456 IX. CAROTENOIDS AND VITAMINS A 



The latter result is of particular interest, since the blood of the bullock nor- 

 mally contains carotene. This corroborates the opinion that the conver- 

 sion of carotene into vitamin A occurs to some extent even in the case of 

 species which absorb carotene in unchanged form. 



On the other hand, no carotene or vitamin A is transported from the 

 intestine via the portal route after carotene feeding in the case of guinea 

 pjggi37 Qj. |j^ i\yQ^ Qf sheep and goats. ^^^ Moreover, Thompson et al^^^ re- 

 ported that the level of vitamin A in systeinic and in portal blood of pigs 

 increased at approximately the same rate after carotene or vitamin A had 

 been administered in peanut oil. In fact, Eden and Sellers^^^ recorded a 

 higher content of \dtamin A in systemic than in the portal blood of bullocks 

 immediately after preformed Adtamin A had been given. Another proof of 

 the fact that transport of vitamin A occurs solely by way of the lymphatics 

 and not by the portal vein is that no increase occurs in the level of vitamin 

 A in the blood or liver after the feeding of carotene when the lymph is di- 

 verted and prevented from emptying into the blood stream. "^ The vita- 

 min A present in lymph after the administration of ;5-carotene is present al- 

 most exclusively in ester form.^^^'^^^ 



Both the pathway of transport and the extent of esterification of \'ita- 

 min A are the same whether vitamin A is given as the alcohol or as the ester, 

 and are similar to those observed after the administration of carotene. As 

 already noted, the fact that a quantitative recovery of administered vita- 

 min A could be demonstrated in the lymph of the patient suffering from 

 chylothorax-^^ constitutes proof that the lymphatics are the sole route of 

 transport from the intestine to the liver. Moreover, a number of investi- 

 gators^^*'^'^'2^^'2^^'2"'2^2 proved that the portal vein does not transport pre- 

 formed -vitamin A from the intestine to the liver and other internal organs. 

 Radice and Herraiz^^^ presented the only evidence for transport of vitamin 

 A by the portal route ; they observed a fluorescence of portal blood similar 

 to that of lymph, which was attributed to the presence of vitamin A. 

 However, the bulk of evidence is against the hypothesis that the portal 

 vein serves as an avenue for the transport of vitamin A after the adminis- 

 tration of carotene or vitamin A. 



5. Carotenoids and Vitamins A in the Blood 



Although the portal circulation does not serve as the route of transfer of 

 the carotenoids or of vitamins A from the gut wall to the internal organs. 



250 T. W. Goodmn, A. D. Dewar, and R. A. Gregory, Biochem. J., 40, Ix-lxi (1946). 



^1 E. Eden and K. C. Sellers, Biochem. J., 4^, xlix (1948). 



2" E. Eden and K. C. Sellers, Biochem. J., 44, 264-267 (1949). 



253 J. G. Radice and M. L. Herraiz, Rev. asoc. med. argentina, 287-292 (1947). 



