266 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



intestinal bacteria or protozoa are responsible for the conversion of chole- 

 sterol to coprosterol; Schoenheimer and Breusch 93 are of the same opinion. 

 However, in the experiments of Wainfan and collaborators, 100 it was 

 demonstrated that, in mice fed on a diet containing 1.5% of cholesterol, 

 an average of approximately 12% of the administered sterol was either 

 destroyed or chemically modified. That this deficit is to be ascribed to 

 bacterial action in the gut is strongly indicated by the fact that a com- 

 plete recovery of ingested cholesterol obtained when 1% sulfasuxidine 

 and 0.04% streptomycin were added to the diet. Although the synthesis 

 of cholesterol with its resultant excretion into the intestine might com- 

 pensate for some of the cholesterol destroyed, the experiments of Wainfan 

 and her associates involved the use of much larger amounts than the 

 physiological quantities. 



Unquestionably cholesterol can be absorbed when bile salts are present; 

 the absorption is probably aided when fat is likewise available. However, 

 the ability of the animal to absorb cholesterol is limited; if the quantities 

 of the sterol are appreciable, then invariably some of it fails to be absorbed. 

 The quantity of sterol in the intestine is augmented by that contributed 

 by the bile, as well as by that secreted by the intestinal mucosa. 



Most of the cholesterol undergoes a transformation to cholestanol 

 (dihydrocholesterol) or coprostanol (coprosterol), which are the chief 

 sterols in the feces. However, Schoenheimer 101 has devised an analytical 

 procedure for the separation of unsaturated from saturated sterols which 

 is sufficiently precise as to render possible the isolation and identification 

 of cholesterol in human feces. The various transformations of the sterols 

 in the intestinal tract are discussed on pages 271-274. 



(a) Balance Experiments in Man. Gardner and Fox 102 reported that, 

 with low intakes of cholesterol, more was excreted in the feces than was 

 ingested. On the other hand, when large amounts of this alcohol were 

 fed, considerable absorption of the sterol took place. Thus, Burger and 

 Winterseel 103 observed absorption of 50%, 49%, and 12% of cholesterol 

 when 5 g. was fed with 100 g. of olive oil on a mixed diet to three subjects. 

 When a milk diet was given, the digestibility coefficient was found to be 63. 

 Cook and Edwards 104 reported an absorption of 20% when 10 g. of crystal- 



89 O. Rosenheim and T. A. Webster, Biochem. J., 37, 580-585 (1943). 



100 E. Wainfan, G. Henkin, I. Rice, and W. Marx, Arch. Biochem. Biophys., 38, 187- 

 193(1952). 



101 R. Schoenheimer, J. Biol. Chem., 105, 355-357 (1934). 



102 J. A. Gardner and F. W. Fox, Proc. Roy. Soc. London, B92, 358-367 (1921). 

 108 M. Burger and W. Winterseel, Z. physiol Chem., 181, 255-263 (1929). 



104 R, P. Cook and D. C. Edwards, Biochem, J., 49, xli (1951). 



