The Relationship between the Anoxic Sensitivity and the Extent of Sensitization by Nitrous Oxide

Summary Nitrous oxide reacts during irradiation to increase the yield of ·OH, a radical many believe to be a major cause of lethality. Logically, one would expect N2O to be a radiation sensitizer. In some instances it is, while in others it is not. In some cases we can explain why N2O fails to sensitize; factors such as dose rate, cell concentration, buffer composition and ionic strength all influence when N2O will sensitize and, if it sensitizes, by what magnitude. Based on the results presented here with multiple strains of procaryotic and eucaryotic cells, we believe the anoxic sensitivity is another critical factor that governs whether N2O will sensitize. Our data, with data from the literature, show a relationship between the anoxic sensitivity and the N2O enhancement ratio. N2O does not sensitize in vitro unless the anoxic sensitivity (inactivation constant, k) is less than ∼ 0·2 daGy−1.