438 IX. CAROTENOIDS AND VITAMINS A 



in the intestinal wall than in the liver for four hours after the carotene 

 feeding. ^^- Mattson^** proved that the material accumulating in the intes- 

 tinal wall under these conditions was actually vitamin A. The intestinal 

 wall was shown to be a site of conversion of )3-carotene to vitamin A not 

 only in the case of the rat,""-^**"^^^ but also in the guinea pig,^" the pigji34,i38 

 and in rabbits, goats, and sheep, ^^^ all of which belong to Group C. Stallcup 

 and Herman^^" proved that the intestine is one of the sites for the conver- 

 sion of carotene to vitamin A in dairy calves (which belong to Group B). 

 Thompson et a/.^*^ and Cheng and DeueP^- also noted that the intestine is 

 the site for the conversion of carotene in the chicken, which we have 

 assigned to Group D. 



Further support for the thesis that the intestinal wall is the site of the 

 conversion of carotene into vitamin A can be derived from in vitro studies. 

 Thus, Wiese and her collaborators^*^ demonstrated the synthesis of vita- 

 min A from carotene when suspensions of the chromogen in Tween 80 

 (PSM) were allowed to incubate in rat intestine. Rosenberg and Sobel^** 

 also confirmed these results with rat intestine, while McGilhvray^*^ demon- 

 strated that highly significant increases occurred in sections of sheep intes- 

 tine which had been incubated with jS-carotene. The fact that thoracic 

 lymph of a wide variety of animals belonging to Group C contains no appre- 

 ciable carotene, but only increased proportions of vitamin A, after the pro- 

 vitamin A is introduced orally, affords additional excellent proof of the syn- 

 thesis of vitamin A from carotene at some stage between the lumen of the 

 gut and the lacteals of the villi. The intestinal mucosa would obviously 

 be the most probable site for this change. The reader is referred to the 

 section on transport (see page 455) for a further discussion of the relation of 

 vitamin A in the lymph and blood to administered carotene. 



132 F. H. Mattson, J. W. Mehl, and H. J. Deuel, Jr., Arch. Biochem., 15, 65-73 (1947). 



133 F. H. Mattson, /. Biol. Chem., 176, 1467-1468 (1948). 



134 S. Y. Thompson, J. Ganguly, and S. K. Kon, Brit. J. Nutrition, 1, v (1947); 3, 

 50-78 (1949). 



136 J. Glover, T. W. Goodwin, and R. A. Morton, Biochem. J., 41, xlv (1947); 43, 

 512-518 (1948). 



136 A. B. McCoord and S. W. Clausen, Ahst. 114th Meeting, Am. Chem. Soc., Div. 

 Biol. Chem., Washington, Aug. 30, 1946, p. 16C. 



137 L. Woytkiw and N. C. Esselbaugh, /. Nutrition, 43, 451-458 (1951). 



138 M. E. Coates, S. W. Thompson, and S. K. Kon, Biochem. J., 46, xxx-x.xxi (1950). 



139 T. W. Goodwin and R. A. Gregory, Biochem. J., 43, 505-512 (1948). 

 i« O. T. Stallcup and H. A. Herman, /. Dairij Sci., 33, 237-242 (1950). 



1" S. Y. Thompson, M. E. Coates, and S. K. Kon, Biochem. J., 46, xxx (1950). 

 i« A. L. S. Cheng and H. J. Deuel, Jr., /. Nutrition, 41, 619-628 (1950). 

 1" C. E. Wiese, J. W. Mehl, and H. J. Deuel, Jr., Arch. Biochem., 15, 75-79 (1947). 

 1" A. Rosenberg and A. E. Sobel, Arch. Biochem. Biophys., 44, 320-325 (1953). 

 i« W. A. McGillivray, Australian J. Sci. Research, B4, 370-376 (1951). 



