Chronic experimental iron losses in rats not leading to overt iron deficiency: a model for the regulation of the whole-body iron balance in an iron-replete condition.

Intestinal iron absorption studies, which include investigation of iron deficiency, increased erythropoiesis, low iron diet and acute bleeding, have been done, but none have reported the regulation of the balance of an iron-replete individual. We bled rats at regular time intervals, such that the experimentally induced iron losses were compensated by iron from storage and nutritional procurement without the onset of anemia. During these experimental periods the hemoglobin and plasma iron concentrations were determined along with repeated histochemical gradings of the bone marrow iron. We determined the intestinal iron absorption at regular intervals after having established its relation to the intragastric ferrous iron dose. The results obtained show that regular bleedings of 15-20% of the total blood volume every 10 days or twice a week, respectively, are compensated completely by storage and nutritional iron procurement without the onset of anemia. The intestinal iron absorption is increased 4 hours after an acute bleeding and was found high during the period that the animals were bled every 10 days. Significant changes of the plasma iron concentration, mostly within the "normal range" are invariably associated with experimental changes in bleeding regimes. The observed increases of the intestinal absorption of a ferrous iron test dose and decreases of the plasma iron concentrations that precede the depletion of the histochemically graded bone marrow iron are interpreted by a modification of a reported model, in which the process of iron release into the plasma from the reticuloendothelial system and the gut mucosa is linked closely to the actual plasma iron concentration.