Melatonin Reduces Radiation Damage to the Spleen and Increases Survival When Administered before and after the Exposure of Mice to X-ray Radiation

— Damage to the spleen was studied after the effect of X-ray irradiation of the whole body of mice at a dose of 5 Gy and modulation of this damage by the administration of melatonin (MEL). The effect of MEL on the survival of mice irradiated at doses of 5 and 9 Gy was determined simultaneously. At the same time, the nuclear DNA damage and repair, levels of malondialdehyde (MDA), reduced glutathione (GSH), and the frequencies of micronuclei induction in mouse bone marrow cells were estimated. The results demonstrated that post-irradiation DNA repair in the spleen of mice receiving MEL occurs more actively as compared with that in the control groups. At the same time, the effect of MEL modulation is more pronounced in the tissues of mice that were injected with MEL after irradiation. The levels of MDA are sharply reduced in the spleen of mice injected with MEL, while the content of GSH increases significantly. A decrease in the frequency of micronuclei is observed in irradiated mice injected with MEL. The results on survival of mice demonstrated that MEL provides efficient protection against X-ray irradiation. The observed radiation protection of MEL is more pronounced during its administration to mice after irradiation at doses of 5 and 9 Gy. Thus, MEL reduces radiation damage to the spleen and increases the survival of mice when administered before and after irradiation.