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

The radioprotective ability of melatonin was investigated in mice exposed t o an acute whole-body gamma radiation dose of 815 cGy (estimated LD50/30 do se). The animals were observed for mortality over a period of 30 days follo wing irradiation. The results indicated 100% survival for unirradiated and untreated control mice, and for mice treated with melatonin or solvent alon e. Forty-five percent of mice exposed to 815 cGy radiation alone, and 50% o f mice pretreated with solvent and irradiated with 815 cGy were alive at th e end of 30 days. Irradiated mice which were pretreated with 125 mg/kg mela tonin exhibited a slight increase in their survival (60%) (p = 0.3421). In contrast, 85% of irradiated mice which were pretreated with 250 mg/kg melat onin 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 re served.