Studies on Iron Absorption. Intestinal Regulatory Mechanisms*

Abstract

Studies on rate and site of iron absorption were performed during the early rapid phase of iron absorption by the use of closed intestinal loops in anesthetized but otherwise intact rats with varying body iron stores. With the use of Fe59 and whole body counting, it was possible to determine total iron absorbed from intestinal lumen and iron transferred to carcass during accurately time absorption periods. The findings suggest that iron is absorbed by an active transport mechanism comprised of at least two steps (1) mucosal uptake of iron from lumen and (2) mucosal transfer of iron to carcass. Both steps varied inversely with the state of body iron stores. Compared to mucosal uptake, mucosal transfer was more restricted to duodenum, more affected by changes in body iron stores and prefeeding iron, and regardless of body iron stores showed a lower rate. In addition to the rapid transport system, mucosal cells have a mechanism for putting iron into temporary storage. The transport and storage capacity appeared to regulate the amount absorbed into carcass until a critical dose of iron was given to normal and iron-loaded rats. When this dose was exceeded, a process suggestive of passive diffusion of iron was seen. The site studies confirm the duodenum as the most efficient site of iron absorption and emphasize the rather marked decrease in absorption found when the test dose of iron was injected only 4 to 6 cm distal to the pylorus. Extension into proximal jejunum of the more effective area for iron absorption was observed in iron-deficient animals.