DIGESTION, ETC. OF CAROTENOIDS IN THE G.I. TRACT 299 



tocopherols were fed with carotene to rats or to men, almost twice the 

 amount of provitamin A was recoverable from the feces. Guggenheim 343 

 has confirmed the increased fecal excretion of carotene which results 

 when vitamin E is fed. This worker also reports a greater utilization of 

 carotene as demonstrated by the vitamin A storage test; it is concluded 

 that vitamin E functions by protecting carotene and vitamin A from 

 oxidation while in the intestine. This brings about both increased ab- 

 sorption and greater fecal excretion. Hebert and Morgan 344 reported 

 that the addition of 0.5 mg. daily of a-tocopherol to the diet of partially 

 depleted rats increased the liver storage of vitamin A when carotene was 

 given; however, no augmentation of liver vitamin A occurred when 

 vitamin A itself was given. 



Although there seems to be adequate proof that moderate doses of a- 

 tocopherol protect carotene from oxidation and enhance its value as a 

 source of vitamin A, there are at least two reports which indicate that 

 large doses of this antioxidant have the opposite effect. Thus, Johnson 

 and Baumann 345 found that, when 5 or 10 mg. of a-tocopherol was fed 

 simultaneously with jS-carotene, the stores of vitamin A in the liver were 

 much lower than was the case when the tocopherol was not given. Intra- 

 peritoneal^ injected tocopherol also interfered with the utilization of f3- 

 carotene; however, when the tocopherol was given eight hours after the 

 carotene, no comparable interference with the storage of vitamin A was 

 noted. The effect of high levels of tocopherol on vitamin A storage is 

 presumably not concerned with the absorption of carotene, since the fecal 

 excretion of this provitamin A was no greater in these cases than in con- 

 trol tests. High and collaborators 346 reported that large amounts of 

 tertiary butylhydroquinone or octylhydroquinone also decreased the 

 utilization of carotene for tissue deposition of vitamin A, whereas small 

 amounts of octylhydroquinone were shown to augment vitamin A stor- 

 age. On the other hand, large amounts of octylhydroquinone were more 

 effective than were smaller quantities in inhibiting the oxidative decom- 

 position of carotene in in vitro tests. The same situation was shown to 

 obtain in the case of vitamin A. It is postulated that, when these sub- 

 stances are present in large amounts in vivo, the utilization of carotene 

 may be impaired, due to interference with the enzymatic conversion of 

 carotene to vitamin A. 346 



343 K. Guggenheim, Biochem. J., 38, 260-264 (1944). 



344 J. W. Hebert and A. F. Morgan, J. Nutrition, 50, 175-190 (1953). 



346 R. M. Johnson and C. A. Baumann, /. Biol. Chem., 175, 811-816 (1948). 



346 E. G. High, L. A. Woods, Jr., and S. S. Wilson, J. Biol. Chem.., 195, 787-793 (1952). 



