Protective effect of melatonin on methylmercury-induced mortality in mice

Effect of melatonin on the mortality in methylmercury chloride (MMC)-intoxicated mice was evaluated. Mice were given MMC in the diet (40 mgHg/g) with or without melatonin in drinking water (20 mg/ml) for 5 weeks. In the control group, given MMC alone, 4 of 10 mice began to show neurological signs (e.g., abnormal righting reflex, staggering gaitfallen and posture on its side) concomitant with loss of body weight 4-7 days before death. This group also showed 60% of survival rate on the 35th day. However, the treated group, concomitantly given melatonin, showed a 100% of survival rate on the 35th day, although 1 of 10 mice began to show the neurological signs on the 33rd day. The level of thiobarbituric acid reactive substance in the brain, as an indication of oxidative damage, showed a significant u decrease in the treated group compared with the control group. Thus, the 100% survival rate in the treated group may be partly due to antioxidative effect of melatonin on the MMC induced neurotoxicity. (C) 2000 Tohoku University Medical Press.