CONVERSION OF FAT TO CARBOHYDRATE 231 



sary to take into consideration not only glycogen hut free sugar, lactic acid, 

 urea, glycerol, and fatty acids, both in the liver and also in the perfusing 

 fluid. Although Stewart and Thompson ^^^ noted an increase in carbohy- 

 drate in liver slices, along with a decrease in fatty acids, the oxygen consump- 

 tion was too low to justify the conclusion that a transformation of fatty acid 

 to carbohydrate had occurred. 



Although not all these criticisms are valid for all the perfusion experi- 

 ments which purport to show the transformation of fat to carbohydrate, 

 they have not all been completely refuted. Thus, Richardson* suggests that 

 lactic acid formed in the tissues because of the anaerobic conditions which 

 existed therein prior to the start of the perfusion might well be responsible 

 for a considerable proportion of the new glucose formed when perfusion 

 with oxygenated solution was begun. On the other hand, Page and Young^^ 

 believed that sufficient glycerol was available to account for the sugar for- 

 mation in the experiments of Jost.'-^ Lastly, Gregg^^^ is of the opinion that 

 some of the new sugar reported in the case of cats and dogs may have 

 originated from liver glycogen, which had been assumed to be zero but which 

 was probabl}'- still present to an appreciable although small extent. More- 

 over, since the glycogen content of different lobes of the liver varies, one 

 cannot accept the value of any one lobe as representative of the entire 

 liver. 



b. Fat Change and Respiratory Quotient. The variations of R.Q. in 

 tissues such as the liver have been interpreted as offering support for the 

 fat -> carbohydrate transformation. Thus, the R.Q. of liver slices from 

 animals w'hich had been well fed ranged between 0.85 and 0.75. When this 

 organ had been excised from rats whose carbohydrate stores were depleted, 

 either by fasting or by a high-fat diet, values for the R.Q. below^ 0.70 were 

 recorded by Meyerhof and Lohmann,^^° and by Soskin and Mirsky.^^^ 

 Dickens and Simer^^- reported R.Q. levels below 0.70 only when the tests 

 were carried out with phosphate- or bicarbonate-buffered Ringer's solution. 

 Gemmill and Holmes-^ observed a low R.Q. in liver slices obtained from rats 

 previously on a high-fat regimen. Some increase in fermentable carbohy- 

 drate also occurred in the liver during the course of the test. However, Cori 

 and Shine '^^ also found an increase in fermentable carbohydrate when 

 glycerol or /^-glycerophosphate was added. Moreover, Stadie and co- 



129 C. P. Stewart and J. C. Thompson, Biochem. J., 35, 245-253 (1941). 

 "o O. Meyerhof and K. Lohmann, Biochem. Z., 171, 381-402 (1926). 

 »" S. Soskin and I. A. Mirsky, Am. J. Physiol., 114, 106-109 (1935). 

 1" F. Dickens and F. Simer, Biochem. J., 25, 985-993 (1931). 

 1" C. F. Cori and W. M. Shine, Science, 82, 134-135 (1935). 



