ABSORPTION .VXD TRANSPORT 363 



likewise confirmed the fact that an increased level of cholesterol obtains in 

 the blood, irrespective of whether it is fed as the alcohol or as the ester; 

 however, cholesterol esters were shown to be hydrolyzed before being ab- 

 sorbed. According to Mueller," the cholesterol content of the chyle is like- 

 wise increased after the administration of this sterol. The proportion of 

 free to esterified cholesterol is similar in chyle to that of blood; moreover, 

 it remains constant, irrespective of whether the steroid is administered in 

 free or in esterified form. These data are in harmony with the evidence 

 that a cholesterol esterase system is present in the intestinal wall which 

 can mediate both hydrolysis and esterification.-'*'-^ 



(1) Factors Altering Cholesterol Absorption 



A number of factors alter the absorption of cholesterol from the gastro- 

 intestinal tract. Thus, the presence of fat in the diet increases the effi- 

 ciency of absorption of cholesterol from the gut, although this effect may 

 vary with species. Some animals, as for example rabbits, absorb choles- 

 terol readily in the absence of fat, while chickens, rats, and guinea pigs 

 carry out this function less readily on fat-free diets. 



Dam et alr^ fed young chicks a commercial diet to which cholesterol dis- 

 solved in 10% peanut oil was added. After fourteen days of this feeding, 

 no significant increase in the cholesterol was noted in the li\'er, spleen, 

 aorta, and bile when the cholesterol content of the diet was from to 1% 

 of the ration, but a marked increase occurred in the range between 0.1 

 and 0.33%, and at higher levels. WTien the cholesterol was given without 

 fat, the increase in the organs was much less, except in the case of the liver; 

 in this organ the cholesterol values corresponding to and 0.1% of dietary 

 cholesterol were significantly higher on the fat -free diet than on that con- 

 taining 10% peanut oil. This agrees with the findings of Alfin-Slater and 

 co-workers," who fomid liigher values in the livers of rats on fat-free diets 

 than in those of animals fed diets containing 15% of cottonseed oil. 



A second important factor in stimulating the absorption of cholesterol is 

 the presence of bile salts. Schonheimer-^ demonstrated that an optically 

 \'isible lipemia could be produced in rabbits when they were fed a single 



" J. H. Mueller, /. Biol. Chem., 22, 1-9 (1915); 27, 463-480 (1916). 

 2< E. Frohlicher and H. Siillmann, Biochem. Z., 274, 21-33 (1934). 

 « M. L. Xieft and H. J. Deuel, Jr., J. Biol. Chem., 177, 143-150 (1949). 

 2« H. Dam, I. Prange, and E. S0ndergaard, Acta Physiol. Scand., 34, 141-146 (1955). 

 " R. B. Alfin-Slater, L. Mtergood, A. F. Wells, and H. J. Deuel, Jr., Federation Proc, 

 13, 174(1954). 



28 R. Schonheimer, Biochem. Z., 147, 258-263 (1924). 



