LIPIDS PRESENT IN LIVER 715 



discussion of the glyceryl ethers, the reader is referred to Volume I, pages 

 392-396. 



{2) Physiologic Factors Altering the Lipid Composition 

 of Normal Livers 



a. The Effect of Age on Liver Lipids. In studies of guinea pigs, Imrie 

 and Graham 70 found that the level of liver lipid of the embryo pigs approxi- 

 mated the value found in the liver of the mother, i.e., 2 to 3%. After the 

 fetuses had reached a weight of 35 to 40 g., a rapid increase in liver lipids 

 obtained, until the maximum figure of 16 to 18% was reached at birth. 

 The excess fat stored in the livers was rapidly used in the first two or three 

 days of life. Lang 71 reported a higher level of liver lipid in the rat fetus 

 and in young animals than in the adult animal ; the human fetus and new- 

 born, also, have been shown to contain more fat than is present in the liver 

 and other organs after birth. 72 Dimter 73 also found that the cholesterol 

 content of the fetal liver of the horse, cattle, and man was higher than that 

 of the adult organ. On the other hand, the non-cholesterol component of 

 the non-saponifiable fraction of the liver was much higher in the adult 

 animal. 



Lang 71 found that, in growing rats concerning which data were available 

 from birth to maturity, the liver phospholipid was approximately constant. 

 On the other hand, liver cholesterol increased to a maximum at the age of 

 fifteen days, after which it again decreased. The decrease was attributed 

 to the rapid growth period beginning at twenty days. 



Williams et al. 7i reported that the total liver lipids of rats fifteen days old 

 amounted to 19.85% of the dry weight; the essential lipids totaled 13.50% 

 on an average, while the balance of 6.35% consisted of neutral fat. The 

 percentages of the essential lipids based upon the dry weight of the liver 

 of the fifteen-day rat were as follows : phospholipids, 1 1.67% ; cerebrosides, 

 0.12%; cholesterol esters, 1.44%; and free cholesterol, 0.27%. At the age 

 of seventy days, there was a slight decrease in neutral fat to 5.22%, and 

 somewhat of an increase in essential lipids to 14.98%. The principal 

 changes in the individual products were a marked increase in phospholipid 

 coupled with a concomitant reduction of the cholesterol esters. 



70 C. G. Imrie and S. G. Graham, /. Biol. Chem., 41, xlviii-xlix (1920). 



71 A. Lang, Z. physiol. Chem., 246, 219-223 (1937). 



72 L. Aschoff, Zentr. allgem. Pathol, u. pathol. Anat., 8, 861-862 (1897). 



73 A. Dimter, Z. physiol. Chem., 271, 293-315 (1941). 



74 H. H. Williams, H. Galbraith, M. Kaucher, E. Z. Mover, A. J. Richards, and I. G. 

 Macy, /. Biol. Chem., 161, 475-484 (1945). 



