SobeP^^ demonstrated that the amount of hepatic stores 

 of vitamin A originatmg after a standard dose of /3-carotene was much less 

 in rats suffering from alloxan diabetes than in normal controls. It is 

 believed that this phenomenon obtains because alloxan depresses the con- 

 version of carotene to vitamin A. 



(2) The Ester ification of Vitamin A 



It is generally agreed that an enzyme exists in the intestinal wall which 

 functions in the esterification of vitamin A. This hypothesis is supported 

 by the fact that the vitamin A present in the chyle of the rat and pig 

 appears to a considerable extent in the form of vitamin A ester, irrespective 

 of whether its source was ingested vitamin A alcohol, vitamin A ester, or 

 one of the provitamins A. Thompson et al}^^ observed that about 50% of 

 the vitamin A in the intestinal wall was in the form of its ester when it 



"6 E. G. High, H. C. Smith, Jr., H. H. Taylor, and S. S. Wilson, /. Biol. Chem., 210, 

 681-686 (1954). 



21" J. W. Herbert and A. F. Morgan, J. Nutrition, 50, 175-190 (1953). 



217 J. G. Bieri and R. J. Edwards, Federation Proc, 14, 428 (1955). 



218 A. Rosenberg and A. E. Sobel, Arch. Biochem. Biophys., U, 326-329 (1953). 



