In Vitro Effect of Erythropoietin on the Spleen of the Polycythemic Mouse. III: Limited Exposure to Erythropietin and Actinomycin D

1. Heme synthesis and appearance of erythroblasts were observed when the spleen fragments from the polycythemic mouse spleen were exposed to erythropoietin only in the earlier period of incubation. The heme synthesis and the number of erythroblasts were increased in proportion to the exposure time to erythropoietin up to 12 hours. Twelve hours exposure to erythropoietin evoked about 70 percent of the maximally stimulated control heme synthesis.

2. The appearance of erythroblasts and the heme synthesis was completely blocked by the addition of 0.01 µg./ml. of actinomycin D. Some population of differentiated erythroblasts became resistant to actinomycin D which was added at 12th and 24th hour of incubation.

3. The heme synthesis within reticulocytes from bled anemic mice were not affected by these doses of erythropoietin, actinomycin D or both of them.

4. The results were discussed in connection with the mechanism of erythropoietin on stem cells.