FACTORS ALTERING CONCENTRATION OF CAROTENOIDS 



499 



level was 124 microgram per cent; on the other hand, when the dosage was 

 only 7500 ng. of vitamin A, the highest value for vitamin A in the serum 

 was 68 microgram per cent. In both cases, the peak values were obtained 

 five hours after the ingestion of the vitamin. The basal values for vitamin 

 A were reached twenty-four hours after the lower dose of vitamin A ; the 

 vitamin A levels were still slightly elevated in the twenty-four hour samples 

 following the higher vitamin A intake (15,000 /xg.). 



800 



■tfours 

 Fig. 10. A typical vitamin A tolerance curve. "N" represents the basal level. 

 Shaded area represents the increase in vitamin A level for the two- to eight-hour 

 period, expressed in microgram hours. The calculated area = (A + C + E) + 

 l.5(B + D) - GN.™ 



Week and Sevigne 129 carried out an extensive series of tests with human 

 subjects, to whom they gave 134,000 jug- of vitamin A in the form of vita- 

 min A alcohol, acetate, or palmitate, along with 50 g. of a commercial 

 brand of margarine. A typical curve for assessing the increase in blood 

 vitamin A is shown in Figure 10. A comparison of the amount of vita- 

 min A in the plasma as the ester or as the alcohol is given in Table 21. 



The administration of vitamin A as the free alcohol, acetate, or natural 

 ester in the amount of 134,000 fig. gives rise to a curve for plasma vitamin 

 A which reaches the maximum in five hours, for male subjects. In most 

 cases of women, the peak is reached under comparable conditions in four 

 hours. The figures for plasma vitamin A remain somewhat above the 

 basal value, even after twenty-four hours. There is practically no change 

 in the value for vitamin A alcohol during the entire experimental period. 

 On the other hand, there is a hundred-fold increase in the concentration of 

 vitamin A ester. Although vitamin A alcohol constitutes 80 to 90% of the 



