INTERMEDIARY METABOLISM OF CHOLESTEROL 411 



still present in the serum forty-eight hours after intravenous injection, and 

 32% could be recovered in the sterols isolated from the lungs, liver, spleen, 

 adrenals, and serum after this interval, no significant radioactivity could 

 be found in the sterols of the serum or of the organs at the end of forty-eight 

 hours after 7-keto- or 7-hydroxycholesterol had been injected. Although 

 the metabolic disposition of the 7-oxygenated sterols is still not understood, 

 the possibility exists that they may be intermediates in the oxidative deg- 

 radation of cholesterol in the body.^*' A number of years earlier, after 

 making a careful examination of yeast fat, acorn fat, wheat germ oil, and 

 saponified cholesterol stearate, Haslewood^*^ proved that no 7-hydroxy- 

 sterols could be detected. It is suggested that, when 7-hydroxysterols are 

 present, they represent true intermediates in cholesterol metabolism rather 

 than substances formed during the isolation procedures. 



{10) Hydrogenation of Cholesterol 

 in the Gastrointestinal Tract 



In addition to dehydrogenation, hydrogenation can likewise be carried 

 out in the gastrointestinal tract. The hydrogenation of cholesterol may 

 involve its transformation into coprostanol (formerly called coprosterol), 

 epicoprostanol, and cholestanol (formerly called dihydrocholesterol) . 

 The change of cholesterol -* coprostanol does not merely involve a reduc- 

 tion to cholestanol, but requires a pathway via cholestenone, coprostenone, 

 and coprostanol. The presence of cholestenone as an intermediate was 

 proved by Rosenheim and Webster,-^ who identified it by its ultraviolet 

 absorption, and prepared cholestenone-o-tolylsemicarbazone from the 

 feces of the dog and rat after feeding brain as the source of cholesterol. 

 This pathway is further substantiated by Marker et a/.,^^^ who succeeded 

 in isolating epicoprostanol from the feces of a dog; this compound must 

 have originated from cholestenone. It has been proved that labeled co- 

 prostanone is excreted as coprostanol.^^ The transformation of choles- 

 terol to coprostanol is discussed earlier in this present chapter (pages 

 369-370), as well as on pages 271-274 of Vol. II, The Lipids. 



A second hydrogenation which can take place is the change, cholesterol 

 -* cholestanol. The latter compound is excreted in the feces ;^^ it cannot be 

 absorbed from the intestine. ^'^-^''^ 



s« G. A. D. Haslewood, Biochetn. J., 36, 389-391 (1942). 



"* R. E. Marker, E. L. Wittbecker, R. B. Wagner, and D. L. Turner, /. .4m. Chem. 

 Soc, 64, 818-822 (1942). 



3« R. Schonheimer and L. Hrdina, Z. physiol. Chem., 212, 161-172 (1932). 



