Lactational exposure to methylmercury in the hamster

Abstract

Syrian Golden hamster dams were administered 203Hg-labelled methyl mercury (MeHg; 1.6 mumol/kg) 1 day after parturition and milk was collected twice during the 1st week. The excretion of 203Hg in milk and the uptake, retention and tissue distribution of 203Hg in the pups was studied using gamma counting. The fraction of inorganic Hg in milk and in the kidneys of the pups was determined following separation of inorganic Hg and MeHg by ion exchange chromatography. The concentration of 203Hg in milk on the 1st day after MeHg administration was 0.12 nmol/g. 203Hg was mainly (80-90%) excreted as MeHg during the first 6 days of lactation. The whole body and tissue concentration of 203Hg in the pups increased for 10-15 days and decreased thereafter. The content of 203Hg in the pelt and the fraction of inorganic Hg in the kidney increased throughout the study period (4 weeks). The excretion of MeHg in milk corresponded to at least 5% of the dose administered to the dam. Our study demonstrates that breast milk may be a significant source of MeHg exposure during the critical neonatal period.

Transplacental and Lactational Exposure to Mercury in Hamster Pups after Maternal Administration of Methyl Mercury in Late Gestation

“…In the present study as well as in our previous studies Nordenhall et al 1995), an increasing amount of 203Hg was found in the pelt (>So% of body burden after 14 days of age). This can largely explain the high whole-body retention of 203Hg in the pups.…”

“…(1986) and our previous findings(Nordenhall et al 1995).The content of 203Hg in the pups one day postpartum in relation to the dose of 203Hg-MeHg or 203HgC12 administered to the dams is presented in table 1. The brain to blood concentration ratios of 203Hg in eight of the MeHg-treated dams in relation to time after parturition are shown infig.…”

“…In a previous study (Nordenhall et al 1995), in which the dams were administered MeHg one day post parturn, the lactational transfer (estimated by the same procedure) was 4.7% of the administered dose. = 0.46%, range: 1.2-2.4, N=9 litters) of the administered dose.…”

Metabolism of Mercury in Hamster Pups Administered a Single Dose of 203Hg‐Labeled Methyl Mercury

“…Radiolabeled MeHg was synthesized according to Naganuma et al (1985) using 203Hg-labeled HgC12 (0.24 mCi/pmol, Amersham, UK) and methylcobalamin (Sigma Chemical Co, St. Louis, MO, U.S.A.) as previously described (Dock et al 1994). The solution of 203Hglabeled MeHg in saline was added to stable MeHgCl (Merck-Schuchardt, Hohenbrunn bei Miinchen, Germany), dissolved in saline, to a final specific activity of 30 pCi/pmol.…”

“…Seven-day old hamster pups (37 animals from six different litters) with a mean body weight of 6.8 g (range 5.1-8.5 g) received a single subcutaneous injection of 203Hg-labeled MeHg, 0.4 nmoVg body weight (0.060.07 VCiianimal), in the shoulder region. The administered dose corresponded to the concentration of Hg found in foetal hamsters one day before birth, when the dams were administered a single dose of MeHg (1.6 pmol/kg) six days previously (Dock et al 1994). One or two animals from each litter were sacrificed by sodium pentobartibal anaesthesia (Mebumal, Nordvacc, Sweden) and exsanguination (decapitation) 2, 7, 14, 21 or 28 days after administration.…”