The Role of the Intestine in Iron Kinetics

Abstract

Following a parenteral dose of iron59 radioautographs of the small intestine showed radioactivity concentrated within the mucosal cells. Quantitative studies demonstrated maximal concentration of radioiron in the small intestine 16 to 24 hours after intravenous injection with a subsequent decline in radioactivity to baseline levels during the life span of the small intestinal epithelial cells. To test the hypothesis that the mucosal content of iron influences the quantity absorbed, absorption of oral iron59 was measured at periodic intervals after the intravenous injection of cold iron. Absorption was least at the time the parenteral dose was maximally concentrated within the intestinal epithelium. Injected iron exerted less effect upon absorption during the period it was circulating in the plasma or fixed in body stores. Further, serial decreases in absorption of an oral dose of iron59 were observed following graduated increases in the parenteral dose of iron. The relationship between the intestinal iron content and quantity of iron led us to believe that the iron content of intestinal epithelium acted to regulate absorption. Previous investigators have doubted this hypothesis because increased absorption has been shown in certain conditions with increased iron stores. This paradox can be explained by demonstration that body stores are not always in constant equilibrium with the iron content of intestinal mucosal cells. Further, since the amount of body iron deposited in intestinal cells varies with body requirements and mucosal cells are sloughed from this villus into the lumen of the gut, iron is lost in a selective manner so that needed iron is conserved and excess eliminated.