INFLUENCE OF DIETARY-PROTEIN LEVELS ON THE ACUTE TOXICITY OF METHYLMERCURY IN MICE

The influence of dietary protein levels on the acute toxicity of methy lmercury (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 m ice, all mice died at a medium or high dose (80 or 120 mu mol/kg, resp ectively) within 16 or 7 days, respectively, but not at a low dose (40 mu mol/kg) in both dietary groups. Although no difference was observe d in the survival rate at a medium dose, NPD-fed mice died earlier des pite lower brain Hg than LPD-fed mice at a high dose. Accordingly, dea th, in our observations, could not be due to neural damage by MeHg. Wh en a high dose of MeHg was administered to mice, plasma aspartate amin otransferase 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 the reaso n for the shorter survival period in NPD-fed mice. Since plasma creati nine increased within 24 h after MeHg administration at a medium or hi gh dose, renal dysfunction could be a major factor in death. The prese nt results suggest that susceptibility to acute MeHg toxicity was high er in NPD-fed mice than in LPD-fed mice, possibly due to the differenc e in hepatic susceptibility.