DIGESTION, ETC. OF CAROTENOIDS IN THE G.I. TRACT 289 



suspension containing 10% of Tween was somewhat better than in rats 

 receiving the chromogen in an oil solution. Eaton and co-workers 246 

 found that calves, depleted of vitamin A, had higher plasma levels of R- 

 carotene, and greater amounts of vitamin A in the liver and lung after 

 an aqueous suspension of carotene had been given intravenously than 

 following its oral administration. Jacobson and co-workers 247 found that, 

 when carotene and vitamin A were dispersed in milk and fed to calves 

 from a bottle with a nipple, the supplements were more rapidly absorbed 

 than when administered by stomach tube. Moreover, the rate of ab- 

 sorption of /3-carotene and vitamin A was somewhat less rapid when the 

 concentrates were fed in gelatin capsules than when the foregoing proce- 

 dures were employed. Tomarelli and associates, 248 and more recently 

 Bieri and Sandman, 249 reported that /3-carotene can be readily utilized 

 by rats when given parenterally, provided an aqueous suspension in 

 Tween 80 or Tween 40 is used. 



e'. The Effect of Thyroxine and Thiouracil on the Absorption of /3- 

 Carotene: When thyroxine is administered to rats, the absorption of /3- 

 carotene is improved; on the other hand, the administration of thiouracil 

 has been found to inhibit the absorption of this provitamin. 250 A similar 

 behavior on the part of these two drugs in causing an alteration in the co- 

 efficient of digestibility of carotene has recently been noted in the goat 

 and lactating cow 251 (see page 302). 



Although it was formerly claimed that thyroid-active materials ac- 

 celerate the conversion of /3-carotene into vitamin A, 252,253 more recent 

 data have failed to confirm these earlier observations. 254-256 If the sole 

 site of conversion of /3-carotene into vitamin A is in the wall of the in- 



246 H. D. Eaton, L. D. Matterson, C. F. Ilelmboldt, and E. L. Jungherr, /. Dairy Sci., 

 34, 1073-1080 (1951). 



247 N. L. Jacobson, G. II. Wise, R. S. Allen, and O. Kempthorne, J. Dairy Sci., S3, 

 645-656(1950). 



248 R. M. Tomarelli, J. Charbnev, and F. W. Bernhart, Proc. Soc. Exptl. Biol. Med., 

 63, 108-110 (1946). 



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



260 H. R. Cama and T. W. Goodwin, Biochem. J., 45, 236-241 (1949). 



261 R. Chanda, H. M. Clapham, M. L. McNaught, and E. C. Owen, Biochem. J., 50, 

 95-99 (1951). 



252 T. J. Balaba, J. Physiol. (U.S.S.R.), 29, 318-326 (1940). 



253 S. Kaplanskil and T. J. Balaba, Biokhimiya, 11, 327-331 (1946); Chem. Abst., 41, 

 507 (1947). 



254 H. R. Cama and T. W. Goodwin, Biochem. J., 45, 317-320 (1949). 



255 C. W. Lowry and J. R. Lowry, Arch. Biochem., 26, 287-290 (1950). 



256 J. G. Bieri and M. O. Schultze, Arch. Biochem. Biophys., 34, 280-284 (1951) 



