DIGESTION, ETC. OF CAROTENOIDS IN THE G.I. TRACT 285 



mals, such as man, cattle, and dogs, in which carotene is present as such 

 in the blood. 



Although it is generally agreed that carotene cannot be absorbed in the 

 stomach, it is believed that the small intestine is the principal site for 

 absorption. Ronning and Knodt 218 reported that a low concentration of 

 carotene obtains in the middle third of the small intestine after a single 

 administration of this compound to young male Holstein calves. While 

 it is possible that this low concentration of carotene in the wall of the 

 gastrointestinal tract may be evidence of carotene conversion to vitamin 

 A in this location, this hypothesis must be discounted, since it was not 

 possible to demonstrate concurrent increases in vitamin A under these 

 conditions. 



(a) Factors That Affect the Absorption of fi-Carotene. Although the 

 investigation of the factors that influence the absorption of carotenoids 

 has been largely carried out with tf-carotene, it seems probable that these 

 conditions may likewise be applicable to the absorption of other carotenoids. 

 Since these studies have been almost entirely carried out with /^-carotene, 

 they are listed under this compound. 



a'. Surface Area and the Absorption of /3-Carotene: Shaw and Deuel 219 

 have shown that the absorption of /3-carotene, fed in cottonseed oil, to 

 rats is a function of surface area. After the feeding of massive doses of 

 approximately 4 mg. (4000 ^g.) in a single dose, ^-carotene was absorbed 

 at the rate of approximately 110 jug- per 100 sq. cm. per hour. After 

 twelve hours, less than 20% of the carotenoid could be isolated from the 

 lumen of the gut; however, at twelve and at eighteen hours, approxi- 

 mately 50% of the administered dose could be recovered from the wall 

 of the intestine. After forty-two hours, almost 20% of the carotenoid 

 fed could still be extracted from the gut wall. In view of our more recent 

 knowledge that carotenes are converted to vitamin A in the Avail of the 

 intestine of the rat, the high concentration in this tissue over a prolonged 

 period is not surprising. Vavich and Kemmerer 220 reported that the 

 size of the rats markedly influences the extent of utilization of carotene 

 for vitamin A storage in the liver. Thus, when GO Mg- of /3-carotene 

 equivalents were fed, the combined amount of vitamin A stored in the 

 liver and kidneys was higher in rats weighing approximately 50 g. than 

 it was in groups of rats averaging 100 g. in weight. The fate of this caro- 

 tene is discussed later (see page 303). 



218 M. Ronning and C. B. Knodt, J. Dairy Sci., 35, 283-291 (1952). 



219 R. J. Shaw and II. J. Deuel. Jr., J. Nutrition, 27, 395-401 (1944). 



220 M. G. Vavich and A. R. Kemmerer, /. Nutrition, 40, 605-610 (1950). 



