RETICULOCYTE MEASUREMENTS AS A BIOASSAY FOR ERYTHROPOIETIN

The possibility of using reticulocyte counts in peripheral blood to as say erythropoietic activity of recombinant human erythropoietin (r-HuE PO) was evaluated in normal mice. Mice were injected subcutaneously wi th r-HuEPO on days 0, 1 and 2 and bled on day 4 for reticulocyte count determinations, using an automated counting system with thiazole oran ge fluorescent staining and flow cytometric analysis. Reticulocyte cou nts increased in a dose-dependent fashion upon administration of r-HuE PO. The reticulocyte count was unaffected by asialylated EPO as well a s other substances tested (interleukin-1, interleukin-3, dexamethasone , human chorionic gonadotropin). These data demonstrate the usefulness of employing reticulocyte counts as a rapid, specific and reproducibl e assay for in vivo erythropoietic activity of r-HuEPO.