158 III. OXIDATION AND METABOLISM 



find any relationship between the level of ketoniiria and the liver fat 

 content per se, or between the amount of lipotropic agents such as methio- 

 nine or choline, or of a liver-fattening substance, for instance cystine, and 

 the degree of fasting ketonuria in the rat. On the other hand, it is suggested 

 that the rapidity of onset and the degree of ketosis are inversely related 

 to the protein content of the preceding diet. The hypothesis is advanced 

 that this effect is related to the amount of protein stored prior to the onset 

 of the fasting period. The greater the amount of stored protein available 

 in the tissues at the onset of the starvation regimen, the larger the potential 

 reserve of antiketogenic material for catabolism during fasting. Such 

 antiketogenic material assists the rats in maintaining their liver glycogen 

 and blood sugar at higher levels. Tidwell and Treadwell"*^** also reported 

 that the preceding protein intake by rats is a major dietary factor affecting 

 the degree of the subsequent fasting ketonemia. In a later communication, 

 these workers'*''^ stated that the reduction in ketonuria was not due to a 

 metabolic lag or to an increased flushing out of metabolic end-products 

 during the fast. Rather, it appeared to be related to the increased protein 

 catabolism which occurred during the period of the fast. However, the 

 administration of an amount of glucose equivalent to that formed by the 

 increased rate of protein catabolism failed to produce the corresponding 

 antiketogenic effect previously attributed to it. It is suggested that the 

 greater fasting ketosis noted following a low-protein diet may be related 

 to an increased rate of utilization of carbohydrate by these animals, as 

 indicated by the rapid disappearance of liver glycogen. Apparently, 

 more experimental work is needed before the relationship between fatty 

 livers and fasting ketonuria is clarified. 



(e) Adaptation as a Factor in Ketonuria. It has been generally con- 

 sidered by some nutritionists that adaptation to ketonuria may occur. 

 Thus, Heinbecker^^^"^''* reported that three successive groups of fasting 

 Eskimos developed a lower degree of ketonuria than is usual in the case of 

 white persons living in the temperate zones. He suggests that the mecha- 

 nism for the oxidation of fat is modified, since the Eskimo is able to burn 

 a considerable amount of fat to completion without the aid of carbohydrate. 

 The levels of plasma lipids of Arctic Eskimos^'^^ are similar to those con- 

 sidered normal for white individuals in the temperate zones. The question 



«oH. C. Tidwell and C. R. Treadwell, /. Biol. Chem., 162, 155-161 (1946). 



«i H. C. Tidwell and C. R. Treadwell, /. Biol. Chem., 164, 313-319 (1946). 



«2P. Heinbecker, /. Biol. Chem., 80, 461-475 (1928). 



"73 P. Heinbecker, /. Biol. Chem., 93, 327-336 (1931). 



«" P. Heinbecker, /. Biol. Chem., 99, 279-282 (1932-1933). 



«5 A. C. Corcoran and I. M. Rabinowitch, Biochem. J., 31, 343-348 (1937). 



