420 



ADVENTURES IN RADIOISOTOPE RESEARCH 



follow that the half life-time of saturated fatty acids is less than one 

 day and that of unsaturated fatty acids about two days ; our data 

 indicate practically the same result, 0.8 and 2.2 days, respectively. 

 A closer coincidence is hardly to be expected in view of the fact that 

 even when comparing fatty acid turnover in the liver of rats of the 

 same race, age and weight, very appreciable fluctuations appear. Ame- 



iOO 



50- 



25- 





icorporation of ac'efate "Cinto saturorecl 

 faffy acids 



'>..^oss of "c by saturated fatty acids 



-V 



Fig. 1. Rate of incorpo- 

 ration of acetate C^* 

 (PiHL et al.) and rate of 

 loss of 1*0 by saturated 

 fatty acids extracted from 

 rat liver. ("Rise curve" 

 and "Decay curve".) 



4 days 



100 



ncorporation of acetate '^C into 

 unsarurated fatty acids 



Less of '*Cby unsaturated fatty acids 



4 days 



Fig. 2. Rate of incorpo- 

 ration of acetate "C 

 (PiHL et al.) and rate of 

 loss of "C by unsaturated 

 fatty acids extracted from 

 rat liver. 



lioration of purification or measuring methods would hardly lead to more 

 accurate mean renewal times, such could be obtained only by investi- 

 gating an appreciably larger number of animals. 



The significance of the data obtained is restricted, as both the satu- 

 rated and unsaturated fatty acids represent a mixture of components 

 having different turnover rates, some components of the unsaturated 

 fatty acid mixture as linoleic or linoleic acid are not synthesized in the 

 animal organism, and thus are not labelled. While Pihl and Bloch [8] 

 state that the linoleic acid content of the rat liver is almost negligable, 

 these authors find neutral fatty acids to contain 16 per cent, phospha- 

 tide fatty acids and 8 per cent of linoleic acid. From the fatty acids ex- 

 tracted from the liver of rabbits Popjak and Beeckmans [10] found 

 that when the acetate was given to the animals for 20 hr the specific 



