THE INFLUENCE OF OXYGEN ON 

 RADIATION EFFECTS 



H. Laser* 



Molteno Institute, University of Cambridge 



It is well established that the extent to which a variety of 

 cells may be damaged by ionizing radiation is greater if the 

 irradiation takes place in the presence of oxygen than if it 

 takes place under anaerobic conditions. This applies equally 

 to plant, insect and mammalian tissues (Barron, 1952; 

 Hollaender, 1952; Hollaender, Baker and Anderson, 1951; 

 Hollaender, Stapleton and Martin, 1951; Gray, 1953; Gray 

 et al.y 1953), and the mechanism of this so-called "oxygen 

 effect", which is not yet fully understood, may also hold the 

 key to the mode of action of ionizing radiation in general. 



Broadly speaking, two disciplines, with their sometimes 

 widely varying train of thought and approach, have attempted 

 to explain the oxygen effect, those of the physicochemist and 

 the biochemist. 



The former maintains that oxygen acts per se, e.g., that its 

 mere presence modifies the nature of the chemical inter- 

 mediates formed along the tracks of ionizing particles, thereby 

 apparently producing greater though not well defined damage 

 to the cells ; or it thinks in terms of strongly oxidizing radicals, 

 such as HO2, and of HgOg, which are only formed in presence 

 of dissolved oxygen, as causing increased radiosensitivity. 



The difficulty in accepting a purely physicochemical ex- 

 planation lies, at least to my mind, in the fact that it creates 

 an unwarranted barrier between chemical and biochemical 

 causes. It fails to take into account the fact that the state of 

 the affected "entity " in the cell may determine its response to 

 irradiation. It furthermore assumes that oxidizing radicals or 



* Member of the Scientific Staff of the Medical Research Council. 



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