CHAPTER VIII 



THE METABOLISM OF CHOLESTEROL 



AND RELATED STEROLS IN THE 



ANIMAL BODY 



1. Introduction 



Because of the wide distribution of sterols in the tissues, and their im- 

 portant physiologic properties, these compounds constitute an especially 

 interesting category of lipids. Although cholesterol itself cannot be re- 

 garded as the most striking member of this group on the basis of its physio- 

 logic action, this sterol must be considered as the key constituent, both be- 

 cause of its exceedingly wide distribution in the animal body and also be- 

 cause of its obvious significance as the parent substance of many of the 

 steroid hormones. The metabolism of cholesterol will be considered in 

 this chapter, from the standpoints of the absorption and transport of exog- 

 enous cholesterol, the biosynthesis of endogenous cholesterol, and the 

 intermediary transformation of cholesterol, together with a consideration 

 of the nature of the products originating from cholesterol, and finally from 

 the viewpoint of the ultimate disposal of the sterol nucleus. 



The discovery of cholesterol as an entity is one which dates back to 1769, 

 when Poulletier de la Salle ^ first prepared it from gallstones; it was shown 

 to be a component of the nonsaponifiable residue, by Chevreul- in 1815. 

 However, the modern understanding of it began with the demonstration of 

 its alcoholic nature by Berthelot.' 



The actual conception of the metabolism of cholesterol and of its inter- 

 relationship with the steroid hormones has been a development of the past 

 two decades. This advance in knowledge was impossible until the struc- 

 ture of cholesterol was completely elucidated. Although Reinitzer^ had 



1 Poulletier de la Salle, circa 1769; cited bv de Fourcrov, Ann. chim. phys. [1], 

 3, 2-12-252 (1789) and by C. E. Bills, Physiol. Revs., 15, 1-97 (f935). 



2 M. E. Chevreul, Ann. chim. phys. [1], 95, 5-50 (1815). 

 » M. Berthelot, Ann. chim. phys. [3], 56, 51-98 (1859). 



* F. Reinitzer, Monatsh., 9, 421-441 (1888). 



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