540 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



ported by Pembrey 111 for the hibernating marmot; Grafe 112 observed a non- 

 protein R.Q. (total R.Q. corrected for that due to the protein moiety) of 

 1.31 for dogs given 300% of their daily requirement as carbohydrate. 

 Finally, Wierzuchowski and Ling, 113 working in Lusk's laboratory, ob- 

 tained an average non-protein R.Q. of 1.40 in a pig, for a period of twenty 

 hours after the ingestion of 700 g. of starch ; the maximum value noted for a 

 single period was 1.58. It was calculated that fat was synthesized at a 

 maximum rate of 7.1 g. per hour. During the twenty-four hour period, a 

 total of 125 g. of fat was produced, with an average hourly production of 

 5.2 g. Under these unusual conditions, 27% of the metabolized starch was 

 required to satisfy the basal metabolism, and 13% was expended for the 

 specific dynamic action. The balance of 56% of the polysaccharide was 

 estimated to be converted to fat. 



Although it was formerly considered by some investigators that the 

 conversion of carbohydrate to fat occurs only when the R.Q. exceeds 1.00, 

 this concept is not held at the present time. It is certain that the 

 formation of fat continues to take place even when the R.Q. is consider- 

 ably below 1.00. Although the level of the R.Q. is without question an 

 index of the intensity of the carbohydrate — » fat reaction, this transforma- 

 tion will still proceed, at a slower rate, when the oxidation of carbohydrate 

 and protein becomes the predominant reaction and thus results in a masking 

 of the higher respiratory quotient. This dynamic concept of fat synthesis 

 is in line with the results of Schoenheimer and Rittenberg, 41 which demon- 

 strate that a constant and rapid exchange of fat occurs in the fat depots. 

 Moreover, the adipose tissues offer a site for the temporary storage of the 

 caloric reserves after heavy carbohydrate meals, when the capacity of the 

 storage facilities for glycogen may be inadequate to store the unoxidized 

 reserves as glycogen. In fact, making use of injected deuterium oxide, 

 Stetten and Boxer 114 demonstrated that the major part of administered 

 glucose which is not burned is converted directly to fat by the rat, and does 

 not undergo a preliminary transformation to glycogen. On the other 

 hand, in the fasted rat, which possesses considerable additional storage 

 capacity for glycogen over that afforded in the well-fed animal, a much 

 larger proportion of administered glucose is converted to glycogen. 115 



b. The Site of Conversion of Carbohydrate to Fat. Although one is 

 naturally led to ascribe to the liver the function of mediating the carbo- 



111 M. S. Pembrey, J. Physiol, 27, 407-417 (1901-1902). 



112 E. Grafe, Devi. Arch. klin. Med., 113, 1-91 (1914). 



113 M. Wierzuchowski and S. M. Ling, J. Biol. Chem., 64, 697-707 (1925). 



114 De W. Stetten, Jr., and G. E. Boxer, J. Biol. Chem., 155, 231-236 (1944). 

 116 G. E. Boxer and De W. Stetten, Jr., J. Biol. Chem., 155, 237-242 (1944). 



