Role of purified erythropoietin in the amplification of the erythroid compartment.

A single dose of Myleran induced a prolonged depletion of multi-potential haemopoietic cells and of early erythroid precursors to levels between 2 and 6 of control. In these mice, a priming dose of highly purified erythropoietin (Epo) or of any of 3 Epo preparations from different sources, and having different specific activities, increased the magnitude of the response to a test dose of Epo by erythropoietin responsive cells (ERC) in the hypertransfused mouse assay. As significant feeding into the ERC compartment from the most immature cells is unlikely because of the depletion induced by the Myleran, it may be concluded that highly purified Epo, not contaminated with other biologically active molecules, has a dual effect on the ERC: it causes increased amplification besides inducing differentiation into cells with the capacity to synthesize haemoglobin.