Availability to rats of iron in ferric hydroxide polymers

Availability to rats of Fe in isolated ferric hydroxide polymers was assessed. Polymers were prepared by hydrolyzing an 59Fe-labeled ferric nitrate solution with base (KHCO3). After isolation by gel filtration, the polymers were characterized by spectrophotometric, dialysis, and ultracentrifugation methods. In a split-plot design experiment, Fe-adequate (Hb 11.4-14.0 g/dl) or Fe-deficient (Hb 4.7-9.6 g/dl) male Sprague-Dawley rats (10/treatment) were dosed by stomach tube with one of the following 59Fe-labeled solutions: polymers, Fe(NO3)3 (low-molecular-weight control), polymers + citrate, or Fe(NO3)3 + citrate. As expected, Fe-deficient animals absorbed more Fe than adequate animals (P less than 0.01). There was no difference in absorption of Fe between polymers and low-molecular-weight control doses (P greater than 0.05). In Fe-adequate animals, citrate significantly depressed the uptake of Fe both from Fe(NO3)3 and polymers. These results indicate 1) that polymerization of Fe species prior to ingestion is not a likely means by which Fe is rendered unavailable and 2) that the effect of citrate on Fe absorption may depend on the Fe status of the animal.