Melatonin and protection from whole-body irradiation: Survival studies in mice

The radioprotective ability of melatonin was investigated in mice exposed to an acute whole-body gamma radiation dose of 815 cGy (estimated LD(50/30) dose) . The animals were observed for mortality over a period of 30 days following irradiation. The results indicated 100% survival for unirradiated and untreated control mice, and for mice treated with melatonin or solvent alone. Forty-five percent of mice exposed to 815 cGy radiation alone, and 50% of mice pretreated with solvent and irradiated with 815 cGy were alive at the end of 30 days. Irradiated mice which were pretreated with 125 mg/kg melatonin exhibited a slight increase in their survival (60%) (p = 0.3421). In contrast, 85% of irradiated mice which were pretreated with 250 mg/kg melatonin were alive at the end of 30 days (p = 0.0080). These results indicate that melatonin (at a dose as high as 250 mg/kg) is non-toxic, and that high doses of melatonin are effective in protecting mice from lethal effects of acute whole-body irradiation. (C) 1999 Elsevier Science B.V. All rights reserved.