TRIGLYCERIDES AND FATTY ACIDS 203 



will be the source of energy for work; they are largely utilized for the extra 

 calories produced for specific dynamic action, and they will serve to furnish 

 the means for the increased caloric expenditure occasioned by exposure 

 to low environmental temperatures. Likewise, the increased basal metabo- 

 lism resulting from an abnormal production of thyroxine, or from the ad- 

 ministration of thyroid, causes an increased fat oxidation if carbohydrate is 

 not available in a sufficient amount to supply the needed energy. Harel- 

 Ceddaha^-^ has shown that the oxidation of fatty acids required for the 

 chemical temperature regulation of warm-blooded animals submitted to 

 the action of cold is catalyzed by epinephrine. This hormone was found to 

 mcrease the oxidation of octanoic acid by liver homogenates. 



(8) The Inhibition of FatUj Acid Oxidation 



The oxidation of fatty acids can be inhibited by compounds which com- 

 pete for the enzymes with the normal oxidation products. Malonic acid, 

 HOOC • CH2 • COOH, is the best known of these inhibiting agents. Geyer, 

 Cunningham, and Pendergast^-^ reported that the effect of all inhibitors, 

 except maleic and malonic acids, on carboxyl-labeled octanoic acid, con- 

 sists in a decrease in both the CO2 and the acetoacetate formation by rat 

 liver slices. Although acetoacetate formation was inhibited to a greater ex- 

 tent than was CO2 formation, the ratio of labeling in the carbonyl and car- 

 boxyl groups in the acetoacetate remained normal. On the other hand, 

 malonic acid caused a decrease in the formation of CO2 from octanoate, but 

 an increase in radioactivity of both the carbonyl and the carboxyl groups of 

 acetoacetate. 



{9) The Oxidation and Metabolism of Par enter ally Administered Fats 



Although the administration of glucose and of amino acids by the in- 

 travenous route has been a routine procedure over a number of years, the 

 successful parenteral administration of fats has only recently been achieved. 

 The importance of developing a satisfactory procedure for the administra- 

 tion of fat by pathways other than the oral one has been recognized, since 

 the use of this foodstuff is necessary if caloric needs must be met by ex- 

 clusively intravenous feeding. The administration of fat intravenously has 

 the advantage of providmg not only a readily concentrated source of 

 calories but also one which possesses only slight osmotic properties. The 



'2* L. Harel-Ceddaha, Compt. rend., 236, 2114-2116 (1953). 



726 R. p. G(>ver, M. Cunningham, and J. Pendergast, J. Biol. Chem., 188, 185-191 

 (1951). 



