Kinetic Observations in Neonatal Mice Exposed to Lead via Milk

Abstract

The absorption and disposition of lead in blood was examined in 10-day-old suckling mice exposed via milk. Lactating dams were administered a single intravenous injection of 0.05 mg Pb (2.5 mCi203Pb)/kg body wt. Lead concentrations in blood of the suckling offspring were measured for 10 days after administration to the dams. Maximum blood lead concentrations in the pups were recorded between 50 and 74 hr after dams’ administration despite the fact that the majority of the lead dose to the sucklings was delivered within 24 hr after dams’ administration. Kinetic analysis of pups’ blood lead data revealed a rate-limited absorption in the suckling pups with an absorption half-life of approximately 17 hr in the pups. This delayed absorption is most likely due to a retention of casein-bound lead in the ileal mucosa which has a high pinocytotic activity of dietary proteins in infant rodents. The present results also indicated that the distribution of lead to the peripheral tissues in the suckling mice was different than that of adults. The conflicting evidence on whether milk enhances or inhibits the absorption of lead in infant rodents may thus be explained by measurements of lead absorption at different time periods after administration to the animals. It is also suggested that the milk diet is one reason for the increased absorption of lead seen in immature rodents.