New considerations of the oxygen effects in radiation biology.

The original demonstration in the bacterial spore of the multiple actions of oxygen in modifying the responses of cells to ionizing radiation has now been verified in mammalian systems, pointing up the need for separate inquiry into each of the several components if the responses of mammalian cells are to be understood. We have provided physico-chemical explanations for only two of the four (at least) oxygen elements recognized in the spore: the reaction of diatomic oxygen with organic free radicals in dry spores; and an action of the hydroxy radical (OH) in spores at low O2]. This paper will discuss newly recognized features of the oxygen responses that could reveal the nature of the other components. It will examine modulation of response by oxides of nitrogen, the similarities and differences among them and explanations for them that suggest further experiment, the importance of concentration of additive in determining both quantity and quality of response, and a general model that explains sensitizer action in terms of inhomogeneous chemistry.