Sex Difference in the Influence of Dietary Protein Deficiency on the Fate of Methylmercury in Mice and Rats

We investigated sex difference in the influence of dietary protein deficiency on the fate of methylmercury (MeHg) using both sexes of C57BL/6N mice and Wistar rats to determine the universality of the influence. One day after oral administration of MeHg (20 mol/kg), regardless of sex and species, urinary Hg excretion was suppressed by dietary protein deficiency, whereas fecal excretion was not affected. At that time, tissue Hg concentrations in both sexes of the specified species were similarly influenced by dietary protein deficiency except for the gonads, although the influence on Hg concentration in each tissue was different between species. Regardless of sex, dietary protein deficiency resulted in the following alterations: in mice, the brain Hg concentration increased but the concentrations in the liver, kidney, blood and plasma were not affected, and in rats, Hg concentrations in the liver and blood increased but the renal concentration decreased with similar concentrations in the plasma and brain. Hg concentration in the testes was enhanced in mice but suppressed in rats by dietary protein deficiency, whereas that in the ovary was not affected in either species, suggesting that Hg accumulation in the gonads would be more changeable in males than in females by dietary protein deficiency. These results suggest that, regardless of sex, dietary protein deficiency similarly influences the fate of MeHg, except for the gonads. It is also suggested that a decrease in urinary excretion of MeHg by dietary protein deficiency might be universal.