DIGESTION, ETC. OF CAROTENOIDS IN THE G.I. TRACT 291 



(V) The Effect of Tocopherols. — The tocopherols are known to en- 

 hance the vitamin A effect of both carotene and vitamin A. 280 This 

 effect is probably to be traced to a protective action on the part of to- 

 copherol against oxidative destruction of provitamin A or vitamin A in the 

 gastrointestinal tract and at the site of utilization within the organism, 

 rather than to an effect on absorption. However, Major and Watts 281 

 were unable to demonstrate any improvement in the utilization of caro- 

 tene, or any increased deposition of vitamin A in the livers of rabbits on 

 high tocopherol diets as compared with results obtained with regimens 

 low in this vitamin. 



On the other hand, Swick and Baumann 282 demonstrated that high 

 doses of a-tocopherol, 7-tocopherol, and a-tocopherol acetate diminish 

 the storage of vitamin A in rats fed moderate doses of /3-carotene. 7- 

 Tocopherol was found to be nearly equal to a-tocopherol in inhibiting 

 vitamin A deposition under these conditions, while a-tocopherol acetate 

 was somewhat more active than the free vitamin E. Hydroquinone, 

 vitamin C, and diamylhydroquinone failed to increase the activity of a- 

 tocopherol, but diamylhydroquinone slightly reduced the deposition of 

 vitamin A. 



(c') The Effect of Xanthophylls. — The question as to whether or not 

 the xanthophylls increase or decrease the utilization of /3-carotene is still 

 uncertain. Sherman, 283 in 1947, reported that the addition of xanthophyll 

 to the diet of rats apparently decreased the destruction of carotene, vita- 

 min A alcohol, and vitamin A acetate in the gastrointestinal tract. How- 

 ever, Kemmerer et al., 2Si in the same year, found that xanthophylls and 

 chlorophylls, when fed with carotene dissolved in cottonseed oil, decreased 

 the effectiveness of carotene for liver storage of vitamin A by about 20%. 



272 R. W. Jackson, J. Nutrition, 7, 607-616 (1934). 



273 A. E. Mahle and H. M. Patton, Gastroenterology, 9, 44-53 (1947). 



274 H. S. Mitchell, Proc. Soc. Exptl. Biol. Med., 31, 231-233 (1933). 

 276 T. Moore, Biochem. J., 23, 1267-1272 (1929). 



276 M. J. Burns, S. M. Hauge, and F. W. Quackenbush, Arch. Biochem., 30, 347-350 

 (1951). 



277 T. K. With, Nord. Med., 3, 2468-2470 (1939). 



278 T. K. With, Z. Vitaminforsch., 10, 1-6 (1940). 



279 T. K. With, Vitamine u. Hormone, 2, 369-399 (1942); Chem. Zentr., 114, I, 1286 

 (1943). 



280 K. C. D. Hickman and P. L. Harris, Advances in Enzymology, Vol. VI, Interscience, 

 New York and London, 1946, pp. 469-524. 



281 R. Major and B. M. Watts, J. Nutrition, 35, 103-116 (1948). 



J82 R. W. Swick and C. A. Baumann, Arch. Biochem. Biophys., 36, 120-126 (1952). 



283 W. C. Sherman, Proc. Soc. Exptl. Biol. Med., 65, 207-210 (1947). 



284 A. R. Kemmerer, G. S. Fraps, and J. De Mottier, Arch. Biochem., 12, 135-138 

 (1947). 



