The effect of oxygen on cellular survival and recovery after radiation.

Abstract

Chinese hamster cells were exposed to X radiation in argon with an oxygen content either less than 2 ppm, considered anoxic conditions, or 120 or 400 ppm, considered hypoxic conditions. The survival curve after irradiation with exposures of 800, 1,200 and 1,600 R in anoxia was exponential. In comparison, the survival curve of cells irradiated in hypoxia had an increased regression and an increased extrapolation number at zero dose. When treated with exposures of 150, 300 and 450 R in 120 ppm oxygen, the number of survivors was about 10 per cent larger than when the exposures were delivered in anoxia. A split-dose ratio close to unity was calculated when the survival after a single exposure of 800 or 1,600 R in anoxia was related to the survival after the same doses delivered in two equal fractions with 18-hour intervals. When treatment with the same doses was made in the presence of oxygen, the survival ratio was increased to an extent comparable to the increase of the corresponding extrapolation numbers. When 3 × 300 R was delivered with three-hour intervals in hypoxia, the survival was increased in relation to the survival after a similar treatment in anoxia, and also in relation to the survival after a single anoxic or hypoxic treatment with the same total dose. The change in the extrapolation number and the extent of recovery was closely related to the change in the oxygen consumption of cells at the particular oxygen concentrations. The relationship between oxygen concentration and change in the survival regression could be described by the formula suggested by Howard-Flanders and Alper (1957). It was concluded that oxygen may play a dual role in regard to radiation survival: on the one hand it sensitises the cells by enhancing the radiation damage, and on the other hand it protects them by permitting the oxidative metabolism which probably provides the energy required by the repair processes.