The Gastrointestinal Absorption of Lead

Abstract

The intestinal absorption of orally dosed lead was studied in the rat using radiotracers. The main target organs for lead were liver and kidneys, though lead was widely distributed throughout soft and hard tissues. The overnight fasted rat absorbed approximately 30% of an oral dose of lead, whereas the fed animal absorbed only 5%. This suggested that food exerts a protective effect against lead toxicity. The kinetics of lead absorption were studied. The uptake of lead was seen to be directly proportional to the concentration of lead acetate dosed. No evidence of saturation of absorption was seen in any tissue. This suggests that lead enters the body via a diffusion mechanism. Agar replicas and mucosal scrapes were used to study the interaction of lead with the intestinal tissue. Significant amounts of lead were associated with apical glycocalyx and muscle layers. Although several factors (glucose, EDTA, iron competition, and amount of lead dosed) altered this interaction, no significant change in the amount of lead absorbed into the animal was observed. In the young rat, increased amounts of lead were observed in the intestinal wall and organs of the body cavity. This suggests that alternative mechanisms to those in adults exist. The small intestinal contents of lead dosed rats were partitioned into soluble and insoluble phases using ultracentrifugation. Gel permeation chromatography of the soluble (supernatant) phase indicated that it was mainly inorganic lead and lead bile salt complexes. Another minor species (presently unidentified) was produced in the fasted rat. This species may be protective in nature. The pellet (insoluble) phase was investigated using a sequential leaching technique. The pellet was shown to contain mainly lead carbonates, although other species (e.g. phosphates) were also present.