DEMETHYLATION AND PLACENTAL-TRANSFER OF METHYL MERCURY IN THE PREGNANT HAMSTER

The demethylation and placental transfer of methylmercury (MeHg) was studied in Syrian Golden hamsters administered a single oral dose of Hg-203-labeled MeHgCl, 1.6 mu mol/kg body weight, on day 2 or 9 of gestation and sacrificed 1 day before expected parturition. In order to evaluate the role of demethylation for transplacental transport of MeHg, four hamsters were administered Hg-203-labeled HgCl2 intravenously on day 9 of gestation. The mean biological halftime of Hg-203 in animals administered radiolabeled MeHg was 7.7 days and the fecal route was the main excretory pathway. The fetal content of Hg-203 in hamsters administered radiolabeled MeHg on gestational day 2 or 9 corresponded to 1.3% and 4.6% of the administered dose, respectively, The distribution of Hg-203 in the fetus was more even than in the dam and the concentration of Hg-203 in the fetal brain, liver and kidney was similar to that of the placenta. Inorganic Hg was found in maternal liver (18% of total Hg), kidney (31%) and placenta (21%) and fetal liver (3%). The amount of inorganic Hg-203 in fetal liver corresponded to about 0.015% of the dose administered to the dam as MeHg. When hamsters were administered (HgCl2)-Hg-203 by intravenous injection on day 9 of gestation, the concentration of Hg-203 in fetal liver corresponded to 0.03% of the administered dose. The inorganic Hg-203 detected in fetal liver after maternal exposure to MeHg was probably due to demethylation of MeHg in the dam and transplacental transfer of inorganic Hg.