METABOLISM OF CAROTENOIDS AKD VITAMINS A 555 



four hours was excreted in the urine in nephritis or in pneumonia in man; 

 hirge amoiuits were Ukewise found in dog urine, but none was noted in the 

 urine of normal or diseased cats, rabbits, or rats.^" It was observed that 

 while normal urine Avould not take up vitamin A when shaken with halibut 

 liver oil, urines containing vitamin A retained still more vitamin A under 

 these conditions. Presumably there was a sufficient excess of urinary pro- 

 tein so that more vitamin A could be bound. ^'^ CateP^ also found vitamin 

 A in the urine of healthy dogs but never m rabbits, which are herbivorous. 

 Yitaminuria was occasionally noted in the case of healthy premature and 

 full -term newborn infants, but not in older children, except in nephritis 

 and in other diseases. In these cases the vitamin A concentration in the 

 blood was not decreased. 



(5) The Secretion of Carotenoids 

 and of Vitamin A into Milk 



In the case of lactating animals, large amounts of carotenoids and of 

 vitamin A are secreted by the mammary gland. The quantity of these 

 components, as well as the ratio in which they appear in milk, vary with 

 species, season, and diet. The composition of milk (excluding the fat- 

 soluble vitamin content), and the factors which determine the lipid com- 

 ponents, are discussed in The Lipids, Vol. II, pages 791 to 810. A brief de- 

 scription of the factors affecting the carotene and vitamin A content of 

 milks is included in The Lipids, Vol. I, pages 685-687. 



/3-Carotene is the chief carotenoid in milk fat. In some cases, small 

 amounts of a-carotene may also occur when it is present in the rations fed 

 the cows.®^- According to Chanda,^^ /3-carotene makes up 65 to 85% of 

 the total carotenoids of cow's milk. Lutein is regularly present in cow's 

 milk and in butter.''^ Other xanthophylls may also be present. Gillam 

 and Heilbron®^ observed the occurrence of iycopene in butter and milk. 



Most of the fat-soluble yellow pigment in colostrum and in milk is caro- 

 tene.^^'^ Chanda^^^ found no carotenoids in goat's milk. In cow's milk the 

 carotenoid content did not change as lactation advanced. The average 

 amount was 5.1 /xg/g- of fat. 



Vitamin A is present in milk from all species, but the quantity varies 

 under different conditions. The vitamm A is largely in the form of the 

 ester, although Chanda^^ reported that 5 to 8% of the vitamin A in cow's 



858 W. Catel, Klin. Wochschr., 17, 574-575 (1938). 



859 R. Chanda, Biochem. J., 52, ii (1952). 



^^ D. B. Parrish, G. H. Wise, and J. S. Hughes. /. Biol. Chem.. 167. 673-678 (1947). 



