Originally communicated in Nature, 164, 269 (1949). 



80. EFFECT OF X-RAYS ON THE INCORPORATION OF 

 CARBON-14 INTO ANIMAL TISSUE 



G. Hevesy 



From the Institute for Research in Organic Chemistry and the Pharmacological 

 Laboratories of the Karolinska Institute, Stockholm 



In a recent note^^\ it was shown that irradiation of rats with X-rays 

 diminishes very pronouncedly the rate of incorporation of carbon- 14 

 into desoxyribonucleic acid. Simultaneously, an enhanced incorpora- 

 tion of carbon-14 into the total proteins of the organs was observed. 

 This observation induced the investigation of the effect of irradiation 

 on the incorporation of carbon-14 in the whole tissue. 



About one microcurie of carbon-14 incorporated with the carboxyl 

 group of sodium acetate was injected subcutaneously into each of an 

 aggregate number of 180 one- to three-week-old rats and full-grown 

 mice, respectively. The animals were killed after the lapse of about eight 

 hours, and the radioactivity of the dried kidney, intestinal mucosa, 

 liver and muscle tissues was determined. Half the animals had been 

 previously irradiated for three minutes with a total dose of 950 r. (in 

 air), the voltage applied being 165 kV. A significant increase in the 

 incorporation of carbon-14 in every sample investigated was observed. 

 The figures in the accompanying tables show some of the results obtained 

 in experiments with rats (A) and mice (B). 



The above results indicate that, while the blocking of the formation 

 of nucleoproteins is probably the most conspicuous biochemical effect 

 of X-rays, the total metabolic pattern is influenced as well. 



A possible explanation of at least part of the enhanced incorporation 

 of carbon-14 into the tissue of irradiated animals is that in such animals 

 the basal metabolism is slightly decreased. Such a process would lead 

 to a higher activity-level in the organism which, in turn, would cause 

 an increased incorporation of carbon-14 into organic processes. 



Gould et alS^^ collected labelled carbon dioxide exhaled by full-grown 

 rats following the administration of labelled acetate. During the first 

 hour, they found a 50 per cent reduction in the specific activity of carbon 

 dioxide every 15 minutes, and interpreted this observation as being 

 primarily a dilution of isotopic carbon dioxide of the body fluids with 

 non-isotopic carbon dioxide of metabolic processes. In the course of 



