TRIGLYCERIDES AND FATTY ACIDS 155 



to 4% in males (and to lower values in females). These new levels are 

 maintained until the rats are seventeen to twenty-four months of age. 

 Since the level of ketonuria is usually inversely related to the carbohydrate 

 stores, one would expect a lower susceptibility to ketonuria in very young 

 rats. 



(c) Sex as a Factor in Ketonuria. The most important physiologic factor 

 which influences the level of ketonemia and ketonuria is undoubtedly sex. 

 There is ample evidence that the pattern of fat metabolism is quite different 

 for the female than it is for the male. Thus, it was noted earlier that the 

 storage fats m the female are greater in amount than in the male. More- 

 over, the situation is reversed in the case of glycogen, which appears to be 

 stored at a higher level in the male rat as contrasted with the female (see 

 The Lipids, Vol. II, Chapter VI). 



The principal organ in which sex differences in fat storage can be observed 

 is the 'liver. In most cases of unfasted animals, and in practically all 

 instances m which fasted rats are tested, it can be shown that liver glycogen 

 values are higher in the male, and liver lipids higher in the female, than in 

 the livers of the opposite sex. However, the higher level of liver lipids in 

 the female rats, as contrasted with the male animals, is confined to the 

 neutral fat, as the average cholesterol and lecithin appear to be higher in 

 the livers of males than in this organ in the females. 



The sex difference in fat metabolism is exhibited most strikingly in rela- 

 tion to ketosis. In the previous section on the effect of species on keto- 

 nemia and ketonuria, it was pointed out that spontaneous ketonemia in 

 cattle, sheep, goats, and hogs occurs only in the female. Sampson^^^ 

 states that so far as he is aware "evidence has not been presented to show 

 that significant ketonemia occurs in steers, bulls, wethers, and rams, no 

 matter what the disease with which they are affected." He states further: 

 "A significant spontaneous ketosis of the ovine and bovine species in this 

 country is limited almost exclusively to females during pregnancy and 

 lactation . . . ." 



In the case of rats, although there is no sex difference in the shght 

 ketonuria occurring during fasting, the female excretes a much larger pro- 

 portion of ketone bodies after the feeding of ketogenic acids than does the 

 male, in the condition described as exogenous ketonuria. ^^*''*^ The same 

 situation obtains in rats with fatty hvers (endogenous ketonuria), in the 

 spontaneous ketonuria which results on fasting. ^^"^ Beach and associates*^' 

 noted that a similar sex difference obtains in the ketonuria occurring after 



^" E. F. Beach, P. J. Bradshaw, and N. R. Blatherwick, Am. J. Physiol, 166, 364-373 

 (1951). 



