Contributions of the Direct and Indirect Effects of Ionizing Radiation to Reproductive Cell Death

The contribution of indirect effects to cell damage is usually evaluated by using drying or freezing as well as exogenous compounds (scavengers) to trap water radicals. Up to the present there have been no attempts to quantify contributions of direct and indirect effects to radiation-induced cell inactivation from a collective of methods. Okada, in his monograph (1) summarizing the results obtained using different methods, concludes that in most cases direct effects are as important to cell death as indirect effects. However, he does not discuss the studies in which the indirect effect was either absent or amounted to 90%. Such a large variability (0-90%) was obtained for the same organism (2), which excludes the possibility of explaining it by different contributions of the indirect effect damage to various organisms. Besides, there is work (3) that shows increased radiosensitivity in dry cells. To explain these results one should suppose that the change in the radiosensitivity can be associated not only with water loss but also with other side effects which in terms of indirect effects are artifacts. Such a discrepancy in the data does not allow one to make even a qualitative estimation. To do this one should make a preliminary selection of methods and conditions for experiments where the artifacts would be minimized. We have tried to do this in our work.