822 



ADVENTURES IN EADIOISOTOPE EE SEARCH 



Carbon-14 of the acetate administered can be incorporated into other 

 carbon compounds either after oxidation to carbon dioxide or directly 

 without oxidation. For example, acetate may contribute carbon atoms 

 to the glucose units of glycogen by pathways other than those of oxidation 

 and carbon dioxide fixation^^\ In both cases, increased catabolism as such 

 produced ))y muscular exercise can be expected to lead to a diminished 

 incorporation of carbon-14 into many of the tissue constituents. Follow- 

 ing the injection of labelled acetate, apart from a brief initial period, as 

 shown by Gould and associates^^^ the specific activity of the carbon 

 dioxide decreases very markedly with time. This decrease is interpreted 

 as being primarily clue to a dilution of radioactive carbon dioxide of 

 the body fluid with normal carbon dioxide resulting from other metabolic 

 processes. An increased metabolism can thus be expected to lead to an 

 increased rate of dilution and to a correspondingly enhanced rate in 

 the decrease of the specific activity of the labelled carbon dioxide with 

 time, leading in turn to a decrease in the amount of carbon-14 incor- 

 porated into the tissue constituents. 



Effect of (a) Muscular Exercise and (b) Urethane Administration on the 

 Incorporation of Carbon-14 into Tissue Constituents of Mice. Each Mouse 



Injected, 26,600 Counts 



(a) 



(t>) 



20 min (19.0 gm mouse) 270 min (21.2 gm mouse) 



Fractiou 



Counts per min 



Plasma total 



Liver total 



Liver fatty products* 



Liver glycogen 



Kidney total 



Kidney fatty products 



Kidney protein 



Intestinal mucosa total 

 Intestinal mucosa fatty 



products 



Intestinal mucosa 



protein 



Muscle total 



Muscle fat 



Muscle protein 



Brain total 



Brain fat 



Brain protein 



Control 



97.0 

 156.5 

 50.5 

 20.4 

 55.5 

 14.3 

 15.8 

 188.6 



41.2 



41.2 

 18.1 

 8.3 

 4.2 

 23.9 

 5.7 

 1.4 



Swimming 



change 



Counts per min 



Control 



Urethane 



65.0 

 57.2 

 15.7 



35.5 



6.6 



30.2 



143.6 



24.1 



152.4 

 8.2 

 2.0 

 4.2 



13.1 

 3.6 



13.7 



75.4 

 94.1 

 29.7 



38.6 



7.5 



34.1 



117.8 



36.0 



166.6 



10.8 



3.0 



5.4 



13.7 



4.0 



15.2 



change 



+16 



-f67 

 +89 



+ 9 

 + 1.5 

 + 13 



+24 



+50 



+ 9 

 +32 

 +50 

 +29 



+ 5 



+21 



+27 



* The ether-alcohol soluble fraction were transformed into barium carbonate previous to activity 

 measurement. Correspondingly the figures have to be multiplied by 7 • 7 to make them comparable with 

 the protein-activity figures. 



