CAROTENOIDS AND VITAMINS A IN THE BLOOD 471 



take reached as high as 300 /xg. per day.^^" When a massive dose was given 

 (30,000 Mg. daily), a considerable increase in the plasma vitamin A was 

 noted; however, this last condition cannot be considered to be normal, 

 since the rats suffered from hypervitaminosis, and many of them (30%) 

 died during the six- week feeding period. 



When vitamin A was given to chickens in widely varied doses, no marked 

 variations in the plasma vitamin A levels were noted, in spite of the caro- 

 tene-depressing action of the vitamin, and the increased vitamin A levels 

 in the liver, body fat, and egg yolks. -"'^ The following are the average 

 figures for plasma vitamin A (in jug. %) at several levels of vitamin A in- 

 take (Mg. of vitamin A/lb. food): (in food), 139; 333, 166; 9,000, 134; 

 18,000,174:; 30,000,133; and 60,000, 207. Josephs^^'- observed that, when 

 carotene-free and vitamin A-free diets were fed to rats, the plasma was 

 free from detectable vitamin A within twenty days, and definite signs of 

 avitaminosis appeared within twenty-six days. Hartzler^^^ reported a 

 progressive decrease both in plasma carotene and in vitamin A in human 

 subjects on a completely vitamin A-free diet. The period recjuired for de- 

 pletion is much greater in man, and, after 140 days on the vitamin A- 

 deficient diet, plasma carotene had dropped from 149 to 15 ^tg. %, while 

 blood vitamin A had decreased only from 39.9 to 22.8 ^g- % (133 to 76 

 I.U., respectively). It is thus evident that, in man, plasma vitamin A is 

 much more resistant to change than is plasma carotene. Hartzler*®* 

 showed that it was possible to render the human plasma almost completely 

 free from carotene without evoking any vitamin A-deficiency symptoms. 

 Wald et al.^^^ were also unable to produce a vitamin A-deficiency in any of 

 five men who were maintained on a diet low in vitamin A for six months. 



a'. Vitamin A Tolerance Curves: When standard dosages of vitamin 

 A are given, it is possible to obtain characteristic vitamin A "tolerance" 

 curves which are considered to be of value in assessing the vitamin A status 

 of the subject. 



The nature of the vitamin A tolerance curve varies with the dosage of 

 vitamin A employed, and with other conditions of the test. In the proce- 

 dure used by Krause and Pierce^"^ in testing school children, 7500 or 

 15,000 Mg- (25,000 or 50,000 I.U.) were given in a single dose; maximum 

 blood levels of vitamin A, which were higher when the higher dose of vita- 

 min A was administered, were obtamed in five hours, and the blood pic- 

 ture had returned to practically normal within twenty-four hours. Week 

 and Sevigne^^* obtained comparable results, as regards the time of the oc- 



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



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



