PRODUCTS RELATED TO CHOLESTEROL 417 



there aii}^ evidence of sitosterol storage. ^'^"'^^^ A number of phytosterols 

 have been shown to inhibit cholesterol absorption from the small intestine 

 of the rat.^^ According to Bisset and Cook,^*^^ and to other workers," -^^^"^^^ 

 sitosterol inhibits the esterification of cholesterol in the intestine of human 

 subjects as well, and reduces the amount of this sterol in the blood. It is 

 suggested by Davis^^"^ that ingested /3-sitosterol reduces the dispersibility 

 of cholesterol by colloidal dispersing agents in the intestine and thus re- 

 duces its absorption. 



(3) t3-Cholestanol (Dihydrocholesterol) 



In addition to coprostanol (coprosterol), a second saturated Coy steroid 

 occurs in feces. In contradistinction to coprostanol, which originates in 

 the gut and which does not occur in the tissues, /3-cholestanol is present in 

 the tissues, and it is apparently excreted into the gut to be eliminated in 

 the feces. 



According to Schoenheimer, as cited by Bills, ^ j8-cholestanol is present to 

 the extent of 2% or 3% in the tissue sterols. It has been postulated that 

 the j8-cholestanol must originate by saturation of cholesterol in situ, since 

 it has been proved that it cannot be absorbed. Schoenheimer^^ postulated 

 that a hydrogenation-dehydrogenation reaction occurs whereby jS-choles- 

 tanol is formed simultaneously with the dehydrogenation of another mole- 

 cule to ergosterol. It is now recognized that this reaction is impossible, 

 inasmuch as ergosterol is kno^\^l to have twenty-eight carbons, while 

 cholesterol has only twenty-seven carbons. 



/3-Cholestanol is probably not excreted via the bile, since gallstone choles- 

 terol has been found to have a very small content of this sterol. ^^ Schon- 

 heimer and Hrdina^^^ noted the absence of any sterols in the gastric and 

 pancreatic secretions of dogs, but they did observe that the intestinal juice 

 contained both cholesterol and /3-cholestanol. The secretion of /3-choles- 

 tanol by this route was verified by Schonheimer and v. Behring,^" who iso- 

 lated the lower gut of dogs and found that the sterile masses of intestinal 

 secretion which accumulated after one or two months contained very sig- 

 nificant amounts of jS-cholestanol, but no coprosterol or cholesterol. Similar 



^^5 R. Schonheimer, H. v. Behring, R . Hummel, and L. Schindel, Z. physiol. Chem., 192, 

 73-76(1930). 



3^6 S. K. Bisset and R. P. Cook, 350th Meeting, Biochem. Soc, Glasgow, April, 1956. 



3" R. E. Shipley, Trans. New York Acad. Set. [2], 18, 111-118 (1955). 



'^* C. F. Wilkinson, Jr., R. S. Jackson, R. C. Bozian, M. R. Benjamin, A. H. Levere, 

 G. Craft, and X. W. Davidson, Trans. New York Acad. Sci. [2], 18, 119-122 (1955). 



369 Anonvmous, Nutrition Revs., 14, 39-41 (1956). 



"0 W. W. Davis, Trans. New York Acad. Sci. [2], 18, 123-128 (1955). 



