FACTORS ALTERING CONCENTRATION OF CAROTENOIDS 497 



the administration of carotene is followed only by a rise in vitamin A in the 

 blood. 



(b) The Effect of Ingested Vitamin A on the Level of Plasma Vitamin A. 

 When vitamin A is administered as the ester or alcohol, a prompt increase 

 is noted in the vitamin A ester in the blood, which usually reaches the 

 maximum after three hours. The concentration cannot be increased to 

 any marked extent by the continued administration of this vitamin. 

 However, there did appear to be a slight effect on the postabsorptive blood 

 levels when single large doses were given to individuals previously "satu- 

 rated" with vitamin A as the result of an ample feeding of this vitamin. 

 Ralli and her colleagues 836 found higher maximum values for serum vitamin 

 A in men after the administration of 30,000 jug- (100,000 I.U.) of vitamin 

 A than after 6000 M g- (20,000 I.U.) had been given. However, in both 

 series of tests, normal values for serum vitamin A were found within twenty- 

 four hours. 



Lewis et al. S8i demonstrated that, in the case of rats, a direct relationship 

 obtains between the intake of vitamin A and the plasma level of this 

 component. These results are summarized in Table 19. 



Table 19 



Relation of Vitamin A Intake in the Eat to Gain in Weight 



and to Vitamin A Content of Blood Plasma, Liver, and Retina" 



° Data adapted from J. M. Lewis, O. Bodansky, K. G. Falk, and G. McGuire, J. 

 Nutrition, 23, 351-363 (1942). 



6 Experiments continued 4 weeks only. Rats sacrificed 48 hours after last vitamin A 

 dosage. 



e Averages for 14 only; 6 animals died during experiment. 



It will be noted that the optimum effect on weight gain of rats over a 

 sLx- weeks period after weaning occurs when 7.5 /xg. of vitamin A are ad- 



884 J. M. Lewis, O. Bodansky, K. G. Falk, and G. McGuire, J. Nutrition, 23, 351-363 

 (1942). 



