638 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



nounced than is that of the male rats. Even after the choline-free diet had 

 been fed for only twenty-four hours, the liver lipids were increased from 

 3.15 to 7.54% in the female rats. Moreover, the values for liver lipid re- 

 mained consistently higher in the female rats, and the water content of the 

 liver was uniformly lower than in the male rats. 



The disappearance of the lipid from the liver occurred at a much slower 

 rate than did its accumulation. Thus, after five days of fasting, in the 

 case of rats which had fatty livers, a further increase of fat was observed in 

 all experiments with male rats. 564 The increases were as follows for the 

 several groups : days (controls), 1.49; 1 day, 3.25; 3 days, 4.75; 6 days, 

 3.43; 9 days, 2.83; 12 days, 0.53; and 16 days, 2.59%. However, in the 

 case of female rats, the increases in liver lipids during the fasting period were 

 invariably less than in the male animals. This reflects the higher metab- 

 olism of fats in the female. The changes in the several groups of female 

 rats after a five-day fasting period were as follows : days (control) , + 1.59 ; 

 1 day, -1.82; 3 days, +2.11; 6 days, -2.65; 9 days, +2.31; 12 days, 

 +0.49; and 16 days, -5.76%. 



On the other hand, when male rats having fatty livers were given the 

 stock diet without fasting, the liver fat decreased rapidly, but was still 

 slightly elevated after twenty-one days. When betaine hydrochloride, 

 which possesses a lipotropic action, was also administered, the decrease in 

 liver lipids was much more precipitous. However, even in this case, the 

 lipid metabolism remained quite susceptible to inanition, since the response 

 to fasting as indicated by increased liver lipids was greater than in the case 

 of normal rats. Finally, another index of fat metabolism, namely fasting 

 ketonuria, has been shown to remain elevated for seven days after rats with 

 fatty livers were placed on the stock diet, although the response was re- 

 duced more rapidly in rats receiving betaine hydrochloride. These results 

 are summarized in Table 22 (page 637). 



The source of the lipid in fatty livers is also of interest. Li and Free- 

 man 565 demonstrated that the fat accumulating in the liver of a protein- 

 deficient dog is largely exogenous in origin. This was indicated by the 

 fact that the fat content of the livers was higher on the high-fat, protein- 

 deficient diet, with or without cholesterol, when bile salts were added. 

 This hypothesis is also supported by the fact that the fat content of the 

 liver increased when the dietary fat was augmented. Channon et oZ. 566 

 have concluded, on the basis of experiments on rats, that the extent of fatty 



565 T. W. Li and S. Freeman, Am. J. Physiol, 145, 667-675 (1946). 



566 H. J. Channon, S. W. F. Hanson, and P. A. Loizides, Biochem. J., 36, 214-220 

 (1942). 



