Effects of iron on the absorption and retention of lead.

An inverse relationship between lead retention and dietary iron content has been suspected for many years, but the reasons for this association remained unknown. In rats, the state of body iron repletion had significant effects on the absorption of lead but no effect on lead excretion. Intraluminal iron decreased the absorption of test doses of lead from the small intestine in a dose-related manner. We postulated that this occurred because the two metals competed for similar binding sites on intestinal mucosal proteins which were important in the absorptive process. In vivo, both lead and iron bound to two heat-stable intestinal mucosal fractions, particularly the higher-molecular-weight fraction. Addition of iron to test doses of lead markedly diminished the amount of lead bound by the high-molecular-weight fraction. Further investigation revealed that this fraction, with a molecular weight of approximately 370,000, bound both lead and iron. Shared binding sites on this protein may explain why dietary iron decreased lead absorption and iron deficiency increased it.