720 VII. LIPID DISTRIBUTION IN SPECIFIC TISSUES 



fats. Thus, the suggestion of Ohlsson and Blix 105 that the lipids in the 

 liver undergo a cyclic variation is not surprising. These workers report 

 that the neutral fat of rat liver varies with the time of day, accumulating 

 during the early hours of the day and decreasing during the afternoon. It 

 has been stated that this variation occurs independently of food intake. 

 Moreover, the high-fat phase of the liver coincides with the low-glycogen 

 phase of this organ, and vice versa. It is possible that a physiologic con- 

 trol is exerted which causes fat to pass into the liver when the glycogen store 

 becomes depleted. 



Forsgren, 106 on the basis of histochemical evidence, first described a diur- 

 nal variation in liver glycogen in the rabbit. This observer was convinced 

 that an assimilatory cycle occurs during the night when the glycogen 

 storage is at its maximum and bile production is at its minimum. These 

 results were confirmed by Agren et al. 107 on rabbits, rats, and mice by the 

 demonstration that increased resistance to insulin occurs concomitantly 

 with the period of increased glycogen retention. Moreover, an increased 

 excretion of urinary nitrogen was noted in fasted as well as in non-fasted 

 rabbits during the night, as contrasted with the values during the day. 

 On the other hand, Higgins, Berkson, and Flock 108 challenged the hypothesis 

 that such diurnal variations are independent of nutritional differences. 

 They reported that, although diurnal variations were noted in rats fed at 

 9 to 11 A.M., this phenomenon was not repeated on the following day if the 

 animals were fasted. Moreover, the liver glycogen was practically constant 

 in various groups of rats, six hours after feeding periods spaced at two-hour 

 intervals during the day and night. 109 These results were confirmed by 

 Deuel and collaborators, 110 who concluded that the cyclic variations were 

 solely of dietary origin. 



Thus, although it is possible that the diurnal variation in the neutral fat 

 content of the liver may be independent of ingested fat, it may be related 

 to the liver glycogen level. Under such conditions, it would be linked only 

 secondarily to the nutritional status as reflected in the cyclic content of 

 liver glycogen. 



e. The Effect of Hormones on Liver Lipids. A number of hormones 

 are of importance in controlling fat distribution and utilization, in addi- 



105 B. Ohlsson and G. Blix, Skand. Arch. Physiol, 69, 182-188 (1934). 



106 E. Forsgren, Skand. Arch. Physiol, 53, 137-151 (1928). 



107 G. Agren, O. Wilander, and E. Jorpes, Biochem. J., 25, 777-785 (1931). 



108 G. M. Higgins, J. Berkson, and E. Flock, Am. J. Physiol., 102, 673-682 (1932). 



109 G. M. Higgins, J. Berkson, and E. Flock, Am. J. Physiol, 105, 177-186 (1933). 



110 H. J. Deuel, Jr., J. S. Butts, L. F. Hallman, S. Murray, and H. Blunden, J. Biol 

 Chem., 123, 257-265 (1938). 



