TRIGLYCERIDES AND FATTY ACIDS 191 



fact, the more highly imsaturated neutral fat appears to be confined largely 

 to the liver.*" 



There is some question as to whether the hepatic lipids have high iodine 

 values because they are desaturated in situ or whether this results from a 

 selection of the highly unsaturated fatty acids from those brought to the 

 liver by the blood stream for retention by this organ. The concept of 

 Leathes and his co-workers ^^~^^ that the liver desaturates fat as the pre- 

 liminary step in its oxidation has not been adequately proved. When cod- 

 liver oil was fed, the liver fat contained fatty acids wdth a higher iodine 

 number than was the case on the basal diet, both in the case of rats^^ and 

 in the case of dogs.*^^ On the other hand, Sinclair *^^ found that, although 

 the administration of cod-liver oil to cast resulted in increased unsatura- 

 tion in the phospholipid fraction of the liver, the iodine values did not 

 exceed that of the cod-liver oil fed. Leathes and Meyer- Wedell^^ inter- 

 preted their results as indicating a desaturation by the liver, while Joanno- 

 \'ics and Pick*^^ considered that the liver selected the more highly mi- 

 saturated acids furnished in the diet and carried them to the liver for reten- 

 tion. Imrie*^" is of the opinion that the liver is the only organ which can 

 cause any considerable degree of desaturation of the fatty acids. 



However, a number of facts are opposed to the concept that the liver has 

 an especial capacity for desaturation of the fatty acids. Thus, Klenk and 

 V. Schoenebeck**^ found that the high degree of unsaturation of liver 

 lipids was not due to Cis acids which had been desaturated, but rather to a 

 C22-tetraenoic acid (arachidonic acid). Since it is kno\ATi that arachidonic 

 acid cannot be synthesized in the animal body,*^* it is evident that the 

 increased unsaturation of the liver lipids is not due to in vivo synthesis. 

 In fact, Burr*^* proved that the liver is unable to synthesize a dienoic acid 

 such as lin oleic acid. Moreover, McMaster and Drury**^ reported that 

 90% of the liver could be removed without altering the R.Q. of fasting 

 rabbits; this was interpreted to mean that the liver does not carry out any 

 unique function in fat catabolism. 



Finally, although Bloor*-^ is of the opinion that desaturation is a normal 

 stage in the oxidation of the fatty acids, the dehydrogenation occurs from 

 the carboxyl end of the fatty acid, and not in the middle. Although 

 Schoenheimer and Rittenberg^"* proved, by the use of deuterium-labeled 

 saturated fatty acids, that desaturation occurs in the animal, it is uncertain 



«9 G. Joannovics and E. P. Pick, Wien. klin. Wochschr., 23, 573-577 (1910). 



6«oC. G. Imrie, J. Pathol. BaderioL, 10, 245-257 (1914). 



««• E. Klenk and O. v. Schoeneberk, Z. physiol. Chem., 209, 112-133 (1932). 



6" p. D. McxMaster and D. R. Drury, Proc. Soc. Exptl. Biol. Med., 25, 151-153 (1927). 



