426 IX. CAEOTENOIDS AND VITAMINS A 



of the bile salts. The phospholipid, lecithin, also enhances the absorption 

 of carotene. It has been reported that the utilization of /3-carotene is 

 augmented when it is fed as a component of margarine.^'' It is suggested 

 that the lecithin, and the mono- and diglycerides present in this product, 

 aid in absorption. 



A nmnber of workers*^"^* observed that carotene was as well absorbed, 

 or even better, when administered in an aqueous colloidal solution solu- 

 biUzed by dispersing agents, for instance, "Tween 40" (polyoxyethylene 

 sorbitan monopalmitate) than when given in an oil solution. Vavich and 

 co-workers^* fomid that carotene was better utihzed when fed as an homog- 

 enate in non-fat milk than when it was homogenized in water. 



The thyroid gland exerts an important role in the absorption of carotene. 

 Johnson and Baumann*^ were the first to demonstrate in an unequivocal 

 fashion that less vitamin A accumulated in the livers and kidneys of rats 

 rendered hypothyroid with thiouracil than was the case with normal rats 

 receiving the same amount of carotene. Conversely, the livers of hyper- 

 thyroid rats contained more vitamin A than did those of the normal con- 

 trols. However, this phenomenon was not related to the increased oxida- 

 tion caused by the thyroid, as no increase in vitamin A storage was noted 

 in rats having increased oxygen utihzation as the result of the administra- 

 tion of 2,4-dinitrophenol. 



Goodwin^" called attention to the three possible explanations of the above 

 experimental data, namely (1) that the thyroid controls the conversion of 

 carotene into vitamin A, (2) that it controls the stability of carotene in the 

 lumen of the intestine, and (3) that it regulates the absorption of carotene 

 from the lumen. Cama and Goodwin^^ also demonstrated that, in the case 

 of the rat, the absorption of carotene is increased when thyroxine is given 

 and is decreased after the thyroid antagonist, thiouracil, is administered. 

 They are of the opinion that possibility S above is ruled out, since thioura- 

 cil was found to have no effect on the stability of jS-carotene in the intestine. 

 However, it was shown that the fecal excretion of carotene was increased 



30 H. J. Deuel, Jr., S. M. Greenberg, E. E. Savage, and D. Melnick, /. Nutrition, 

 43,371-388(1951). 



31 S. Y. Thompson, R. Braude, A. T. Cowie, J. Ganguly, and S. K. Kon, Biochem. J., 

 U, ix-x (1949). 



32 G. H. Wise, N. L. Jacobson, R. S. Allen, and S. P. Yang, J. Dairy Set., 32, 711 

 (1949). 



33 M. J. Burns, S. M. Hauge, and F. W. Quackenbush, Arch. Biochem., SO, 341-346 

 (1951). 



'* M. G. Vavich, J. W. Stull, N. Raica, and A. R. Kemmerer, Arch. Biochem. Bio- 

 phys.,55, 310-314 (1955). 



35 R. M. Johnson and C. A. Baumann, J. Biol. Chem., 171, 513-521 (1947). 



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



