496 V. BLOOD LIPIDS 



ments of Ralli and her co-workers, 880 a second dose of carotene, given dur- 

 ing the interval when hypercarotenemia was still present, was shown to 

 exert a smaller effect on the blood plasma than did the original dose. 

 Wendt 882 carried out feeding tests on human subjects with even higher 

 doses of carotene than those employed by Ralli et al. m After the continued 

 administration of massive doses of carotene, a serum value as high as 1500 

 jug. was noted during the early part of the test; however, this fell to an 

 average maximum value of 490 microgram per cent after four weeks, and no 

 further increase in carotene followed the continued administration of the 

 carotenoid. 882 



Szymanski and Longwell 859 proposed the following prediction formula 

 for plasma carotene, based upon the dietary sources of this provitamin: 



X = 0.46/o + 0.06 I 3 + 86 



in which X is the expected plasma carotene in microgram per cent, h is the 

 average daily intake of vitamin A (carotene) from plant sources in I.U. per 

 kilogram of body weight during the preceding three months, and 7 3 is the 

 average daily intake of vitamin A (carotene) from plant sources in I.U. 

 per kilogram of body weight during the period three to six months prior to 

 the date of the prediction. 



Most of the data available on the effect of ingested carotene on blood 

 carotene are obtained from human subjects, who absorb carotene as such. 

 However, well-controlled tests have been made, by Davis and Madsen, 883 

 on dairy cattle fed carotene-free and vitamin A-free diets and diets con- 

 taining various amounts of carotene. The data are summarized in Table 18. 



In the rat, chick, and guinea pig, which do not absorb carotene as such, 



Table 18 



Levels of Carotene and Vitamin A in the Blood Plasma of Cows 



Receiving Various Amounts of Carotene in Their Diet 



• Adapted from R. E. Davis and L. L. Madsen, J. Nutrition, 21, 135-146 (1941). 



882 H. Wendt, Klin. Wochschr., 14, 9-14 (1935). 



883 R. E. Davis and L. L. Madsen, J. Nutrition, 21, 135-146 (1941 ). 



