586 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



tyric acid, or other ketogenic acids are given as their sodium salts to fasting 

 rats and guinea pigs. 291 Beach and co-workers 292 recently confirmed this 

 sex difference in ketonuria occurring in alloxan diabetes. Moreover, the 

 high ketonuria noted in the normal female rat was reduced following ovari- 

 ectomy to the value found in the normal male animals. 293 Finally, a similar 

 sex difference was also noted in the endogenous ketonuria occurring in rats 

 with fatty livers produced by fasting without the administration of supple- 

 mentary ketogenic acids. 277 Although these data do not prove that a sex 

 difference obtains in the lipid composition of rats, they do indicate that a 

 quantitative variation must exist in the intermediary metabolism of lipids 

 as related to sex. 



Finally, the relationship of the higher lipid values in the liver to the in- 

 creased level of fat metabolism in the female as contrasted with the male 

 animal is evident from later studies by the Deuel group. 294 After the pro- 

 duction of fatty livers in male and female rats by the administration of a 

 choline-free, high-fat diet, a greater decline in the value of liver lipid ob- 

 tained in the females than in the males during a subsequent fasting period. 

 This increased rate of decrease in liver lipid in the female occurs coinci- 

 dentally with the higher level of endogenous ketonuria produced during this 

 period, as compared with that in the males. 



d. The Effect of Environmental Temperature, (a) The Effect on Ani- 

 mal Fats. There is some evidence that environment may also play a role in 

 determining the type of fat laid down in the animal. Thus, the fat of fishes 

 living in cold water and that of aquatic animals which inhabit the Arctic 

 regions have a much lower melting point than do those from animals from 

 tropical regions. Lovern 295 has shown that the fat from the tuna or tunny 

 (Thunnus ihynnns), which spends a considerable portion of time in rela- 

 tively warm water, and which likewise has a body temperature 3°C. higher 

 than the water, differs from that of other marine fats in several respects. 

 This fat contains less myristic acid, more palmitic acid, and an unusual pro- 

 portion of stearic acid. In the unsaturated acids, the average unsaturation 

 is less than that in other marine animals. All of these differences in com- 

 position tend to produce a fat having a higher melting point. 



291 J. S. Butts and H. J. Deuel, Jr., J. Biol. Chem., 100, 415-428 (1933). 



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

 (1951). 



293 C. F. Grunewald, C. H. Cutler, and H. J. Deuel, Jr., /. Biol. Chem., 105, 35-43 

 (1934). 



294 H. J. Deuel, Jr., S. Murray, L. F. Hallman, and D. B. Tyler, /. Biol. Chem., 120, 

 277-288 (1937). 



296 J. A. Lovern, Biochem. J., 20, 2023-2026 (1936). 



