INDUCTION OF A CYTOGENETIC ADAPTIVE RESPONSE IN GERM-CELLS OF IRRADIATED MICE WITH VERY LOW-DOSE RATE OF CHRONIC GAMMA-IRRADIATION AND ITS BIOLOGICAL INFLUENCE ON RADIATION-INDUCED DNA OR CHROMOSOMAL DAMAGE AND CELL-KILLING IN THEIR MALE OFFSPRING

In earlier studies we have shown that either a single exposure or multiple exposures to a low dose of X-rays (0.05 Gy) induced a significant cytogenetic adaptive response in mouse germ cells, In this paper, a very low-dose rate (20 mu Gy/min) of chronic Co-60 gamma-irradiation was used to pre-irradiate mice for 40 days, Then, another 40 days later, these mice were treated with a subsequent large dose of X-irradiation, followed 24 h later by cytogenetic analysis of their spermatocytes. Analysis for radiation-induced DNA and chromosomal damage was also carried out in splenocytes, bone marrow cells and spermatocytes of the offspring of mice adapted by the low-dose rate of chronic gamma-irradiation. Results demonstrated that (i) cumulative gamma-irradiation (1.10 Gy) at the dose rate 20 mu Gy/min induced a marked cytogenetic adaptive response in the mouse germ cells (stem spermatogonia); (ii) the sensitivity of offspring's bone marrow cells and spermatocytes to 1.5 Gy X-ray-induced chromosome aberrations was not influenced by the low-dose radiation delivered to paternal germ cells; (iii) either constitutive or post-irradiation DNA repair capacity (UV-induced unscheduled DNA synthesis, UDS) was not modified in the offspring's splenocytes; (iv) the sensitivity of the offspring's splenocytes to radiation-induced cell killing was also not altered, These results suggest that low-dose radiation delivered to the male parents with a significant induction of cytogenetic adaptive response in their germ cell does not likely cause any risk of damaging effects to the offspring of those irradiated male mice.