442 IX. CAROTENOIDS AND VITAMINS A 



latter investigators were able to demonstrate only a slight inflection in the 

 absorption curve at 328 m/z, and they did not succeed in establishing any 

 other proof of the presence of vitamin A. It would appear to the author 

 that the liver affords an additional site, other than the gut wall, for the 

 transformation of /3-carotene into vitamin A in species whose tissues con- 

 tain carotene; the possibility of this change in the livers of the animals not 

 normally containing carotene in the tissues and blood must still be con- 

 sidered questionable. 



Samaras and Hingerty^^'^ suggested that, in addition to the liver, the 

 reticuloendothelial (R.E.) system plays a role in the conversion of caro- 

 tene to vitamin A. When carotene was given parenterally, in aqueous 

 solution, to normal rats, it was found to be converted to vitamin A within 

 two hours. The rate of change was increased eighteen hours after the R.E. 

 system in the normal rat had been blocked by the administration of trypan 

 blue. It was believed that the dye stimulated the activity of the R.E. 

 system. On the other hand, in the case of the vitamin A-deficient rat, the 

 injection of the dye markedly reduced the ability of the rat to form vitamin 

 A from carotene. 



There is now increasing evidence that the conversion of carotene to 

 vitamin A can occur in tissues other than the small intestine, not only in 

 the case of the group of animals whose blood and tissues contain appreciable 

 amounts of carotene, but also in the case of the types which normally do 

 not have the carotenoids in the blood or tissues. Thus, Bieri and Sand- 

 man ^^^ observed growth in vitamin A-deficient rats when j8-carotene, solu- 

 bilized in water by means of Tween 40, was given by the intramuscular 

 route in amounts as small as 1.6 ^g. daily. However, four to six times as 

 much carotene was required to produce maximum growth when it was 

 administered by the parenteral route as when it was given orally. These 

 workers were able to obtain their results Avith aqueous suspensions of /3- 

 carotene, but not when the carotene was given in oil solution. This con- 

 firms the results of Sexton et al.^^ Bieri and Schultze^^^ noted small amounts 

 of vitamin A in the blood and kidneys of normal and of hypothyroid, 

 vitamin A-depleted rats after the intramuscular injection of carotene solu- 

 bilized with Tween 80, although no significant increase in liver vitamin A 

 was observed. Under these conditions, the administration of thiouracil 

 had Uttle or no effect upon the vitamin A level. Bieri and Pollard^"" 

 later reported that an aqueous suspension of j8-carotene in Tween 40 pro- 

 's' S. C. Samaras and D. J. Hingerty, Am. J. PhijsioL, 169, 588-589 (1949). 

 158 J. G. Bieri and R. P. Sandman, Proc. Soc. Exptl. Biol. Med., 77, 617-619 (1951). 

 '59 J. G. Bieri and M. O. Schultze, Arch. Biochem. Biophijs., 34, 280-284 (1951). 

 '«> J. G. Bieri and C. J. Pollard, Federation Proc, 12, 409 (1953). 



