FACTORS ALTERING CONCENTRATION OF CAROTENOIDS 505 



pigment. The symptoms of hypervitaminosis A have been reviewed by 

 Rodahl 916 and by Maddock et a/. 851 Other characteristic lesions, which 

 occurred in young animals, are skeletal fractures and external hemor- 

 rhages. 915 ' 917 



(e) The Effect of Carotene-free and Vitamin A-free Diets on Plasma Caro- 

 tene and Vitamin A. When vitamin A-free diets were given to rats, the 

 vitamin disappeared from the plasma within twenty days, 885 and definite 

 signs of avitaminosis A appeared in twenty-six days. On the other hand, 

 the depletion of the human subjects is much slower. Murrill and co- 

 workers 834 were unable to detect deficiency symptoms, other than a reduc- 

 tion of carotene and vitamin A in the blood, in either of two men who had 

 received a vitamin A-free diet for forty days. Even when the patients were 

 maintained on a diet low in vitamin A for six months, following a month of 

 high vitamin A intake, Wald et a/. 918 were unable to detect vitamin A- 

 deficiency symptoms in any of five men. 



On the other hand, Hsu 839 reported an average blood carotene figure of 

 23.8 microgram per cent (range 0-128), and a mean vitamin A value of 

 1.7 microgram per cent (range 0-8.1) in the case of eighty-five individuals 

 classed as vitamin A-deficient. Hartzler 919 was able to prove that the 

 level of serum carotene depends upon the presence of this substance in the 

 diet, and that of vitamin A upon the ingestion of carotene or vitamin A. 

 She demonstrated a progressive decrease both in carotene and in vitamin A 

 in a subject receiving a completely vitamin A-free diet. The blood plasma, 

 which contained 149 microgram per cent of carotene and 39.9 microgram 

 per cent of vitamin A at the start, had only 15 microgram per cent of 

 carotene and 22.8 microgram per cent of vitamin A at the end of the 140- 

 day depletion period. It i» likewise possible to produce experimentally, 

 and maintain over an indefinite period, by dietary means, a carotene-free 

 plasma without any symptoms of vitamin A deficiency. This can be done 

 by the administration of a carotene-free diet which contains an adequate 

 amount of preformed vitamin A. The alternative condition, namely one 

 in which carotene is present in the blood plasma without vitamin A, ob- 

 viously cannot occur, since a portion of the carotene will always be changed 

 to vitamin A in order to maintain a normal value of the latter compound 

 in the blood and tissues. 



(/) The Effect of Miscellaneous Substances on Plasma Carotene and Vita- 

 min A. The administration of mineral oil concomitantly with carotene 



917 K. Rodahl and T. Moore, Biochem. J., 37, 166-168 (1943). 



918 G, Wald, L. Brouha, and R. E. Johnson, Am. J. Physiol, 137, 551-556 (1942). 



919 E. Hartzler, J. Nutrition, 36, 381-390 (1948). 



