260 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



(a) The Effect of Fat on Cholesterol Absorption. The absorption of 

 cholesterol from the small intestine apparently takes place most efficiently 

 if it is given with fat, 67,68 although Bollman and Flock 69 agreed with the 

 findings of Dubach and Hill, 70 who were able to demonstrate an increase in 

 the level of plasma cholesterol after feeding the sterol without an oil carrier. 



Apparently the requirement for fat to insure cholesterol absorption varies 

 with species. On the one hand, Cook 71 reported that, if rats are fed a diet 

 relatively free from lipid but containing cholesterol, the sterol can be re- 

 covered quantitatively from the feces. On the other hand, Popjak 72 noted 

 that guinea pigs and rabbits on a low-fat diet were able to absorb small 

 amounts of cholesterol when it was given in a finely divided aqueous sus- 

 pension. Cook and Thomson 73 found that, while rats and guinea pigs 

 absorbed 46 to 50% of the cholesterol on a diet containing 16.6% of olive 

 oil, rabbits utilized 82% of the sterol. Thus, the more ready absorption of 

 cholesterol by the rabbit is not solely dependent upon the presence of fat 

 in the diet. However, Frolicher and Siillmann 66 demonstrated that the con- 

 tent of free cholesterol in the intestinal ljonph of rabbits is increased when 

 fat is given; they attribute this phenomenon to a reabsorption of excreted 

 cholesterol. Kim and Ivy 74 likewise reported that the presence of fat in 

 the diet of rats may facilitate the absorption of exogenous cholesterol. 



In the case of chickens, although hypercholesteremia developed to some 

 extent when cholesterol was incorporated into a fat-free diet to the extent 

 of 2% (Stamler and Katz), 75 or 1% (Peterson et al.),™ a much greater de- 

 gree of cholesteremia occurred when extra fat was fed with the diet, thus 

 indicating that fat facilitates cholesterol absorption in the chick as well. 

 It is suggested by Peterson el al. 76 that this effect of fat in augmenting 

 cholesterol absorption may be associated with its action in increasing bile 

 flow. 



(6) The Effect of Bile on Cholesterol Absorption. Bile salts are an even 

 more important factor in stimulating the absorption of cholesterol than 

 is the solvent action of fat. Although the normal bile secretion may be 



67 S. J. Tharmhauser, Beat. Arch. klin. Med., 141, 290-311 (1923). 



68 M. Sano, Tohoku J. Exptl. Med., 4, 417-425 (1924). 



69 J. L. Bollman and E. V. Flock, Am. J. Physiol, 164, 480-485 (1951). 



70 R. Dubach and R. M. Hill, J. Biol. Chem., 165, 521-531 (1946). 



71 R. P. Cook, Biochem. J., 30, 1630-1636 (1936). 



72 G. Popjak, Biochem. J., 40, 608-621 (1946). 



73 R. P. Cook and R. O. Thomson, Biochem. J., 44, li (1949). 



74 K. S. Kim and A. C. Ivy, Am. J. Physiol, 171, 302-318 (1952). 



75 J. Stamler and L. N. Katz, Circulation, 4, 255-261 (1951). 



76 D. W. Peterson, E. A. Shneour, N. F. Peek, ami H. W. Gaffey, J\ Nutrition, 50, 

 191-201 (1953). 



