CONVERSION OF FAT TO CARBOHYDRATE 225 



this foodstuff to sugar, then any increased consumption of fat should result 

 in an increased production of sugar. In the case of a diabetic animal, this 

 situation would be attended by an increased sugar secretion, with a re- 

 sultant rise in the D:N ratio. However, Lusk^^ reported that, when fat 

 metabolism was considerably increased in the fasting phlorhizinized dog, 

 either by shivering or by working the animals on a treadmill, no increase in 

 glycosuria occurred, provided that all residual glycogen had previously been 

 flushed out of the liver. In addition, it has been demonstrated in an equally 

 convincing manner, by other investigators,^^ -^^ that the normal D:N of 

 2.8 : 1 observed during fasting, when depancreatized dogs are used, is not 

 changed by subjecting the animals to cold or to work. On the basis of stud- 

 ies of the D : N ratio in fasting diabetic animals, in those which were fed fat, 

 or in those in which fat metabolism was markedly augmented by work or 

 by shivering, the weight of evidence is preponderant against the change of 

 fat to carbohydrate. 



(2) Respiratory Quotient 



The changes to be expected in the respiratory quotient (R.Q.) if fat were 

 converted to carbohydrate are the opposite of those which have been proved 

 for the carbohydrate -♦ fat transformation. In the former case, an oxygen- 

 poor substance (fat) would be converted to an oxygen-rich compound 

 (carbohydrate), with the result that a considerable quantity of oxygen must 

 necessarily be utilized from the respiratory gases. Under these conditions, 

 the observed R.Q. would be considerably below that for fat oxidation, i.e., 

 below 0.707. Pembrey,^^ in studies of the hibernating marmot, calculated 

 that the fat -* carbohydrate reaction, if allow^ed to take place exclusively in 

 the tissues, triolein being converted to glucose, would have a theoretical 

 R.Q. of 0.28, as calculated from the following equation: 



2C3H5(OCOCnH33)3 + 6402 > IGCeHizOe + I8CO2 + 8H2O 



Triolein Glucose 



Illustrating the Theoretical Conversion of Triolein to Glucose as Postulated by Pem- 



brey^' 



According to Lusk^ the following empirical equation represents the 

 change of palmitic acid to glucose. The theoretical R.Q. as pictured by 

 Lusk would be 0.69-0.70. 



«3 G. Lusk, Am. J. Physiol, 22, 163-173 (1908). 



" Y. Seo, Naunyn-Schmiedeberg's Arch, expil. Pathol. Pharmacol, 69, 341-363 (1908). 

 " W. H. Chambers, H. E. Himwich, and M. A. Kennard, /. Biol Chem., 108, 217- 

 225 (1935). 



" M. S. Pembrey, /. Physiol, 27, 66-84 (1901-1902). 



