PHYSIOLOGY OF ADIPOSE TISSUE 607 



On the other hand, the unsaturation of the triglyceride fatty acids changed 

 in the opposite direction, being highest in the mitochondria and lowest in 

 the homogenic phase. 



The distribution of cholesterol as the ester and free alcohol was investi- 

 gated by Alfin-Slater and co-workers, 396 by Rice et al., m and by Schotz, 398 

 who used a modification of the Schneider-Hogeboom centrifugation tech- 

 nic. 399 It was found that the esterified cholesterol was largely present in 

 the "cream" layer, which represents unorganized material from the cyto- 

 plasm, while the free cholesterol was concentrated in the microsomal frac- 

 tions. Using a similar technic, Krinsky and Ganguly 400 demonstrated that 

 vitamin A occurs in different fractions of the liver, depending upon whether 

 it is in the form of the free alcohol or of the ester. The vitamin A ester 

 was found in the fat of the cream layer, whereas the alcohol occurred in the 

 particulate matter as well as in the cream. 



7. The Physiology of Adipose Tissue 



Adipose tissue has long been considered to be an accumulation of inert 

 fatty material which possesses little or no metabolic activity. However, 

 this viewpoint has been challenged by Wertheimer and Shapiro, 4 H in a re- 

 view on adipose tissue. These workers maintain that fatty tissue consti- 

 tutes an important link in the metabolic processes of the animal. Wells 402 

 likewise reviewed this topic from the anatomical and pathological view- 

 point, and arrived at essentially the same conclusion. In this section, 

 evidence will be summarized which indicates that adipose tissue has an 

 independent origin, reacts to stimuli other than those activating the ad- 

 joining connective tissues, has its specific blood supply, and responds in its 

 own characteristic way to factors which alter its metabolism. 



(1) The Specific Nature of Adipose Tissue 



The view is still quite widespread that adipose tissue is nothing more 

 than connective tissue in which the fatty cells have been laid down. How- 

 ever, adipose tissue has been shown to develop from specific primitive 



396 R. B. Alfin-Slater, L. I. Rice, and M. C. Schotz, Federation Proc., 12, 167 (1953). 



397 L. I. Rice, M. C. Schotz, R. B. Alfin-Slater, and H. J. Deuel, Jr., J. Biol Chem., 201, 

 867-871 (1953). 



398 M. C. Schotz, L. I. Rice, and R. B. Alfin-Slater, /. Biol. Chem., 204, 19-26 (1953). 



399 W. C. Schneider and G. H. Hogeboom, J. Biol. Chem., 188, 123-128 (1950). 



400 N. I. Krinsky and J. Ganguly, J. Biol. Chem., 202, 227-232 (1953). 



401 E. Wertheimer and B. Shapiro, Physiol. Revs, 28, 451-464 (1948). 



402 H. G. Wells, /. Am. Med. Assoc., 114, 2177-2183, 2284-2289 (1940). 



