DIGESTION, ETC. OF CAROTENOIDS IN THF G.I. TRACT 303 



Table 7 



Effect of Thyroxine and Thiouracil on the Digestibility of Carotene 

 in Lactatino Cows and Goats" 



° Data adapted from R. Chanda, H. M. Clapham, M. L. McNaught, and E. C. Owen, 

 Biochem. J., SO, 95-99 (1951). 



h Animal died of hyperthyroidism before third period. 



(4) Changes in the Carotenoids in the Intestinal Wall 



The mechanism by which the carotenoids are carried into the intestinal 

 epithelia and from there into the blood stream is not clear. It is believed 

 that the bile salts provide a mechanism for their transfer into the in- 

 testinal cell in much the same way that they function in the absorption 

 of fat. 



The changes which take place in the carotenoids in the epithelial cells 

 must vary according to the species of the animal. Thus, in animals 

 whose blood and lymph contain no carotenoids, the intestinal wall is 

 obviously one site of breakdown of these substances. Whether or not 

 this cleavage of the carotenoids is limited to the provitamins A is not cer- 

 tain; here again there must necessarily be species variations. On the 

 other hand, it has not been determined whether animals like the dog, 

 cow, and man, which may have carotene in the blood stream, possess 

 any power to split the carotenoids in the intestinal wall. 



Other changes which take place in the epithelial cells of the intestine 



