Radiation-enhanced resistance to oxygen: a possible relationship to radiation-enhanced longevity

Shortly after gamma-irradiation, flour beetles (Oklahoma strain of Tribolium confusum) exhibited a decline in resistance to oxygen toxicity. Beginning about two weeks after irradiation, however, the LD50 exposure time in pure oxygen was much greater than that of nonirradiated beetles, and this enhanced resistance persisted for about 6 months. The magnitude of the enhancement was a function of dose, and decreased with increasing age at irradiation. These characteristics of a radiation-enhanced resistance to a stress are comparable to the characteristics of radiation-enhanced longevity in Tribolium, in that after irradiation mortality rate is less than that of controls for about 6 months, the magnitude of the effect is dose-dependent, and older beetles are refractory to the effect. Irradiation under anoxic conditions reduced the development of oxygen resistance to the same degree that it reduced acute radiation lethality, suggesting that the amount of biological damage is the critical factor. These results are discussed in terms of the "induced repair" theory of radiation-enhanced longevity of insects.