596 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



circumstances, if one molecule of the fat were used at a time, a greater pro- 

 portion of these shorter-chain acids would be utilized, while only one-half 

 the amount of the Cis acids was being oxidized. The data of Longenecker 

 are summarized in Table 18. 



Table 18 



The Effect of Fasting on the Content of Principal Fatty Acids of Rats 



Previously Fed a Coconut Oil Diet" 



Fasted groups 



15% loss in 30% loss in 



body weight body weight 



Non-fasted 



Acids group, g. Grams % utilized Grams % utilized 



Total acids 13.50 8.46 37.3 4.95 63.7 



Laurie (C 12 ) 3.60 1.69 53.1 0.92 74.4 



Myristic (C M ) 2.34 1.56 33.3 0.70 69.9 



Palmitic (C 16 ) 2.69 1.73 35.8 0.80 70.1 



Oleic (C 18 ) 3.21 2.63 19.1 1.73 46.2 



« H. E. Longenecker, /. Biol. Chem., ISO, 167-177 (1939). 



Black and her co-workers 341 recorded an interesting phenomenon related 

 to the caloric intake in the Cape John dory {Zeus cayensis C. and V.). The 

 composition of the fat differed, depending upon whether it was obtained 

 from the thin or from the fat fish. Whenever an increased fat content was 

 present in the fish, the proportion of highly unsaturated C20, C22, and C24 

 acids was increased, not only in the body fat but also in that in the liver. 



h. The Effect of Thyroxine on the Distribution of Storage Fat. When 

 thyroxine was administered to rats, there was a marked reduction in the 

 total fat laid down. 288 This result is not unexpected, in view of the fact 

 that the thyroid hormone may increase heat production to such an extent 

 that it is no longer possible for the animal to have a sufficient surplus of 

 calories to provide for the deposition of fat. One interesting feature 

 brought out by the experiments of Reed et al. m is the finding that, despite 

 the fact that the total fat laid down was decreased more than 50% when 

 thyroxine was fed, no change in distribution could be observed. Appar- 

 ently all fat depots were equally affected. In contradistinction to the re- 

 sults on ovariectomized rats, the degree of saturation of the fat of the thy- 

 roxine-fed rats was found to be changed. Whereas the average iodine num- 

 ber of the body fat stored in the several fat depots was 33.3 in the normal 

 rats, it amounted to 41.2 and 45.2 in the rats fed the identical diet but 



341 M. M. Black, W. S. Rapson, H. M. Schwartz, and N. J. Van Rensburg, J. Soc. 

 Chem. Ind., 65, 13-15 (1946). 



