Effects of melatonin on apoptosis of lymphocytes induced by ionizing radiation in mice

AIM: To explore the effect of melatonin (MLT) on the apoptosis of thymocytes and splenocytes in mice induced by ionizing radiation and its mechanism. METHODS: The percentages of apoptotic bodies and the DNA lytic rates of thymocytes and splenocytes in mice in vitro and in vivo were detected with flow cytometry and fluorospectrophotometry, respectively. RESULTS: The apoptosis of mouse thymocytes and splenocytes in vitro increased with significant dose-dependence in 0.5-6.0 Gy X-irradiation. When MLT of 2 mmol·L^-1 was added into thymocytes or splenocytes in vitro before irradiation with 0.5-6.0 Gy X-rays, the percentages of apoptotic bodies and the DNA lytic rates all decreased significantly as compared with those in the irradiation group. The percentages of apoptotic bodies in these two kinds of cells were 86.25% and 89.22% of those in the irradiation group, respectively, and the DNA lytic rates were 87.23% and 89.16%, respectively. When MLT was injected into intraperitonium in mice 60 min before whole-body irradiation with 2 Gy X-rays, the percentages of apoptotic bodies and the DNA lytic rates were significantly lower than those in the irradiation group, and near or lower than those in the sham-irradiation group. MLT of 0.1-2.5 mg/kg decreased the lymphocyte apoptosis, but without significant dose-dependence. CONCLUSION: The protective effects of MLT on mouse lymphocytes damaged by irradiation in vivo were obvious than those in vitro.