Pharmacodynamics of methyl mercury in the murine maternal/embryo: Fetal unit

Abstract

To investigate fetal uptake of methyl mercury (MeHg) during organogenesis, a single dose of MeHg (5 mg of Hg/kg), 100 μCi 203 Hg/kg in 0.13 m NaCl, 0.01 m Na 2HPO 4, pH 7.4) was administered sc to pregnant Swiss-Webster CFW mice on Days 7 through 13 of gestation. Fetal accumulation of mercury increased with fetal age at time of administration at least up to Day 13 of gestation. MeHg administered on Days 10 through 13 of gestation produced fetal mercury concentrations higher than maternal blood concentrations by 7 (injected on Day 10 or 11) or 5 (injected on Day 12 or 13) days post administration. Peak fetal mercury concentrations were reached 3 days post administration, averaging 4.8 mg/kg in animals injected on Day 13 of gestation. Placental mercury concentrations were always equal to or higher than maternal blood mercury concentrations. An increase in maternal liver net elimination rate (1.3 μg of Hg/day when MeHg was administered on Day 7; 3.4 μg of Hg/day when administered on Day 13) was associated with the increased fetal sequestration of MeHg during later gestational stages. Maternal blood elimination rates increased slightly throughout the same period. To determine the uptake of mercury via suckling, offspring of dams given MeHg on Day 12 of gestation and control dams were cross-fostered. All tissue mercury concentrations of MeHg × MeHg offspring were nearly identical to those of the dams at 10 and 21 days postpartum. Tissue mercury concentrations in MeHg × Sal offspring ( in utero mercury exposure) were 15 to 30 times greater than in Sal × MeHg offspring (suckling mercury exposure), indicating far greater mercury transfer in utero.