GENERAL CONSIDERATIONS 419 



8. General Considerations Related to Cholesterol and to the 



Sterols in General 



(1) Functions of Cholesterol 



The widespread distribution of cholesterol in nature must be an indica- 

 tion of its importance in the hfe processes. In the extensive investigations 

 of Doree'^^ on the distribution of cholesterol in the animal kingdom, this 

 sterol was present in all species except the red starfish, or "five-finger" 

 (Asterias ruhens), which contained a closely related complex alcohol. If 

 it were not of primary importance, it would certainly be lacking in some 

 animals. Although cholesterol has important functions, Shope^*'' stated, 

 as recently as 1928, that there is a "complete absence of knowledge con- 

 cerning the function of cholesterol itself." However, Bills^ Hsted a number 

 of f mictions attributable to cholesterol, and to other sterols. For example, 

 they may exert a conditioning action on skin, hair, and feathers. Choles- 

 terol is thought to act as a conveyer in the absorption of fats. Bloor^^ 

 reported a parallelism between the cholesterol content of blood and the 

 fatty acid content. It is suggested by Minovici^^^ and by Lovern^^^ that, 

 in view of the abmidance of cholesterol in brain and nerves, and its varia- 

 tion in mental disease, it may function as an insulating medium for the 

 myehn sheaths. Sterols are thought to have a role in maintaining the bal- 

 ance between cell permeability and the membrane equilibrium of Uving 

 cells. The presence of sterols in seeds, pollen, spores, ova, and sperm cells 

 may indicate a need for these substances by the developing embryo. 



According to Lovern^^® a correlation exists between the hpid content of 

 tissues and their functional acti^^ty. Higher levels of phospholipid -\- 

 cholesterol appear to be associated with greater functional activity. For 

 example, slowly-fatiguing muscle tissue such as heart muscle has the high- 

 est cholesterol content. ^^- 



The possible role of sterols as detoxicating agents has been suggested, 

 although the evidence is still presumptive.^ Abderhalden and Le Count ^^^ 

 found that cholesterol, but not its esters, counteracted the lytic action of 

 saponin, solanin, cobra venom, and tetanus toxin. According to Mino- 

 vici,^^^ numerous hemolytic agents, including venoms, saponins, bacterial 

 toxins, bile salts, soaps, hexylresorcinol, etc., are neutralized by sterols. 



"9 C. Dor6e, Biochem. J., 4, 72-106 (1909). 



3s» R. E. Shope, /. Biol. Chem., 80, 127-132 (1928). 



^1 S. Minovici, Bull soc. chim. hioL, 9, 1129-1164 (1927). 



^2 G. Embden and H. Lawaczeck, Z. phijsiol. Chem., 125, 199-209 (1923). 



^3 E. Abderhalden and E. R. Le Count, Z. exptl. Pathol. Therap., 2, 199-215 (1906) 



