Abstract
A new method of quantitative ^14^C‐autoradiography was applied for evaluating possible effects of erythropoietin (ESF) on the DNA synthesis rate of differentiated erythroid murine bone marrow cells identified as proerythroblasts, basophilic and polychromatic erythroblasts. Eosinophilic myelocytes were used as a control cell population. ESF was prepared from the urine of a patient with chronic aplastic anemia; an inactive urinary preparation served as control. The potency of the preparations was estimated by the ^59^Fe‐incorporation assay. The materials to be tested were injected into polycythemic mice 4, 8 and 16 hours before in vitro short‐term incubation of the bone marrow cells with ^14^C‐thymidine and Methotrexate. Animals without test material were taken as additional controls. Autoradiographic grains were counted by an incident light microscope photometer.
Eight hours after injection of ESF a significant increase in the mean ^14^C‐thymidine incorporation was found in all three erythroid cell types when compared either with the inactive control preparation (excess incorporation 30–40%) or with the untreated control animals (excess incorporation 10–20%). It could be shown that the increase is due to an immediate action of ESF on already differentiated cells and cannot –‐ at least not solely –‐ be attributed to its action on hemopoietic stem cells. The control preparation which was inactive in terms of ^59^Fe incorporation exerted a slight inhibition of DNA synthesis rate in all erythroid cells as well as in cells not committed to erythroid differentiation.