270 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



any deposition of ergosterol in rats, rabbits, mice, and dogs, after feed- 

 ing this sterol to the animals over long periods of time, Page and Men- 

 schick 128 recorded some absorption of this sterol. These latter results 

 were confirmed by Hanahan and Wakil 129 who found that 2 to 5% of 

 orally administered C 14 -ergosterol was absorbed within six hours, mainly 

 through the lymph system. On the other hand, the evidence is more 

 clearcut that ergosterol (provitamin D 2 ) when given in large amounts, can 

 be absorbed by laying hens. 130,131 However, Bloor 87 reported that 

 ergosterol could not be absorbed unless it had previously been irradiated 

 (and presumably changed to vitamin D 2 ) . 



Isocholesterol, which is obtained from lanolin, and which has long been 

 considered to be a C3o-sterol, is likewise nonabsorbable. 113 However, it is 

 now recognized that agnosterol and lanosterol, of which isocholesterol is 

 mainly composed, belong to the group of triterpenes rather than to that of 

 the steroids. 



It should be apparent from the above experiments that a selective ab- 

 sorption of the sterols obtains in the gastrointestinal tract; these data 

 suggest that extremely small differences in molecular structure can largely 

 determine the fate of a sterol. One possible explanation for the difference 

 between cholesterol and the other sterols is the fact that the latter can 

 apparently not be esterified after subcutaneous injection 111 ; on the other 

 hand, cholesterol is quickly esterified following subcutaneous administra- 

 tion. If a similar discrepancy in behavior between these two types of 

 sterols also obtains in the intestinal mucosa, it is possible that this could 

 account for the failure of the phytosterols and of other cholesterol esters 

 to be absorbed. 



(S) The Effect of Plant Sterols on the Absorption of Cholesterol 



Although the experimental data are almost unanimous in indicating 

 that the phytosterols are inert insofar as their absorption from the gastro- 

 intestinal tract is concerned, it has been suggested that the presence of 

 these substances in the diet may influence the absorption of cholesterol 

 from the small intestine. Peterson 132 was the first to show that, when 

 soybean sterols were fed to chicks together with cholesterol, hyperchole- 

 sterolemia was prevented, and the deposition of cholesterol in the fiver 



128 1. H. Page and W. Menschick, Biochem. Z., 221, 6-10 (1930). 



129 D. J. Hanahan and S. J. Wakil, Arch. Biochem. Biophys., U, 150-158 (1953). 



130 R. Schonheimer and H. Dam, Z. physiol. Chem., 211, 241-245 (1932). 



131 W. Menschick and I. H. Page, Z. physiol Chem., 211, 246-252 (1932). 



132 D. W. Peterson, Proc. Soc. Exptl Biol Med., 78, 143-147 (1951). 



