TRIGLYCERIDES AND FATTY ACIDS 199 



ized rabbits and dogs, as well as in diabetic dogs, rabbits, and a goat by- 

 Barnes et al.-^^ Friedemann^"*^ also reported that the rate of disappearance 

 of acetoacetate proceeded equally rapidly in normal, in phlorhizinized, and 

 in depancreatized dogs. Stadie and co-workers^^^ noted that, when shces of 

 liver and muscle were hicubated together, the ketones produced by the 

 liver were oxidized by the muscle. 



Although the presence of sugar does not appear to be necessary for the 

 oxidation of the ketone bodies in the isolated tissues, it is a well-known fact 

 that glucose spells the difference between the presence or the absence of 

 kctonuria in the fasting intact animal given ketogenic materials. Mirsky, 

 Nelson, and Grayman,"^ however, were unable to demonstrate any in- 

 creased rate of oxidation of injected /3-hydroxybutyrate in nephrectomized 

 rats if a proper correction was made for endogenous ketogenesis, irrespective 

 of whether or not glucose was given. On the other hand, Deuel et a/.,"^ in 

 tests patterned after those of Mirsky et al.,^''^ did note an increased rate of 

 disappearance of /3-hydroxybutyrate, in the case of rats, when glucose was 

 given. Additional evidence is necessary to answer this question more 

 fully. This relationship has been discussed more completely in an earlier 

 section (see page 172). 



The maximum proportion of the metabolism which can be assumed to be 

 due to the oxidation of ketone bodies is considerably under 100%. 

 Stadie^^*-^''^ calculated that, in the case of diabetic patients, the energy ob- 

 tained from the oxidation of the ketone bodies cannot account for more than 

 one-half to one-third of the total caloric needs from fat. Koehler, Windsor, 

 and HilP"^ reached the conclusion that acetoacetate does not have the 

 capacity to supply all the energy for sustenance in man. Their conclusions 

 were based upon the results of perfusion tests with acetoacetate in normal 

 subjects. Wick and Drury''^" arrived at essentially similar conclusions as 

 a result of experiments on rabbits. 



(7) Factors Affecting Fat Oxidation 



Although the hypothesis was formerly accepted by most biochemists that 

 fat is oxidized only when the carbohydrate reserves become depleted, this 

 concept cannot be accepted now, in view of the newer experimental results 

 obtained by the use of isotopes; the data indicate that fat is being de- 

 posited not only when the available carbohydrate is high, but also during 

 periods of fasting. The fat storage depots must be regarded as dynamic 



">8T. E. Friedemann, ./. Biol. Chem., 116, 1.33-161 (1936). 



™9A. E. Koehler, E. Windsor, and E. Hill, J. Biol. Chem., HO, 811-825 (1941). 



'" A. N. Wick and D. R. Drury, J. Biol. Chem., 138, 129-134 (1941). 



