620 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



firmation of the hypothesis that the carbohydrate -*- fat change occurs in 

 adipose tissue. 



On the other hand, the R.Q. of adipose tissue obtained from fasting ani- 

 mals has been found in most cases to approach that of fat, namely, 0.71. 

 Mirski 122 reported a figure of 0.64, while a quotient of 0.78 was noted when 

 adipose tjssue was suspended in serum. In the case of the ground-squirrel, 

 Hook and Barron 476 found a respiratory quotient of 0.80 for the normal ani- 

 mal, and one of 0.67 in the adipose tissue of the hibernating animal, after 

 eight weeks of fasting. 



Most observers have reported fairly concordant results on oxygen con- 

 sumption. The following figures have been reported for Qo 2 (mm. 3 2 /hr./ 

 mg. fresh tissue) of adipose tissue 122 : from fasting rats, 0.12; from adipose 

 tissue containing glycogen, 0.18; from adipose tissue obtained from fasting 

 rats and suspended in serum, 0.18 and, with added glucose, 0.22; and in 

 other fat tissues containing glycogen, 0.38. The variation in R.Q. with 

 and without glycogen, as well as the increase in metabolic activity accom- 

 panying fat synthesis, are in accordance with the hypothesis that a synthe- 

 sis of fat from carbohydrate normally takes place in the adipose tissues. 430 



Although the experiments on rats with experimentally produced lesions 

 of the hypothalamus were not made on adipose tissue but on the whole ani- 

 mal, the data of Tepperman et al. 119 indirectly support the conclusion that 

 adipose tissue is one site for the carbohydrate -► fat change. Rats having 

 hypothalamic hyperphagia transformed carbohydrate to fat at a markedly 

 accelerated rate as compared with unoperated animals. However, it was 

 also found that, when normal rats consumed as much food as did the hyper- 

 phagic rats, within a short interval, correspondingly high R.Q. levels oc- 

 curred. The augmented rate of fat formation was therefore due to the 

 large accumulation of carbohydrate at one time, in the animal, rather than 

 directly to the hypothalamic injury. However, the speed of the carbohy- 

 drate -*• fat transformation was shown to be accelerated in the liver, as 

 shown by the R.Q. levels in in vitro tests obtained on slices prepared from 

 livers of normal rats trained to consume their food within a short interval. 477 



(6) Enzyme Activity in Adipose Tissue 



There is some disagreement as to whether the enzymatic activity noted in 

 extracts of adipose tissue arises from enzymes elaborated by this tissue or 

 whether it represents activity on the part of enzymes carried there by the 



« 8 W. E. Hook and E. S. G. Barron, Am. J. Physiol., 133, 56-63, 334 P (1941). 

 « 7 V. C. Dickerson, J. Tepperman, and C. N. H. Long, Yale J. Biol. Med., 15, 875-892 

 (1943). 



