322 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



Any beneficial effect which a-tocopherol acetate exerts on the utilization 

 of vitamin A was shown to be due to the a-tocopherol available in the 

 intestine during the interval between hydrolysis and absorption. The 

 prolonged effect of the administration of a-tocopherol during the vitamin 

 A assay period is evident from the fact that the tocopherol-supplemented 

 animals survived 30 to 80% longer after the assay than did the unsupple- 

 mented controls. Major and Watts 281 noted that, when high levels of 

 tocopherol were fed or injected into rabbits on a purified diet, the body 

 fat and meat were protected from rancidity. However, no protection 

 from rancidity was afforded the fat or tissues by the administration of 

 tocopherol when a natural diet was employed. 



b. The Esterification of Vitamin A in the Intestinal Wall. Some mech- 

 anism must function to produce esterification of vitamin A alcohol. This 

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

 largely in the form of the ester, irrespective of whether vitamin A alcohol, 

 vitamin A ester, or /3-carotene is administered. 



Proof that esterification of vitamin A occurs in the intestinal wall is 

 afforded by examination of the vitamin A present in this structure. 

 Thompson et a/. 259 demonstrated that the proportions of vitamin A alcohol 

 and of ester in the wall were about equal; both forms appeared after 

 vitamin A alcohol, vitamin A ester, or carotene had been given. In 

 later work 471 it was indicated that the esterified vitamin A in the intestinal 

 wall approximates 75% of the total. 



c. The Transformation of Retinene Into Vitamin A. Ball, Glover et 

 a/. 472 and Glover and co-workers 473 found that vitamin A-deficient rats 

 were able to convert retinenei (vitamin A x aldehyde) rapidly into vitamin 

 A x , either in the mucous membranes of the gut or in the liver. This change 

 could be noted after retinenei was given orally, as well as following sub- 

 cutaneous injection. It is believed that the transformation is a quantita- 

 tive one. This implies the presence of an efficient reductase to reduce 

 the aldehyde to the alcohol. According to Gounelle et a/., 474 when retinene 

 originating from the oxidation of vitamin A or from cleavage of carotene 

 is ingested by man, it induces a rise in plasma vitamin A which reaches a 

 maximum in six hours. 



Retinenei appears to be absorbed in the same way as vitamin Ai. Glover 



471 S. Y. Thompson, R. Braude, M. E. Coates, A. T. Cowie, J. Ganguly, and S. K. 

 Kon, Brit. ./. Nutrition, 4, 398-421 (1950). 



472 S. Ball, J. Glover, T. W. Goodwin, and R. A. Morton, Biochem. ./., 41, xxiv (1947) 



473 J. Glover, T. W. Goodwin, and R. A. Morton, Biochem. ./., 43, 109-114 (1948). 



474 H. Gounelle, G. Marnay, R. Cheroux, and Y. Raoul, Compt. rend. soc. biol, 146, 

 523-525(1952). 



