Iron excretion in iron-overloaded rats following the change from an iron-loaded to an iron-deficient diet

Background: Iron stores in the body are thought to be regulated by a mechan ism associated with the rate of iron absorption from the diet, with no sign ificant role played by iron excretion. We report the existence of an iron e xcretory process that results in the loss of significant amounts of liver i ron. Methods and Results: Rats were fed 3% carbonyl iron for 9 weeks, which resu lted in a 20-fold increase in liver non-haem iron. When the rats on this ir on-loaded diet were switched to a low iron diet for 2 and 7 days, liver non -haem iron levels fell 30% and 45%, respectively. A similar fall in transfe rrin-bound plasma iron was also seen. As the liver iron had not redistribut ed to other body compartments, it was concluded that the iron had been excr eted and that the excreted iron represented a loss of 22% and 28% in total body non-haem iron over 2 and 7 days, respectively. Ligation of the common bile duct in iron loaded rats that had been switched to the iron-deficient diet was accompanied by a similar loss of liver iron and also hepatocellula r damage. In addition, measurement of enterocyte iron levels showed that on ly approximately 5% of the total iron excreted was found in these cells. Conclusion: Neither bile nor enterocytes play a significant role in iron ex cretion. The similarity in the degree of fall in transferrin-bound iron lev els with a change in diet suggests that iron excretion involves the uptake and excretion of transferrin bound-iron, possibly by goblet cells. The obse rved hypertrophy of the intestinal mucosa associated with carbonyl iron fee ding may facilitate hypersecretion of mucous and the excretion of this iron . (C) 2000 Blackwell Science Asia Pty Ltd.