CHANGES IN THE GASTROINTESTINAL TRACT 369 



lietweeii the lumen of the gut and the thoracic duct from which the lymph 

 was collected. The intestinal mucosa would seem to be the most logical 

 spot for this transformation. 



3. Changes of Sterols in the Gastrointestinal Tract 



The gastrointestinal tract pro\'ides a site where changes can bo effected 

 in the cholesterol molecule. No profound alterations occur in the upper 

 portion of the tract, other than esterification or hydrolysis; the chief ac- 

 tivity on the cholesterol molecule is confined to the lower part of the 

 gastrointestinal tract, where it is mediated by the bacteria normally present. 

 These transformations may affect the cholesterol which fails to be absorbed, 

 that which is excreted into the gut by way of the bile, or by the intestinal 

 mucosa, and that which is synthesized in the tract.^" According to Burger 

 and Winterseel,^' a considerable amount of ingested cholesterol may be 

 excreted unchanged in the feces. 



Cholesterol may also be dehydrogenated or hydrogenated in the intes- 

 tine. Thus, the conversion of cholesterol to 7-dehydrocholesterol (pro- 

 vitamin D3) by the removal of tw^o hydrogen atoms can occur in the intes- 

 tine of the guinea pig.^^ A common change of cholesterol in the lower gut 

 involves the addition of hydrogen, i.e., a saturation. Thus, Windaus and 

 Uibrig^^ demonstrated that cholestanol (dihydrocholesterol) can be formed 

 from cholesterol in the lower intestinal tract. 



The reaction of the cholesterol molecule which is best known and which 

 has been recognized over the longest period is its conversion to coprostanol. 

 As early as 1862, Austin Flint^'' demonstrated that the cholesterol-like com- 

 pound in feces differed from cholesterol; it was originally called stercorine,''^ 

 but the name koyrosterin assigned to it by Bondzyriski,''* who redisco^^ered 

 it in human feces in 1896, ultimately became the accepted terminology. 

 In line wth the more recent practice, the anglicized form of coprosterin, 

 coprosterol, has been replaced by coprostanol, which indicates that it is a 

 saturated alcohol. There is ample proof that the cholesterol -^ copros- 

 tanol reaction takes place in the gut, since the amount of the latter product 



'» G. Popjdk and M. L. Beeckmans, Biochem. J., 47, 233-238 (1950). 

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

 " M. Glover, J. Glover, and R. A. Morton, Biochem. J., 51, 1-9 (1952). 

 " A. Windaus and C. Uibrig, Ber., 48, 857-863 (1915). 

 7< A. Flint, Am. J. Med. Set., 44, 305-365 (1862). 

 " A. Flint, Z. physiol. Chem., 23, 363-367 (1897). 

 " S. Bondzynski, Ber., 29, 476-478 (1896). 



