Increases in the concentrations of available iron in response to dietary iron supplementation are associated with changes in crypt cell proliferation in rat large intestine

High concentrations of iron in the diet have been shown to increase chemically induced colorectal tumors in rats. It is therefore important to understand the influence of dietary iron on the concentration of unabsorbed iron in the large intestine and its distribution between soluble and insoluble pools in the luminal compartment. We sought to investigate this issue and to establish whether iron modifies mucosal cell proliferation, which is thought to influence initiation and progression through the adenoma carcinoma sequence. In the first experiment, four groups of seven rats were fed diets at two concentrations of iron, 29 and 102 mg/kg, with or without the addition of 2.5 g phytic acid/kg. The concentrations of iron in the contents of the large bowel extractable with water ("free iron") or a buffered EDTA solution ("exchangeable iron") were determined. The concentration of freely soluble iron increased approximately 100% with iron supplementation in both the cecum and the colon, and there was an approximately five- to sixfold increase in exchangeable iron at both sites (