Intestinal Absorption of Hemoglobin Iron

Abstract

The enhanced absorption of hemoglobin iron in iron deficiency was studied in iron-deficient and iron-loaded rats. Both groups were given 59Fe-labeled hemoglobin by gastric intubation and the radioactivity of each rat was measured in a whole body counter at 3 hr and at 9 days. In addition, 59Fe-labeled hemoglobin was instilled into closed duodenal loops of iron-deficient and iron-loaded rats. Three hours later radioactivity was measured in the duodenal washings and in the carcass and duodenum separately using a whole body counter. Radioactivity of hemoglobin and of heme in the washings were measured after separation by charcoal adsorption. Heme and radioiron split from heme were measured separately in homogenates of duodenum using a nonheme iron extraction method. The results indicated that: (1) iron-deficient rats absorb up to 20 times more iron from hemoglobin than do iron-loaded rats; (2) deferioxamine did not influence absorption of hemoglobin iron, indicating that iron split from hemoglobin intraluminally does not contribute significantly to absorption; (3) during the 3-hr closed loop study intraluminal splitting of heme from hemoglobin was the same in both groups, 2 times more heme entered iron deficient mucosa compared with the iron loaded, and, most importantly, 3 times as much iron was transported to carcass by iron deficient mucosa; (4) little, if any, heme was transported as such to the carcass. These results suggest a mucosal mechanism for absorption of hemoglobin iron as well as ionic iron and that the mechanism is enhanced in iron deficiency. The final step in absorption of hemoglobin iron, namely the transport of Fe++ from mucosal cell to plasma, may be rate limiting as it is for absorption of elemental iron. This suggests a common site for regulation of absorption of both elemental and hemoglobin iron.