Iron deficiency: improved exercise performance within 15 hours of iron treatment in rats.

We tested the hypothesis that a very rapid improvement in exercise performance of iron-deficient rats after treatment with iron might reveal a rate-limiting role of ionic iron as an enzyme cofactor in energy metabolism. Rats were given iron-deficient or control diets after weaning at 21 d of age and intraperitoneal iron dextran (50 mg/kg) at 45 d of age. Time to fatigue during an easy walking exercise (endurance) was measured 15 and 18 h after iron dextran or saline injection. Endurance increased more than threefold compared to the saline-treated, iron-deficient animals without a significant change in hemoglobin concentration. This prompt improvement suggests that lack of cofactor iron might play a metabolically important role in impairing exercise performance in the severely iron-deficient rat.