Synergistic Effect Versus Radioadaptive Response: Possible Implications of Such a Response in the Estimation of Risks of Low-level Radiation Can be More Problematical

There is growing evidence for the existence of radioadaptive response. Furthermore, some investigators have reported entirely negative results in individuals with chromosome instabilities as well as healthy persons. In our studies we found a young healthy donor who showed no adaptive response in all of our experiments. In addition, he showed a severe hypersensitivity to subsequent irradiation after a common adapting dose (synergistic effect). To assess whether the induction of such a synergistic response and lack of radioadaptive response is a temporary situation or not, we evaluated the frequency of radiation-induced chromosome aberrations during a 6 month follow up. Peripheral blood lymphocytes of this donor were exposed to an adapting dose of 5 or 10 cGy X-rays followed by a challenge dose of 2 or 3 Gy X-rays with different radiation qualities. This donor showed no adaptive response in all of the experiments. Furthermore, considering the induction of a severe synergistic effect in some experiments, it may be concluded that the induction of such a severe response is a temporary situation. Despite the fact that we do not know the frequency of such individuals in the population who show such an extraordinary synergistic effect, it may be concluded that possible implications of radioadaptive response in the