The Gastrointestinal Absorption of Lead

Abstract

The transport of environmentally relevant concentrations of the lead cation has been investigated using the everted sac preparation. Only a small percentage of lead was transported into the serosal compartment but there was a rapid and massive uptake on to the tissue. There was no Significant difference in the amount of lead transported across different regions of the small intestine. Both rate of transport into the serosal compartment and the tissue uptake increased linearly with increased concentration of lead. Little evidence for saturation of serosal transport or tissue uptake was found. Lead transport into the serosal compartment appeared to be related to water movement but was little affected by changes in glucose concentration, temperature or anoxic conditions. In the absence of calcium ions, or in the presence of excess hydrogen ions, transport of lead into the serosal compartment was increased, therefore lead may passively traverse the intestinal epithelium via the zonulae occludentes. Increased lead transport may proceed by an intracellular route after interaction with a chelating agent. The interaction between dead ions and the intestinal tissue was extremely tenacious and displayed characteristics of covalent bonding. Variations in pH markedly influenced the lead-tissue interaction which Supports the hypothesis that tissue phosphate ions are responsible for removing lead ions from the lumen. Excess bile salts and DTPA decreased the lead-tissue interaction whilst decreased luminal volume increased the interaction. The observations permit the development of a simple model which a) elucidates the mechanism of lead transport, b) demonstrates that the intestinal lumen protects the animal against excessive exposure to lead by governing the quantity of lead that appears in blood, c) predicts the conditions in which lead absorption may be markedly affected.