470 IX. CAROTENOIDS AND VITAMINS A 



lies ranged between 6 and 52 I.U. Maddock and co-workers^^'' recorded 

 relatively high values for plasma vitamin A for dogs. The figures ranged 

 between 173 and 355 Mg-% (577 and 1183 I.U., respectively); these are 

 higher than those observed under normal conditions in other species. 

 The vitamin A content of the plasma of chickens on a farm diet was 

 reported by Ganguly et al}^ as 82 I.U./IOO ml., while the levels on 

 several diets varied from 55 to 151 I.U. Lewis and collaborators^^" 

 gave 10 to 30Mg./100 ml. (33 to 100 I.U.) as the average range for 

 the vitamin A content of the blood of rats when the vitamin A intake 

 was maintained for six weeks within what is considered to be a nor- 

 mal range. 



c. Factors Altering the Level of Vitamin A. (a) The Effect of Diet. 

 Although the amount of carotene in the ordinary diet has little or no 

 influence upon the level of plasma carotene and of vitamin A,^^^ Getz^"" 

 did find that plasma vitamin A was increased somewhat, along with 

 plasma carotene, when large doses of the provitamin A were given to 

 men. Kimble^^* and Murrill et al}^^ also demonstrated some relation- 

 ship between the increase of plasma vitamin A and plasma carotene 

 after the administration of /3-carotene. Davis and Madsen^''^ cited the 

 following mean values (in itahcs) and range (in parentheses) for plasma 

 vitamin A (expressed in /xg./lOO ml.) in cows which had received dif- 

 ferent amounts of carotene in the diet: "Low diet," 10 (3-16); 30 

 Mg./kg., of body weight (14-21); 45 /xg./kg., 19 (16-23); 60 Mg-Ag., 26 

 (20-31) ; 120 Mg-/kg., 85 (33-36) ; and "High" (pasture), 4d (40-65). 



The administration of vitamin A, either as the ester or as the alcohol, 

 causes a prompt rise in the level of blood vitamin A, which returns to nor- 

 mal shortly after absorption is completed. Ralli and co-workers'^'^ re- 

 corded higher plasma values for vitamin A in male subjects receiving 30,000 

 Mg. of vitamin A (100,000 I.U.) than in those receiving 6000 ^g- (20,000 

 I.U.) during the first twenty-four hours after feeding, but the differences 

 disappeared thereafter. 



In the case of rats, Lewis and collaborators^^" did report a progressive 

 rise in plasma vitamin A which, to some extent, paralleled the intake. 

 Thus, after the following amounts of vitamin A (expressed in )ug- per day) 

 were given to rats for six weeks, the corresponding levels of vitamin A 

 (Mg./lOO ml.) were noted in the plasma: 0, 0; 0.3, 2.1; 0.6, 4.2; 3.0, 

 10.5; 7.5, 20.7; 15, 30.0; 30, 33.6; 300, 33.0; and 30,000, 143.4. The 

 constant level of vitamin A in the blood was not obtained until 15 to 30 

 /ig. were given daily, and this plasma value was maintained when the in- 



3" C. L. Maddock, S. B. Wolbach, and S. Maddock, J. Nutrition, 39, 117-137 (1949). 



