TRANSPORT OF CAROTENOIDS AND FAT-SOLUBLE VITAMINS 333 



demonstrated that dosage of guinea pigs with either carotene or vitamin 

 A caused an increase in the vitamin A content of the mesenteric lymphatics, 

 as well as of the blood of the dorsal aorta. Carotene absorption was re- 

 ported to be negligible in the guinea pig, as demonstrated by its absence 

 from the lymph. Absorption of carotene or of vitamin A could not be 

 shown to take place via the portal vein. McGillivray 371 also reported 

 high levels of vitamin A in the intestinal lymph of sheep and of a bullock 

 after carotene feeding. This is interpreted as evidence for the view that 

 the intestine may be the site of conversion of carotene to vitamin A in 

 cattle as well as in sheep. 



The vitamin A found in lymph after the administration of carotene has 

 been shown to consist almost exclusively of vitamin A ester. 231 - 259,471 

 The proportion of vitamin A ester to that of vitamin A alcohol in the lymph 

 after carotene administration was similar to that observed when vitamin 

 A was given in either alcohol or ester form. 259 - 471 



The portal blood has been shown to play a negative role in the trans- 

 port of carotene or of vitamin A formed from it in the intestinal mucosa. 

 Thus, Goodwin, Dewar, and Gregory 263 reported that carotene was ab- 

 sent not only from the systemic blood of sheep and goats, but also from the 

 portal blood. 



Considerable evidence has been presented which indicates that vitamin 

 A from ingested carotene or from ingested vitamin A is transported ex- 

 clusively by way of the lacteals and lymphatics. In the first place, the 

 quantitative recovery of ingested vitamin A in the lymph indicates that 

 this is the sole pathway. 562 Secondly, Thompson et al. 471 proved that 

 no differences could be demonstrated between the level of vitamin A in 

 systemic and in portal blood of pigs after /3-carotene had been given in 

 peanut oil, or after the administration of vitamin A ester. Eden and 

 Sellers 563 reported that vitamin A values were higher in the systemic blood 

 than in the portal blood in bullocks which had been given large doses of 

 vitamin A two to twenty-four hours before slaughtering. The best proof, 

 however, was furnished by the experiments of Thompson et al., i71 which 

 indicated that no increase in the vitamin A level of blood or liver occurred 

 in rats after the feeding of carotene when the lymph was diverted and pre- 

 vented from emptying into the blood stream. 



(2) The Transport of Vitamin A in the Lymph and Blood 



The classical proof that vitamin A is transported from the intestine ex- 

 clusively in the chyle is that of Drummond, Bell, and Palmer, 562 who were 

 563 E. Eden and K. C. Sellers, Biochem. J., 42, xlix (1948). 



