The Gastrointestinal Tract and Iron Absorption.

IT HAS BEEN demonstrated repeatedly that intestinal absorption of iron is responsive to the body’s needs; enhanced absorption being found with increased need,’-5 and diminished absorption with decreased need.”5’6 Thus there is agreement that intestinal iron absorption is regulated, but there is no general agreement as to the nature of the regulatory mechanism. As part of all previous hypotheses on the mechanism of control, two assumptions had been held:912 (1) The amount of iron which entered the intestinal epithelial cells was believed to participate in the control of subsequent iron absorption. (2) All iron entering intestinal epithelial cells was absorbed into l)lood. Studies reported by Conrad et al.1’ suggested that the second assumption was not valid. These studies were done by giving Fe59 intragastrically to rats which were later killed at varying intervals. Four hours after the animals were dosed, radio-autographs of the small intestine showed the entire villus to be labeled, and over the next 24 hours, progression of babel toward villous tip was seen. These investigators postulated that iron held in this way by epithehal mucosal cells might subsequently be absorbed into blood or, as movement of the label indicated, might be sloughed into the lumen with the epithelial cell at the end of its life span. No data were presented regarding how much iron this might represent or if it constituted a significant proportion of iron entering intestinal epithelial cells. If it did, another concept of iron absorption had to be considered, i.e., unregulated entry of iron into intestinal epithelial cells with the controlling mechanism regulating only subsequent movement from epithehial cells to blood. The present report attempts to add further information along these lines.