716 VII. LIPID DISTRIBUTION IN SPECIFIC TISSUES 



Age may be an important consideration in the determination of the level 

 of polyunsaturated acids in the liver. Klein and Johnson 75 noted that no 

 change obtained in the level of dienoic, trienoic, tetraenoic, and pentaenoic 

 acid content in three cytoplasmic particulate fractions of the livers of old 

 rats maintained on a diet considered to be adequate with respect to the 

 essential fatty acids. However, there was a marked decrease in the level 

 of pentaenoic acid, concurrently with an increase in trienoic acid in the 

 liver fractions of old rats raised on a diet which had an inadequate essential 

 fatty acid content. 



The concentration of vitamin A is considerably lower in the fetal liver, as 

 well as in fetal plasma, than it is in the liver and plasma of the mother. 76 " -84 

 Williamson 82 reported that, when 2.5 to 5% of cholesterol was incorporated 

 in the diet of pregnant rats, the lipid content of the placenta was increased 

 over that of the controls. However, the fetuses from such cholesterol-fed 

 mothers contained significantly less vitamin A than was present in the ma- 

 ternal organism. This led to the conclusion that the placenta inhibits the 

 transfer of vitamin A from the maternal to the fetal organism. 



b. The Effect of Sex on Liver Lipids. Although the sex variation in 

 lipid metabolism is a generalized phenomenon, the clearest expression of 

 this variation is to be noted in the lipid composition of the liver. Higher 

 liver glycogen values occur in male rats than in female rats, while the 

 opposite obtains insofar as lipids are concerned. Moreover, the extent of 

 the ketonuria produced by fasting is much greater in women than in men, 

 and the same relationship is true in the case of endogenous ketonuria in the 

 rat. Likewise, fasting female rats excrete much higher amounts of the 

 ketone bodies when ketogenic acids are fed to them than do male rats. 



c. The Effect of Fasting on Liver Lipids. Since the liver is the principal 

 organ involved in the degradation of fats, as well as of most other lipids, it 

 is only natural that the lipid content of this organ should rise during 

 starvation, when the maximum energy is being engendered by the combus- 

 tion of fats. This situation also obtains in rats and mice 85 when they are 

 given carbohydrate-free diets. 



76 P. D. Klein and R. M. Johnson, Arch. Biochem. Biophys., 48, 172-177 (1954). 



76 W. J. Dann, Biochem. J., 26, 1072-1080 (1932). 



77 W. J. Dann, Biochem. J., 28, 634-637 (1934). 



78 W. Neuwiler, Z. Vitaminforsch., IS, 275-280 (1943). 



79 G. H. Wise, M. J. Caldwell, and J. S. Hughes, Science, 103, 616-618 (1946). 



80 C. J. Lund and M. S. Kimble, Am. J. Obstet. Gynecol., 46, 207-221 (1943). 



81 L. Portes and J. Varangot, Compt. rend. soc. biol, 136, 166-168 (1942). 



82 M. B. Williamson, J. Biol. Chem., 174, 631-636 (1948). 



83 J. B. Ellison and T. Moore, /. Soc. Chem. Ind., 55, 236 (1936). 



84 J. B. Ellison and T. Moore, Biochem. J., 31, 165-171 (1937). 



85 A. Hynd and D. L. Rotter, Biochem. J., 24, 1390-1399 (1930). 



