TRANSFORMATION OF CxLYCEROL TO GLUCOSE 213 



fed in aqueous solution, and this retards the appearance of glycogen in the 

 liver. Finally, it is possible that a large part of the glycerol administered in 

 neutral fat is not set free from the fatty acids if the Frazer concept is cor- 

 rect that fat is absorbed largely as triglycerides, together with smaller pro- 

 portions of diglycerides or monoglycerides. Even if glycerol were com- 

 pletely liberated in the gut, one would expect it, or a comparable amount of 

 newly-synthesized glj^cerol originating from carbohydrate, to be used in the 

 synthesis of neutral fat from the free fatty acids which would be absorbed. 

 In neither of these situations would glycerol be available to be converted to 

 glucose or, at least, to result in the net synthesis of glucose. 



On the other hand, when the triglycerides which are fed cannot be stored 

 in the tissues, the combined glycerol can be utilized as a source of glucose or 

 glycogen. Thus, when neutral fats such as triacetin, tributyrin, tricaproin, 

 or tricaprylin are fed, glycogenesis can be demonstrated. ^'-^^ These fats 

 cannot be deposited as such in the fat depots of the rat.-^-^* However, the 

 feeding of trilaurin results in a deposition of as much as 25% of lauric acid 

 in the depot fat.-^ The rapid digestion and absorption of triacetin and tri- 

 butyrin,-^ which exceeds that of all natural fats which have been investi- 

 gated, would make the glycerol available for glycogenesis within a rela- 

 tively short period, and so accentuate the extent of glycogen formation. 

 It seems probable that the small amount of liver glycogen which has been 

 reported in the livers of rats previously fasted for twenty-four hours, and 

 then fed butterfat for three to eight days,"'^^ may be traced to the glycerol 

 available from tributyrin. 



Glycogen can also originate from the glycerol moiety of the triglycerides 

 of the short-chain fatty acids having an odd number of carbon atoms; 

 these triglycerides, likewise, cannot be stored in the fat depots. However, in 

 this case, the fatty acids as well as the glycerol serve as the source of carbo- 

 hydrate. Thus, when tripropionin is fed to rats, the extent of the glyco- 

 gen deposition considerably exceeds that obtained after triacetin or tri- 

 butyrin. 2- 



(3) Quantitative Studies 



It has been generally agreed that glycerol is quantitatively converted to 

 glucose in the animal body. Although Cremer,-^ using phlorhizinized dogs 



" H. C. Eckstein, /. Biol. Chem., 81, 613-628 (1929). 



2* H. C. Eckstein, /. Biol. Chem., 84, 353-357 (1929). 



2* M. Powell, J. Biol. Chem., 89, 547-552 (1930). 



«« H. J. Deuel, Jr., and L. Hallman, J. Nutrition, 20, 227-232 (1940). 



" D. E. Gregg, /. Nutrition, 4, 385-398 (1931). 



« C. L. Gemmill and E. G. Holmes, Biochem. J., 29, 338-349 (1935). 



" M. Cremer, Munch, med. Wochschr., 49, 944 (1902). 



