Role of the proximal colon in mineral absorption in rats with and without ferropenic anemia

We studied the effects of the deficiency on the absorption of different dietary sources of iron in vivo (non-heme, heme, and equal of both forms), and investigated the interactions between iron and calcium, phosphorus, magnesium, copper and zinc in the proximal colon of control and iron-deficient rats. Three perfusion solutions containing a different source of iron were used: solution 1, ferric citrate; solution 2, hemoglobin; solution 3, equal parts of ferric citrate and hemoglobin. We also tested the same perfusion solutions with 2,4-dinitrophenol (2,4-DNP), an inhibitor of oxidative phosphorylation (solutions 1-I, 2-I and 3-I). In control rats we observed three mechanisms of iron absorption; passive for soluble iron salts, active receptor-mediated for inorganic Fe complexes, and active receptor-mediates for heme iron. In anemic rats iron absorption was greater than in controls, expect after perfusion with solution 2 (containing hemoglobin). Absorption increased as a results of the passive mechanism. The active component was influenced by the depletion of heme receptors under severe iron deficiency. The absorption of calcium, phosphorus, magnesium, copper and zinc was greater in iron-deficient animals than in the control group. After perfusion with solution 2 or 3, calcium copper and zinc absorption were lower than after solution 1. We conclude that ferropenic anemia leads to increased absorption by the proximal colon of all minerals studied. This increase is due mainly to the passive route of absorption.