Evidence for a Humoral Factor Influencing Iron Absorption

Abstract

A series of studies was carried out to determine the effect of various serum preparations on iron absoprtion in the rat. Serum obtained from normal or previously iron-repleted and iron-depleted rats was injected intravenously into normal rats, and the intestinal transport of of iron determined utilizing isolated intestinal loops in vivo and everted duodenal gut sacs in vitro. In normal rats injected with serum from iron-loaded rats there was a significantly decreased absorption of radioactive iron in intestinal loops as well as a decreased mucosal to serosal transfer of radioactive iron in duodenal gut sacs. The factor in serum from iron-loaded rats causing decreased iron transport was found to be heat-stable. Three additional observations indicated that this defect in iron transport was not due to the infusion of iron per se. First, there was no increase in the nonheme iron content of the gut after injection of iron-repleted serum. Second, the intravenous injection of 15 µg of iron as FeSO4, similar to the amount of iron contained in an injection of iron-loaded serum, did not cause decreased absorption of radioiron from intestinal loops. Third, there was no increase in the serum iron level or saturation of transferrin in normal animals given iron-loaded serum. It was also observed that the defect in iron absorption induced by iron-loading rats with iron dextran could be partially corrected by the intravenous injection of normal serum or serum from iron-deficient rats. It is postulated that the serum injections may have resulted in dilution of a humoral inhibitory factor. The data obtained indicate that humoral stimulation and depression of iron absorption is demonstrable by the injection of normal or iron-deficient serum into iron-loaded rats and the injection of iron- loaded serum into normal rats. These observations suggest that a humoral mechanism may participate in the regulation of inorganic iron absorption in the rat.