The interaction of erythropoietin with fetal liver cells. I. Measurement of proliferation by tritiated thymidine incorporation.

Erythropoietin stimulates the erythropoietin responsive cell to undergo DNA synthesis and subsequent mitosis. To define further the physiology of this effect, a liquid suspension microculture utilizing mouse fetal liver cells was developed. Tritiated thymidine incorporation into erythroid precursors was found to parallel radiolabeled iron incorporation with peak DNA synthesis occurring after 24 hours of culture. Both tritiated thymidine and iron incorporation were dependent on erythropoietin concentration. The responsiveness to erythropoietin decreased when erythropoietin was withheld and this diminishment in reactivity paralleled a morphological differentiation of the cells. This observation, together with the finding that erythropoietin activity could be removed by absorption with large numbers of cells, suggests the proliferation induced by erythropoietin depends on a specific stage in the differentiation of the red blood cell and may be mediated through a specific cellular receptor.