Hematopoiesis in the rat: Quantitation of hematopoietic progenitors and the response to iron deficiency anemia

To determine the quantitative effects of iron deficiency on erythropoiesis and to assess the response of erythroid progenitors to sustained anemia, we developed quantitative assays for various hematopoietic progenitors in the adult, Sprague‐Dawley rat including erythroid colony‐ and burst‐forming cells (CFU‐E and BFU‐E), granulocyte/macrophage colony‐forming cells (CFU‐GM), and megakaryocytic colony‐forming cells (CFU‐Meg). CFU‐E were cultured in methylcellulose and grew best in the presence of fetal calf serum. CFU‐GM, BFU‐E, and CFU‐Meg grew better in normal rat plasma and required the presence of pokeweed mitogen‐stimulated rat spleen cell conditioned medium. The numbers of progenitors and nucleated erythroblasts in total marrow were estimated by the ratios of radioactivity in the humerus to the total skeleton as determined by radioiron dilution. The numbers of progenitors and erythroblasts in the spleen were measured by simple dilution. Sustained anemia was brought about through chronic iron deficiency. The response to iron deficiency anemia (IDA) was monitored by the numbers of the various progenitors and their cell cycle characteristics as measured by the tritiated thymidine suicide technique. With IDA, the number of CFU‐E in the body (marrow plus spleen) was increased to 3.5 times control, whereas the numbers of BFU‐E and CFU‐GM were unchanged. There was no difference in the percentage of CFU‐E, BFU‐E, and CFU‐GM in DNA synthesis (68%, 19.4%, and 18.8%, respectively). With iron therapy of IDA, CFU‐E numbers in marrow began to decrease by day 1 and fell in a manner reciprocal to changes in the hematocrit. Marrow and spleen erythroblasts, 1.7 times control in IDA, increased further to 3.9 times control by the fourth day after iron administration. There was no change in BFU‐E or CFU‐GM numbers in response to iron repletion, although the fraction of progenitors increased in the spleen. Thus, IDA does not limit the increase in CFU‐E seen with anemia, but does restrict erythroid maturation. Furthermore, the increase in CFU‐E and the state of chronic anemia occur without detectable changes in the number or cell cycle state of the more primitive BFU‐E.