Evaluation of the erythroid regenerative response in two different models of experimentally induced iron deficiency anemia

Anemia was induced in weanling Sprague Dawley rats either by feeding an iron-deficient diet or by chronic phlebotomy. The erythroid regenerative response was then evaluated before and after a hemolytic event, and results were compared with those of a third group of control nonphlebotomized rats fed an iron-replete diet. Diet and phlebotomy groups developed a similar degree of anemia (mean hemoglobin concentration 7.9 g/dL and 7.8 g/dL, respectively; controls, 13.9 g/dL) and hypoferremia (mean serum iron concentration 25.4 mug/dL and 34.9 mug/dL, respectively; controls, 222.0 mug/dL). However, the anemia in diet rats was nonregenerative (reticulocyte count, 83.1x10(3) cells/muL) and associated with bone marrow erythroid hypoplasia; whereas the anemia in phlebotomy rats was regenerative (reticulocyte count, 169.6x10(3) cells/muL) and associated with bone marrow erythroid hyperplasia. Thrombocytosis was seen in diet rats (1,580x10(3) cells/muL) but not phlebotomy rats (901x10(3) cells/muL) when compared with controls (809x10(3) cells/muL). To further evaluate the regenerative capability phenylhydrazine (PHZ) was administered to induce hemolysis. Erythrocyte mass declined approximately 25% in all groups, including controls. The reticulocytosis (265.3x10(3) cells/muL) seen in phlebotomy rats was earlier and significantly greater than that seen in either diet or control rats. Hemoglobin concentration returned to pre-PHZ concentrations (7.9 g/dL) in phlebotomy rats within 4 days posthemolysis. In diet rats, the maximal regenerative response (176.3x10(3) cells/muL) was not seen until 8 days posthemolysis, and hemoglobin (7.5 g/dL) did not return to pre-PHZ concentrations during the 8-day study. In many aspects, the anemia seen following diet- or phlebotomy-induced iron deficiency was similar. However, the erythroid regenerative capability varied depending on the mechanism by which anemia was induced and furthermore altered the efficiency of hemoglobin production following a hemolytic event. These results suggest that the availability of iron in the diet may modulate the pathogenesis of iron deficiency anemia. (C) 2001 American Society for Veterinary Clinical Pathology.