EFFECT OF X-RAYS ON THE RESORPTION 

 RATE OF INJECTED NaH^COg IN MICE 



A. FoRSSBERG and G. Hevesy 

 Institute of Radiophysics and Institute of Organic Chemistry, Stockholm 



In this short version of our paper ^ we present evidence for an X-ray effect in 

 mice, which have been given a total body irradiation of 2,000 r immediately 

 followed by an intraperitoneal injection of NaH^^COg. Forty mg of 

 bicarbonate were injected and this gave 7,000 counts/min /mouse in our in- 

 strument and about 5 per cent of the total activity was assayed. The mean 

 life-time of the bulk of the circulating bicarbonate ions in the l^ody of the 

 mouse is a few minutes onl) , and any change in the rate of resorption will be 

 reflected in a corresponding change in the amount of ^^COg exhaled within 

 a few minutes or even seconds after the injection. 



In the first set of experiments we started the collection of exhaled carbon 

 dioxide about 10 minutes after injection of the isotope and followed this 

 process for one hour at 10-min intervals. We ascertained that irradiated 

 mice exhaled approximately 25 per cent more ^^COa than controls combined 

 with a slight decrease (some 10 per cent) in the output of the total amount 

 of COg. The latter fact had been noticed by us previously^. The en- 

 hanced exhalation of ^^COg might be expected to run parallel with a 

 smaller amount of residual ^''C in the body of irradiated animals. Analyses 

 of controls and irradiated mice about half an hour after the injection showed, 

 however, that the activity of the homogenized and dried tissue did not vary 

 appreciably. 



The explanation seemed to be that irradiated mice exhale ^^COg at a 

 markedly decreased rate for a short period immediately after the injection 

 of the bicarbonate, leaving these animals with an increased pool of ^'^C 

 some 10-60 min afterwards. Experiments to that end, using a special 

 device for collection of carbon dioxide immediately upon the injection of 

 NaH^'^COg, showed, that in the first 4 min of the experiment during which an 

 appreciable percentage of the injected ^^COo is exhaled, the controls give 

 off more ^-^COg (45 per cent) than the irradiated animals (29 per cent) and 

 more ^^C being preserved in the exposed animals, more ^^COg is exhaled in 

 the later stage of the experiment. The activity expired during the first 

 minute, including the 6 sec taken for the injection in these experiments, 

 was found to be only 43 per cent of that of the control. This indicates that 

 the X-ray effect on the process of resorption of bicarbonate and the intrusion 

 of •"^^COg into the alveolar space is very marked. 



The slower exhalation of ^^COg by the exposed animals shortly after 

 injection of the labelled bicarbonate could be due to a depressed resorption 

 or /and disturbances of the blood circulation. To investigate how far the 

 latter is the case we injected bicarbonate into the tail vein and collected the 

 carbon dioxide in 2-min intervals starting immediately after injection. Only 



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