Lead-exposure of neonatal rats through maternal milk : A confounded model

Lead-exposed neonatal rats are frequently used as a model for plumbism in children. In most studies,PPb is administered to the dam, and it is assumed that the pups are exposed to Pb primarily from the dam's milk. Rat pups, however, are coprophagic and begin to consume the maternal feces in their second postnatal week. This experiment was designed to determine whether the maternal feces are a significant source of Pb in pups exposed via the lactating dam. Dams were administered Pb as lead acetate (PbAc), either through their drinking water (500 ppm PbAc) or through twice daily intubations (3 mg PbAc/Kg body wt) from postpartum d 1 (P1) to P21 (P0=day of birth). Control dams were administered deionized water. The dams were housed with their litters in stainless-steel hanging cages with wire-screened bottoms. Litters of exposed and control dams treated through their drinking water had access to either Pb-containing or Pb-free maternal fecal matter for 2 h/d during the late lactation period. Half of the litters from intubated dams had continuous access to maternal feces throughout the lactation period, whereas access was curtailed at P14 in the other litters. Lead content of the feces from Pb-exposed dams ranged from 1000 to 5000 μg Pb/g wet wt. At P21, Pb concentrations were 2-4 times higher in blood, brain, bone, and liver of pups that had access to Pb-contaminated feces than in pups that were exposed to Pb primarily through the mother's milk. When estimating exposure levels in pups receiving Pb through the lactating dam, coprophagy and the high content of Pb in the dam's feces must be taken into consideration.