Mitotic Activity in Vitro of Erythroblasts Previously Exposed to Erythropoietin

The proliferative activity of rabbit erythroblasts previously exposed to erythropoietin was studied in clot cultures containing colchicine. Erythroblasts exposed to erythropoietin in vivo (in the anemic animal) or in vitro (by shaking with anemic serum) showed high mitotic rates when subsequently cultured in an erythropoietin poor medium. These findings indicate that erythropoietin is taken up by erythroblasts from serum. Intracellular erythropoietin stimulates erythroblasts to increased mitotic activity. The direct effect of erythropoietin on the ability of erythroblasts to proliferate constitutes a mechanism by which erythropoietin regulates erythropoiesis.