 mechan erythropoietin-induc differenti iv characterist erythropoietin action hemoglobin synthesi marrow cell cultur characterist erythropoietin stimul hemo- globin synthesi rat marrow cell cultur studi relationship cell number rate hemoglobin synthesi va- riou level erythropoietin sigmoid linear suggest cooper action sensit cell magnitud erythropoietin cell increas time contact hormon time on-half maxim discer- nibl loss erythropoietin cultur medium de- cribe lag time respons erythropoietin appear condit cultur disappear cell pre-- incub 9 replac larg fraction medium 24-h interv enabl cell continu hemoglobin synthesi addit 24 