448 IX. CAROTENOIDS AND VITAMINS A 



Mg. per pound, serum carotene decreased progressively from 143.2 to 37 

 jug. %, that present in the yolks declined from 32.3 ± 2.0 to 8.4 ± 0.5 fig./ 

 g., liver carotene dropped from 7.8 to 2.7 Mg-/g-) while the carotenoid con- 

 tent of the body fat was usually, but not always depressed. Marked in- 

 creases in the vitamin A content of the serum, yolks, liver, and body fat 

 occurred concomitantly with the decreased carotenoid content. The 

 extent of the augmentation of vitamin A under these conditions far exceeded 

 that which would have occurred solely as the result of the increased caro- 

 tene breakdown. These data are of interest in cormection with those 

 reported by Hammon and Harshaw,^"- in which it was demonstrated that 

 fortified codhver oU possesses a factor which prevents the deposition of 

 xanthophyll in the shanks and skins of chicks. Proof that this phenomenon 

 is related to the increased vitamin A intake was furnished by Rubin and 

 Bird,^°* who reported that the pigment-depressing factor was, in fact, 

 vitamin A. Moreover, a similar carotenoid-depressing effect of massive 

 doses of vitamin A was observed in the case of turkeys, by Gurcay et 

 aL,^""* and also in ducks, by Rigdon and co-workers.-"^ On the other hand, 

 Hrubetz, Deuel, and Hanley^''^ failed to note a similar depression in the 

 carotene content of human milk when massive doses of vitamin A were 

 given to lactating mothers, although an increased vitamin A content in 

 the milk was observed. 



No satisfactory explanation for the carotene-depressing effect of massive 

 doses of vitamin A has been propounded. Because of the slowness of the 

 rate at which the hypocarotenoid condition develops (three to four weeks) , 

 it has been suggested that it occurs concomitantly with the development or 

 increased action of an enzyme system which destroys vitamin A. Because 

 of the similarity of the molecular structures of provitamins A and of vita- 

 min A, the former would probably also be attacked by this enzymatic mech- 

 anism. It is also possible that the change of j8-carotene ->- vitamin A may 

 be stimulated in this condition. It has not been determined whether or not 

 vitamin A exerts its effect on the carotene metabohsm in conjunction with, 

 or because of its action on the thyroid gland. 



(c) Miscellaneous Factors. Shaw et aZ.^°^ observed a decrease in the 

 plasma carotene of cows when ground soybeans were added to the diet in 



202 J. C. Hammon and H. M. Harshaw, Poultry Sci., 20, 437-444 (1941). 



""^ M. Rubin and H. R. Bird, Scisnce, 103, 584-586 (1946). 



204 R. Gurcay, R. V. Boucher, and E. W. Callenbach, /. Nutrition, 41, 565-582 

 (1950). 



206 R. H. Rigdon, J. C. Rude, and J. G. Bieri, Arch. Pathol., 52, 299-314 (1951). 



206 M. C. Hrubetz, H. J. Deuel, Jr., and B. J. Hanley, /. Nutrition, 29, 245-254 

 (1945). 



