530 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



laid down in the adipose tissues, as well as in the phospholipids. He has 

 also shown that the elaidic acid is apparently utilized, as it gradually dis- 

 appears from the fat stores. 



(c) Linoleic Acid. Linoleic acid, CH 3 (CH 2 ) 4 CH : CHCH 2 CH : CH- 

 (CH 2 )7COOH, is one of the essential fatty acids. It cannot be synthesized 

 in the body, 43 and that present in the fat stores must have been obtained 

 from the diet. When linoleic acid is fed to the pig, large amounts may be 

 retained. 48 - 49 Anderson and Mendel 49 reported that, when 60% of the 

 calories of the diet came from unsaturated fats, the iodine number of the 

 storage fat of rats approximated that of the dietary fat. Even when 

 more saturated fats such as lard or Crisco were fed, there was a selective 

 absorption of the unsaturated acids, so that the body fat was more un- 

 saturated than the dietary fat. 



Although no linoleic acid could be demonstrated in the adipose tissue of 

 the rat on a low-fat diet, Spadola and Ellis 50 were able to detect it in the 

 tissues when it was present in the diet to the extent of only 0.2%. When 

 cottonseed oil was present to the extent of 8% in the diet, linoleic acid 

 made up 27.3% of the component acids. However, under these circum- 

 stances, the amount of palmitoleic acid in the fat was markedly suppressed. 

 When a low-fat diet was employed, palmitoleic acid made up 14.0% of the 

 total fatty acids of the adipose tissue, while linoleic acid was absent. In 

 the test cited above, in which linoleic acid comprised 27.3% of the total 

 fatty acids, the proportion of palmitoleic acid was reduced to 2.0%. 



More recently, Longenecker demonstrated that the storage fat of rats 

 contained 2.2 mole per cent of linoleic acid when a low-fat diet 51 was given, 

 but that this was increased to 18.6 mole per cent on a 5% oil diet, 51 and to 

 32.3 mole per cent on a diet containing a high proportion of corn oil. 52 

 When coconut oil was the dietary fat, 32 the molar percentage of linoleic 

 acid was reduced to 1.2. Ellis and collaborators 53 have shown that, 

 whereas the back fat of the pig contained 8.6% of linoleic acid when a 

 low-fat diet was given, the corresponding amount of linoleate was in- 

 creased to 14.6%, after the ingestion of 4% of cottonseed oil, to 18.6% 

 when 8% of cottonseed oil was included in the diet, and to 26.8% when the 

 diet contained 12% of cottonseed oil. 



(d) Linolenic Acid. Linolenic acid is 9,12,15-octadecatrienoic acid. 



48 N. R. Ellis and O. G. Hankins, /. Biol. Chem., 66, 101-122 (1925). 



49 W. E. Anderson and L. B. Mendel, J. Biol. Chem., 76, 729-747 (1928). 



60 J. M. Spadola and N. R. Ellis, J. Biol. Chem., 113, 205-218 (1936). 



61 H. E. Longenecker, J. Biol. Chem., 128, 645-658 (1939). 



62 H. E. Longenecker, J. Biol. Chem., 129, 13-22 (1939). 



63 N. R. Ellis, C. S. Rothwell, and W. O. Pool, Jr., J. Biol. Chem., 92, 385-398 (1931). 



