562 IX. CAROTENOIDS AND VITAMINS A 



failed to demonstrate increased vitamin A in human milk when fixed levels 

 of the vitamin were given in an oily medium; however, a marked increase in 

 the vitamin A content of milk occurred within twelve hours when similar 

 doses of vitamin A were administered in an aqueous medium. However, 

 when larger doses of vitamin A were given in the oil medium, an increase 

 in milk vitamin A was observed similar to that obtained when doses of the 

 vitamin were administered in aqueous dispersions. The same increase in 

 the blood level of vitamin A occurred. 



Parrish and co-workers^^^ reported that the effect of vitamin A supple- 

 ments on the vitamin A content of colostrum and of early milk of cows is 

 independent of the form or combination in which they are given. Thus, 

 vitamin A ester, vitamin A alcohol, and vitamin A alcohol plus tocopherols 

 appeared to have similar values in increasing the vitamin A content of co- 

 lostrum and of early milk. 



e. The Effect of the Thyroid Gland upon the Carotenoids and Vitamin A 

 in Milk. In general, an increase in thyroid secretion increases the vitamin 

 A content of milk, while a decrease in thyroid function, brought about by 

 the administration of thiouracil, results in a suppression of the vitamin A 

 in the milk. Chanda and co-workers*^^ were able to demonstrate these 

 changes in the goat after thyroxine or thiouracil, respectively, had been 

 administered. It was found that, on carotene-containing diets, the con- 

 tent of both carotene and vitamin A in the milk was increased by the ad- 

 ministration of thyroxine. On the other hand, when cows were placed on 

 a carotenoid-free diet, the proportion of vitamin A in unesterified form in- 

 creased, and this condition was further exaggerated when thyroxine was 

 given. ^^ Thyrotrophin, the thyroid-stimulating hormone, was also shown 

 to increase the proportion of vitamin A alcohol in cows on a carotenoid-free 

 diet.^^^ The carotenoid content of milk fat was found to be increased by 

 mastitis, while the vitamin A content was not changed; the proportion of 

 vitamin A in the alcohol form was increased in this infection. ^^^ 



(6) The Secretion of Carotenoids and 

 of Vitamin A into Eggs 



The largest proportion of the carotenoids in eggs consists of the caro- 

 tenols (xanthophylls). Whereas the ratio of carotenes to xanthophylls is 

 1 :3 in normal green food, the proportion in the eggs of hens is 1 :5 to 1:7^^^ 



««" D. B. Parrish, G. H. Wise, and J. S. Hughes, /. Dainj Set., 32, 458-464 (1949). 



8" R. Chanda, H. M. Clapham, and E. C. Owen, Biochem. J., 50, iii (1951). 



838 R. Chanda, H. M. Clapham, and E. C. Owen, Biochem. J., 52, xvii-xviii (1952). 



899 F. E. Jacob, Studies on the Carotenoid Pigments of Egg Yolks from Hens on Various 

 Diets, Thesis (Ph.D.), Univ. Missouri, 19.39; Univ. Microfilms, Ann Arbor, Publ. No. 

 225, 1941; Microfilm AbsL, Vols. 1-3 (1938-1941), Biol. Chem., pp. 1-3. 



