Erythroid colony production in vitro as a function of exposure time to erythropoietin

The effects of timed exposure to erythropoietin of murine bone marrow cells has been studied in in vitro plasma clot cultures. Erythropoietin was added at the start of the incubation period, and at various times after initiation of the culture an anti-erythropoietin serum was added in an amount adequate to neutralize the erythropoietin. Culture methods were used which allow the transformation of the immediate progenitor stem cell of the recognized erythron, the CFU-E. The incorporation of 59Fe was used as an identity marker for hemoglobin synthesis which allowed the classification of colonies as erythroid in autoradiographs. Brief exposure to the hormone for one to two hours produced activation of about 20% of the control (continuous exposure for the 48 h of culture) value. More protracted exposure to erythropoietin caused the conversion of what appears to be a second population of CFU-E, but even 24 h of exposure was not adequate to cause the maximum activation of CFU-E seen in the control cultures.