Influence of dietary protein levels on the acute toxicity of methylmercury in mice.

The influence of dietary protein levels on the acute toxicity of methylmercury (MeHg) was investigated using C57BL/6N male mice fed either a 24.8% protein diet (normal protein diet, NPD) or a 7.5% protein diet (low protein diet, LPD). When MeHg was administered to each group of mice, all mice died at a medium or high dose (80 or 120 mumol/kg, respectively) within 16 or 7 days, respectively, but not at a low dose (40 mumol/kg) in both dietary groups. Although no difference was observed in the survival rate at a medium dose, NPD-fed mice died earlier despite lower brain Hg than LPD-fed mice at a high dose. Accordingly, death, in our observations, could not be due to neural damage by MeHg. When a high dose of MeHg was administered to mice, plasma aspartate aminotransferase and alanine aminotransferase activities increased in NPD-fed mice but not in LPD-fed mice in spite of similar hepatic Hg levels. Therefore, the higher susceptibility of the liver could be reason for the shorter survival period in NPD-fed mice. Since plasma creatinine increased within 24 h after MeHg administration at a medium or high dose, renal dysfunction could be a major factor in death. The present results suggest that susceptibility to acute MeHg toxicity was higher in NPD-fed mice than in LPD-fed mice, possibly due to the difference in hepatic susceptibility.