SATURATED FATTY ACIDS 39 



the administration of a carbohydrate-free diet composed entirely of pro- 

 tein or of protein and fat resulted in a marked depression in hepatic hpo- 

 genesis. The ingestion, for three days, of a diet in which carbohydrate 

 was the sole source of calories did not influence hepatic lipogenesis, al- 

 though this function was somewhat reduced m animals maintained on an 

 exclusively carbohydrate regimen for ten days. In this case, the decrease 

 in fat synthesis might be related to an insulin deficiency, inasmuch as the 

 insulin content of the pancreas is believed to be due in large part to the 

 amount of available carbohydrate in the diet.^^^-"^ A variation in the 

 effect of insulin in producing lipogenesis in the livers from fasted and from 

 fed rats has already been reported. Haugaard and Stadie^'''* were likewise 

 able to correlate the glycogen content of the liver of rats with their ability 

 to synthesize fatty acids from acetate. 



c. X-Irradiation. Whole body x-irradiation has been shown to have a 

 profound effect on the rate of conversion of acetate-1-C^^ to fatty acid C^^ 

 by liver slices. The inhibition of the conversion of acetate to fatty acids in 

 fasting rats was shown by Lerner et al}''^ to be removed by exposing the 

 rat to whole body irradiation. Liver sUces obtained forty-eight to seventy- 

 two hours after x-irradiation with 2500 r, formed more than twice as much 

 fatty acid as did sUces from fed rats, and ten times as much as slices from 

 fasted control rats. In the case of previously fasted rats, x-irradiation 

 was shown to raise the rate of lipogenesis to two-thirds of that of the 

 normally fed rat. 



Altman et al.^''^ reported a somewhat similar effect exerted by x-irradi- 

 ation on bone marrow. In this case, the rate of synthesis of fat from ace- 

 tate by bone marrow homogenates was doubled shortly after x-irradi- 

 ation. However, it had returned to a normal value within forty-eight 

 hours, after which it dropped to 58% below preirradiation values at the 

 end of 158 hours. The synthesis of unsaturated fatty acids was the factor 

 primarily affected by x-irradiation. 



d. Species. The variation in the insulin effect on lipogenesis as re- 

 lated to species, which has already been discussed, is only one phase of this 

 problem. Thus, Balmain et al.^'''' reported that rat liver slices incorporated 

 about eight times as much glucose carbon and one-sixth as much acetate 

 carbon in fatty acids as did liver slices from sheep. Whereas sheep shces 



i"3 R. E. Haist, Physiol. Revs., 24, 409-444 (1944). 



''*E. S. Haugaard and W. C. Stadie, J. Biol. Chem., 199, 741-744 (1952). 

 "^ S. R. Lerner, W. L. Warner, and C. Entenman, Federation Proc, 12, 85 (1953). 

 ''^ K. I. Altman, J. E. Richmond, and K. Salomon, Biochem. et Biophi/s. Acta, 7, 

 460-465 (1951). 



^" J. H. Balmain, S. J. Folley, and R. F. Glascock, Biochem. J., 53, xxvi-xxvii (1953). 



