DIGESTION, ETC. OF CAROTENOIDS IN THE G.I. TEACT 305 



l>ut also in the chicken, 363,364 in the guinea pig, 365 in the pig ; 258,259,366 an( j m 

 goats, sheep, and rabbits. 263264 Proof that the material formed in the 

 intestinal wall of rats after the administration of carotene actually is 

 vitamin A was presented by Mattson. 367 The fat-soluble material from 

 the intestinal walls of rats previously fed /3-carotene was extracted, after 

 saponification of the tissue, with Skellysolve A, and most of the vitamin 

 A was removed by extraction of the petroleum ether solution with 90% 

 methanol. After further purification, the active material was separated 

 chromatographically. It was proved to be identical with vitamin A alco- 

 hol, both by spectroscopic examination and by virtue of forming a single 

 homogeneous chromatogram when mixed with known vitamin A. 



Popper and Greenberg 368 also reported experiments which can now be 

 interpreted as indicative of the extrahepatic conversion of carotene. 

 When the various organs of a series of vitamin A-depleted rats were 

 examined by the use of fluorescence microscopjr at intervals after the ad- 

 ministration of /3-earotene, fluorescence, due to the presence of vitamin A, 

 appeared in the liver after the carotene was given orally, but not when it 

 was administered by the parenteral route. This author sometimes de- 

 tected fluorescence in the intestinal wall before its demonstration in the 

 liver, but usually it was noted in the latter organ first. 



Another confirmation of the extrahepatic conversion of carotene to 

 vitamin A has been adduced by Krause and Pierce. 369 These workers 

 found that, in rats which had undergone ligation of the portal vein, so 

 that hepatic circulation was reduced to 10% of the normal, the amount of 

 vitamin A in the serum increased after the oral administration of carotene. 

 Even under such severe conditions, no carotene was found in the blood. 

 This would indicate that the transformation of carotene to vitamin A 

 occurs without any assistance from the liver. 



In addition to the demonstration of the conversion of (S-carotene to 

 vitamin A by in vivo technics, Wiese et al. m succeeded in bringing about 

 the same change by an in vitro procedure. Thus, it was shown that 

 vitamin A was produced when a carotene solution in Tween was intro- 

 duced into the intestine of vitamin A-deficient rats, after which the gastro- 



3 « S. Y. Thompson, M. E. Coates, and S. K. Kon, Biochem. J., 46, xxx (1950). 

 3fi4 A. L. S. Cheng and H. J. Deuel, Jr., J. Nutrition, 41, 619-628 (1950). 

 366 L. Woytkiw and N. C. Esselbaugh, J. Nutrition, 43, 451-458 (1951). 



366 M. E. Coates, S. Y. Thompson, and S. K. Kon, Biochem. J., 46, xxx-xxxi (1950). 



367 F. H. Mattson, J. Biol. Chem., 176, 1467-1468 (1948). 



368 H. Popper and R. Greenberg, Arch. Pathol., 32, 11-32 (1941). 



369 R. F. Krause and H. B. Pierce, Arch. Biochem., 19, 145-148 (1948). 



370 C. E. Wiese, J. W. Mehl, and H. J. Deuel, Jr., Arch. Biochem., 15, 75-79 (1947). 



