In Vitro Assay of Erythropoietin in Fetal Mouse Liver Cultures

S ummary . In a 13 d fetal mouse liver tissue culture system for assay of erythropoietin, stimulation of incorporation of H-thymidine and of ¹²⁵I-iodo-2'-deoxy uridine into DNA and of ⁵⁹Fe iron into haem were compared as metameters of erythropoietin effect. With both DNA and haem tracers, log-dose response curves given by two preparations of human urinary erythopoietin purified to different extents (respectively 2 and 1300IU, by bioassay in vivo , per mg of protein) were essentially identical at low dose levels although at high dose levels the less pure preparation decreased stimulation of both DNA and haem synthesis. Pre-incubation of erythropoietin with an antiserum to human erythropoietin abolished the effects of the hormone on both DNA and haem synthesis.