The biological effects formerly attributed to erythropoietin were generally observed using impure preparations of the hormone containing, among the impurities, bacterial endotoxin, a contaminant that has recently been shown to affect the haemopoietic system. Erythropoietin, purified to apparent homogeneity and freed of trace contamination by endotoxin (1) promotes erythroid burst formation from mouse marrow cells in semi-solid culture medium, (2) stimulates haemoglobin synthesis in rat marrow cell cultures, (3) stimulates transcription in mouse and rat bone marrow cell cultures and (4) causes the formation of the cytoplasmic mediator protein in rat marrow cells, which enhances transcription in isolated nuclei.
