Factors influencing the transport of lead across the small intestine of the rat

Factors that affect the transport of environmentally relevant concentrations of the lead cation across various regions of the rat small intestine have been investigated using the everted sac preparation. In the absence of calcium or in the presence of excess hydrogen ions transport of lead is increased. Under normal conditions lead ions appear to passively diffuse across the intestinal epithelium via tight junctions. The interaction of lead with the intestinal tissue is markedly influenced by variations in pH, bile acid concentration, and luminal volume and supports the hypothesis that tissue phosphate ions are responsible for removing most of the free lead ions from the lumen. These observations suggest a model which (a) describes the mechanism of lead transport, (b) demonstrates that the intestinal tissue protects an animal against exposure to lead, and (c) predicts other conditions in which lead absorption may be markedly affected.