Effect of phosphate on the absorption and retention of lead in the rat

An inverse relationship between lead retention and dietary phosphate content has been known to exist for many years but the reasons for this association remained unknown. In rats, the manipulation of dietary phosphate content had no significant effect upon the absorption of lead from isolated gastrointestinal segments, but animals fed low phosphate content food had increased whole-body retention and bone deposition of intravenously administered tracer doses of radiolead. Intraluminal phosphate decreased the absorption of test doses of radiolead from the small intestine, possibly due to precipitation of lead in the gut lumen. Further, rats fed low phosphate diets absorbed increased quantities of an oral lead dose. Dietary phosphate deficiency may significantly increase body lead burdens by decreasing intraluminal lead precipitation and increasing lead retention, primarily in bone. Increased dietary phosphate, however, acts primarily to limit lead absorption.