Sex and age differences in mercury distribution and excretion in methylmercury-administered mice

Sex differences in mercury distribution and excretion after single administration of methylmercury chloride (MMC, 5 mg/kg) were studied in mice. A sex difference in urinary mercury excretion was found in sexually mature mice (age of 7 wk) of C57BL/6N and BALB/cA strains. Males showed higher mercury levels in urine than females, though no significant difference was found in fecal mercury levels 24 h post exposure to MMC. The higher urinary excretion rates in males accounted for significant lowering of mercury levels in the brain, liver, and blood, but not in the kidney, which showed higher values. At 5 min, however, these sex difference was found only in the kidney, showing higher levels in males. Changes in mercury distribution with time were studied in C57BL/6N mice. The brain mercury increased in both sexes up to 3 d, and decreased only in males on d 5. Liver and blood mercury decreased with time in both sexes, and these were constantly higher in females than in males. Renal mercury in males decreased to similar levels to females on d 3. The sex differences at various ages were studied with C57BL/6N mice 24 h after dosing. Two-week-old mice, the youngest in this study, did not show significant sex difference in the mercury distribution and excretion, and their urinary mercury levels were much lower as compared to the older mice. Then, urinary mercury excretion in both sexes increased at 4 wk of age and then decreased at 45 wk of age. At 4, 7, 10, and 45 wk of age, males showed higher urinary mercury levels than females. These studies demonstrated sex and age differences in the mercury distribution and urinary excretion after methylmercury administration in mice. From these findings, it has been suggested that urinary mercury excretion may be related to sex hormones, especially androgens.