Influence of Dietary Protein Levels on the Acute Toxicity of Inorganic Mercury in Mice

Abstract

The influence of dietary protein levels on the acute toxicity of inorganic mercury (Hg) was investigated using mice fed a 24.8% protein diet (normal protein diet, NPD) or a 7.5% protein diet (low protein diet, LPD), and relationships between tissue susceptibility and both levels of Hg and metallothionein (MT) were examined. Twenty-four hr after administration of inorganic Hg, the plasma creatinine concentrations, an index of nephrotoxicity, increased in LPD-fed mice but not in NPD-fed mice at 5 mg Hg/kg, and in both dietary groups at 7.5 mg Hg/kg compared to the respective controls. However, plasma alanine aminotransferase (ALT) activities, an index of hepatotoxicity, increased in both groups only at 7.5 mg Hg/kg. Hg concentrations in the liver was higher in LPD-fed mice than in NPD-fed mice only at 5 mg Hg/kg, although dietary protein levels did not affect concentrations in the liver at 7.5 mg Hg/kg or in the kidney at both doses. MT concentrations were similar in the two dietary groups except for the liver, in which the lowered MT level was observed in LPD-fed mice only at 7.5 mg/kg. The present results suggest that dietary protein levels can modify the acute toxicity of singly administered inorganic Hg, at least in the kidney. It is also suggested that MT induction by toxic doses of inorganic Hg is suppressed by dietary protein deficiency, especially in the liver, but this difference would not lead to the variations in the toxicity or in the Hg retention at least within 24 hr.