366 VIII. CHOLESTEROL AND RELATED STEROLS 



other closely related sterols do not share this property. Thus, Schon- 

 heimer and associates^*"" were the first to demonstrate that plant sterols 

 such as sitosterol and stigmasterol were not absorbed, even when fed along 

 with bile salts. ^* Although Fraser and Gardner^^ originally believed that 

 phytosterols were absorbed and transformed to cholesterol, Gardner and 

 Gainsborough^^ later stated that plant sterols could not be converted to 

 cholesterol in the normal animal. 



More detailed investigation, carried out after the classical experiments 

 of the Schonheimer group were made, reinforced the conclusion that 

 ph3^osterols were incapable of absorption. Thus, a mixture of a, /?, and 

 7-sitosterols were not absorbed by mice, rats, or rabbits.*"'^' Moreover, 

 Rosenheim and Webster^- reported that neither stigmasterol nor /?-sitos- 

 terol (22-dihydrostigmasterol) was absorbed by rats. Sperry and Berg- 

 mann*^ noted that no increase in liver sterols resulted from the feeding of 

 stigmasterol or sitosterol to mice. Similarly, Schonheimer et a/."-^^-*" 

 observed that, not only was sitosterol not absorbed by rabbits and dogs, 

 but also no increase in liver sterols occurred after the feeding of stigmasterol 

 or of brassicasterol to mice. Phjrtosterols do form soluble compounds with 

 bile salts ; however, in spite of the abundance of phytosterols in the human 

 diet, the consensus of opinion has been that they cannot be converted to 

 cholesterol by man. 



However, more recent findings have cast considerable doubt on these con- 

 clusions. Gould and co-workers,**'** using sitosterol labeled with C''* and 

 tritium, in feeding experiments with human subjects and rats, found that 

 this plant sterol was absorbed, although not as eflSciently as was choles- 

 terol. They also observed that the |S-sitosterol was removed from the 

 body considerably more rapidly than was cholesterol, and that no ac- 

 cumulation of this sterol occurred. In later experiments, Gould** deter- 

 mined quantitatively that the absorption of /^-sitosterol in humans and 



«R. Schonheimer, Z. physiol. Chem., 180, 1-5, 16-18, 24-32, 32-37 (1929); 185, 

 119-122(1929). 



^« R. Schonheimer and D. Yuasa, Z. physiol. Chem., 180, 5-16, 19-23 (1929). 



« H. V. Behring and R. Schonheimer, Z. physiol. Chem., 192, 97-102 (1930). 



*8 R. Schonheimer, H. v. Behring, and R. Hummel, Z. physiol. Chem., 192, 117-123 

 (1930). 



" J. A. Gardner and H. Gainsborough, Quart. J. Med., 23, 465-483 (1930). 



so R. Schonheimer, Klin. Wochschr., 11, 1793-1796 (1932). 



" F. L. Breusch, /. Biol. Chem., 124, 151-158 (1938). 



" O. Rosenheim and T. Webster, Biochem. J., 35, 928-931 (1941). 



" W. M. Sperry and W. Bergmann, J. Biol. Chem., 119, 171-176 (1937). 



" R. G. Gould, Circulation, 10, 589 (1954). 



« R. G. Gould, L. V. Lotz, and E. M. Lilly, Federation Proc, U, 487 (1955). 



66 R. G. Gould, Trans. New York Acad. Sci., ser. II, 18, 129-134 (1955). 



" R. P. Cook, Ninety-seventh Meeting Nutrition Soc. (Brit.), Aberdeen, Sept., 1955; 

 Proc. Nutrition Soc, 15, no. 1, 41-45 (1956). 



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