In vivo evidence for the functional heterogeneity of transferrin-bound iron. III. Studies of transferrin at high and low iron saturation.

The functional heterogeneity of the transferrin iron pool of rats was studied by means of selective radioiron labeling of transferrin at high and low iron saturations. A sample of iron-poor plasma transferrin brought to 90 per cent iron saturation by the addition of 59Fe-nitrilotriacetate was mixed with a similarly labeled plasma sample of 55Fe-transferrin at 10 per cent iron saturation. The mixture was injected intravenously into groups of normal rats which were killed after 30 minutes, 3, and 24 hours for measurement of the distribution of the 59Fe and 55Fe in various tissues. 59Fe from diferric transferrin disappeared more rapidly from plasma and was preferentially removed by red blood cells, bone marrow, liver, and spleen. This phenomenon was most apparent at 30 minutes and 3 hours with little difference in the distribution of 59Fe and 55Fe at 24 hours. These studies add further support for the Fletcher-Huehns hypothesis of the functional heterogeneity of the transferrin iron pool in the rat.