FACTORS ALTERING CONCENTRATION OF CAROTENOIDS 495 



ten days, plasma and kidney vitamin A was decreased, concomitantly 

 with an increase in the level of liver vitamin A. It is suggested that Com- 

 pound L may function by exerting a regulatory effect on the equilibrium 

 between liver and plasma vitamin A. 



c. The Effect of Diet on the Level of Carotene and Vitamin A in the 

 Blood, (a) The Effect of Ingested Carotene on the Level of Plasma Carotene 

 and Vitamin A . The amount of carotenoids present in ordinary meals has 

 little or no effect on the carotene or vitamin A content of the serum. 833 

 When large quantities of carotene are ingested, either in oil solution or by 

 the ingestion of foods rich in carotene, both the carotene and the vita- 

 min A content of the plasma are augmented. Getz 879 was able to increase 

 the plasma carotene of human subjects from 900 to 1100 microgram per 

 cent after feeding 120,000 ng. (120 mg.) of carotene. Vitamin A in the 

 plasma reached a maximum of only 51 microgram per cent (170 I.U.). It 

 was believed that this result indicated a relatively poor utilization of a 

 carotene in man ; the conversion of carotene to vitamin A was estimated at 

 15 to 20%. At low levels, the increase in blood carotene is proportional 

 to the dose. However, with gradually increasing doses, the rise in blood 

 carotene does not occur in proportion to the dosage; this is probably to be 

 ascribed to increasing losses in the feces. Vitamin A in the serum increases 

 in proportion to that of blood carotene after the administration of caro- 

 tene. 833,834 



When carotene is administered in a moderate dose, the maximum level 

 in the serum may not be reached for seven to ten hours after its administra- 

 tion, 880 in contradistinction to vitamin A, following which the peak of 

 serum vitamin A occurs within three to five hours. 881 Murrill et a/. 834 

 found that, when somewhat larger doses (80 mg.) were given, the maximum 

 blood carotene was noted in six hours, although a second increase in this 

 value occurred which reached a maximum figure twenty-four to forty- 

 eight hours after the original dosage. In the case of serum vitamin A, 

 only a single rise was experienced, and this was completed within nine hours. 

 On the other hand, when massive doses of carotene in oil (600 mg.) were 

 given human subjects, 880 the hypercarotenemia was prolonged for sixty to 

 seventy-two hours before the maximum value was obtained. In the experi- 



878 T. Reichstein, Helv. Chim. Acta, 19, 29-63, 402-412 (1936). 



879 H. R. Getz, "Induction of Vitamin A Deficiency in Man," presented at Vitamin 

 Conference, A. A. A. S., Gibson Island, July, 1944; cited by J. C. Fritz, Ann. Rev. Bio- 

 chem., 14, 525-560 (1945), p. 533. 



880 E. P. Ralli, H. Brandaleone, and T. Mandelbaum, J. Lab. Clin. Med., 20, 1266- 

 1275 (1935). 



881 S. W. Clausen, /. Am. Med. Assoc, 101, 1384-1388 (1933). 



