398 VIII. CHOLESTEROL AND RELATED STEROLS 



fact that the total quantity synthesized by the latter endocrine gland is in- 

 significant compared with that manufactured in the liver. Gould et al.^^^ 

 reported that the rate of synthesis of endogenous cholesterol in the skin and 

 intestinal mucosa was not influenced by exogenous cholesterol; this is in 

 sharp contrast to the effect of cholesterol feeding on the liver. 



Popjak and Beeckmans^" proved that cholesterol synthesis occurred in 

 the rabbit, not only in the liver but also in the intestine and ovaries. The 

 rate of synthesis of cholesterol w^as found to be higher in the rabbit fetus 

 than in maternal tissues;"^ the fetal livers were especially active In choles- 

 terol production, while the extrahepatic tissues of the fetus were more ac- 

 tive in fatty acid synthesis. In a later study, Popjak and Beeckmans"^ 

 demonstrated that all fetal cholesterol is obtained by synthesis within the 

 body of the fetus. It w^as f oimd that fetal extrahepatic tissues had the ca- 

 pacity to sjaithesize cholesterol, but that they were unable to degrade it. 

 Only the fetal liver was able both to synthesize and to destroy cholesterol. 

 The amount of cholesterol destruction amounted to only 50% of that 

 synthesized, on the twenty-eighth day of pregnancy. 



The ovarian tissues of the laying hen are likewise important sites for 

 cholesterol S3aithesis. Thus, Popjak and Tietz"^ found that the mem- 

 branes surrounding the gro\\dng ovum, which consist of the theca interna 

 and theca granulosa, synthesize cholesterol as well as fatty acids in vitro 

 from acetate. On the other hand, the yolk and the germinal disk possess 

 no such capacity for s>Tithesis. Although the theca interna and theca 

 granulosa were inferior to the liver sHces of young rats in effecting a syn- 

 thesis of fatty acids from acetate, they were found to be as active as hepatic 

 tissue in the synthesis of cholesterol. Kritchevsky and associates^^^-^" 

 reported that carboxyl-labeled acetate, when fed to laying hens, rapidly 

 appeared in the cholesterol fraction and other fractions of the egg; how- 

 ever, the highest specific acti\aty of the isotopic carbon was found in the 

 cholesterol. Rice and her collaborators"* described the preparation of 

 deuterium-labeled cholesterol from egg yolks by feeding deuterium oxide 

 and/or deuterium-labeled sodium acetate to lajdng hens. The sjmthesis 

 of cholesterol from carboxyl-labeled sodium acetate in the fertile hen's egg 



"3 G. Popjdk and M. L. Beeckmans, Biochem. J., 44, x.xxvi-xxxvii (1949). 



"^ G. Popjdk and M. L. Beeckmans, Biochem. J., 46, 547-558 (1950). 



!"5 G. Popjdk and A. Tietz, Biochem. J., 5Jf, xxxv (1953). 



276 D. Kritchevsky, C. R. Grau, B. M. Tolbert, and B. J. Krueckel, Proc. Sac. Exptl. 

 Biol. Med., 76, 741-743 (1951). 



2" D. Kritchevsky and M. R. Kirk, Proc. Soc. Exptl. Biol. Med., 78, 200-202 (1951). 



"8 L. I. Rice, R. B. Alfin-Slater, and H. J. Deuel, Jr., Proc. Soc. Exptl. Biol. Med., 80, 

 562-563 (1952). 



