Simultaneous effects of erythropoietin and colony-stimulating factor on bone marrow cells.

Erythropoietin or colony-stimulating factor, or both, were added to rat or mouse marrow cell cultures, and the responses to each inducer were measured. Colony-stimulating factor caused the suppression of erythropoietin-stimulated hemoglobin synthesis, and erythropoietin caused the suppression of the granulocyte-macrophage colony formation that is dependent on colony-stimulating factor. The extent of suppression by each inducer was dose-dependent. Marrow cells from plethoric rats were more sensitive to suppression of erythropoietin action by colony-stimulating factor than were normal marrow cells. These findings suggest that either (i) the receptors for erythropoietin and for colony-stimulating factor have overlapping specificities and that the "wrong" inducer may bind without having an inductive effect, or (ii) the target cells for erythropoietin and colony-stimulating factor are very closely related or are the same.