612 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



site for the synthesis of fat from carbohydrate. The fact that adipose 

 tissue containing glycogen has an R.Q. greater than unity 122 ' 429 offers sup- 

 port for such an hypothesis. These observations are supported by the re- 

 sults of Henle and Szpingier, 121 who demonstrated that, in the isolated adi- 

 pose tissue of the rat, the R.Q. rose above unity simultaneously with the 

 disappearance of glycogen. Finally, the data of Shapiro and Werthei- 

 mer, 430 which indicated the incorporation of stably bound deuterium into the 

 fatty acids of adipose tissue incubated in vitro in serum with D 2 0, would 

 seem to be excellent proof of the above assumption. 



c. The Control of Fat Mobilization and Deposition, (a) The Metab- 

 olism of Adipose Tissue as a Controlling Factor. The factors which control 

 the deposition or withdrawal of fat from the adipose tissue are not clearly 

 understood. Apparently the level of fat in the blood is not a deciding fac- 

 tor since, in conditions of fat depletion, as for example in fasting phlorhi- 

 zinized rats, a marked hyperlipemia obtains concomitantly with a mobiliza- 

 tion of the fat from the depots. 



On the other hand, Shapiro and his collaborators 431 reported that the 

 balance between deposition and mobilization is controlled by a factor acting 

 directly within the fat cell. Thus, it was shown by in vitro tests that the 

 fat-depleted tissue, but not the fat-laden cells, can readily take up fat from 

 serum at 38°C; however, this uptake of fat can readily be prevented by 

 heating the tissue to 80°C, by the addition of sodium cyanide and sodium 

 fluoride, or by lowering of the temperature to 20°C. Moreover, azide did 

 not prevent the transfer of fat from the incubation medium to the cells. 

 The penetration of fats into the cells is therefore an active process depend- 

 ing upon the metabolism of the cells. It would seem logical to suppose 

 that the rate of exchange could also be subject to hormone control, as well 

 as to nervous regulation. These possibilities are discussed below. 



(b) Hormone Control of Fat Mobilization and Deposition in Adipose Tissue. 

 The endocrine control of fat deposition and mobilization has been demon- 

 strated in the case of the anterior pituitary hormone, the adrenocortical 

 hormones, insulin, and the thyroid hormone. These are discussed in turn 

 below. 



a'. The Regulation by the Anterior Pituitary Gland: Barrett, Best, 

 and Ridout, 432 and Stetten and Salcedo, 433 using deuterio-labeled fats, dem- 



429 T. Ruska and T. Oestreicher, Arch, expll. Pathol. Pharmakol. (Naunyn-Schmiede- 

 berg's), 177, 42-52 (1934). 



430 B. Shapiro and E. Wertheimer, J. Biol. Chem., 173, 725-728 (1948). 



431 B. Shapiro, D. Weissmann, V. Bentor, and E. Wertheimer, Nature, 161, 482 (1948). 



432 H. M. Barrett, C. H. Best, and J. H. Ridout, J. Physiol, 93, 367-381 (1938). 



433 De W. Stetten, Jr., and J. Salcedo, Jr., /. Biol. Chem., 156, 27-32 (1944). 



