Damage-repair kinetics and early adaptive response induced by gamma rays in murine leukocytes in vivo.

The kinetics of damage induction and repair at different doses, and the adaptive response induced by gamma ray exposure were determined in murine leukocytes in vivo. The adaptive response was determined after an adaptive dose of 0.01 Gy and a challenge dose of 1.0 Gy administered 60 min later. DNA damage was measured by the single cell gel electrophoresis. Results indicate there is an early and efficient repair process that acts even during the exposure to radiation, which is able to reduce 80% of damaged cells. Later, an increase in damaged cells occurs, which seems to represent the breaks induced during the repair of other kinds of lesions. This suggests that mouse cells are genetically adapted to repair this kind of damage. It was found that the adaptive pretreatment reduces the percentage of damaged cells caused by the challenge dose to one third, and diminishes the damage produced during the late repair. This indicates that the early adaptive response is caused by the induction of a process that protects DNA from damage induction, i.e., synthesis of substances that scavenge free radicals.