TRIGLYCERIDES AND FATTY ACIDS 195 



creatized dogs,^^^ and after hepatectomy in rabbits"'*^ have been interpreted 

 as proving extrahepatic oxidation of fats. Typical figures for the utihza- 

 tion of fat were Ukewise noted in heart-hmg prcparations,^^^'^^^ provided 

 carbohych'ate was not prc^sent in the pei'fusing fluid. Roberts et alJ''^ 

 found that eviscerated animals, previously maintained on carbohydrate- 

 free diets, subsisted on fat, sparing blood glucose, and that no ketone bodies 

 accumulated in the blood or tissues. 



In subsequent experiments, in which the fats were labeled with iso- 

 topes, more extensive information was obtained as to the site of fat utiliza- 

 tion. For example, Wehihouse, Millington, and Volk®*^ demonstrated that 

 the oxidation of palmitic acid is brought about by a series of extrahepatic 

 tissues, including homogenized pigeon breast muscle and heart, rat heart, 

 and rat kidney. Rat skeletal muscle and l)rain were found to be inactive in 

 fat oxidation. In later studies,^^^ it was fomid by the use of labeled 

 palmitate that a metabolicallj^ acti\'e fatty acid fragment occurs which is 

 not in immediate equilibrium with the tissue lipids. Lehninger"^ likewise 

 demonstrated that palmitic and octanoic acids could be metabolized by 

 heart muscle, and subsequently incorporated into succinate and keto- 

 glutarate. 



Geyer and co-workers^^^-^^^ reported differences in the oxidation pattern 

 of C^Mabled octanoic acid in liver and in kidney slices. In the latter 

 issue, much more of the carboxyl group was converted to CO2, while the 

 acetoacetate formation was considerably less in kidney slices than in liver 

 slices. Moreover, the proportions of CO2 and acetoacetate obtained from 

 odd-carbon and even-carbon acids of varying chain length in kidney were 

 almost identical, in contrast to the marked variations in behavior exhibited 

 by these classes of fatty acids in liver slices. In the cyclophorase system 

 of Grafflin and Green '"^ derived from kidney and liver, the oxidation of the 

 C4 to C12 acids goes to completion. 



In an attempt to determine the extent of the extrahepatic oxi- 



««2 H. E. Himwich, W. Goldfarb, N. Rakeiton, L. H. Nahum, and D. DiiBois, Am. J. 

 Physiol, no, 352-356 (1934). 



««' D. R. ])rury and P. L). McMaster, J. Expll. Med., 49, 765-778 (1929). 



6«^ E. W. H. Ciuickt^hank and H. W. Kosterlitz, /. Physiol, 99, 208-223 (1941). 



^ M. B. Vi.«scher, Proc. Soc. Expll Biol. Med., 38, 323-325 (1938). 



««« S. Weinhouse, R. H. Millington, and M. E. Volk, /. Biol Chem., 185, 191-200 (1950). 



««' M. E. Volk, R. H. MilUngton, and S. Weinhouse, /. Biol Chem., 195, 493-501 

 (1952). 



^ R. P. Gejer and M. Cunningham, /. Biol Chem., 184, 641-646 (1950). 



683 R. P. Geyer, M. Cunningham, and J. Pendergast, J. Biol Chem., 185, 461-468 

 (1950). 



