In vitro assay of erythropoietin in fetal mouse liver cultures. I. Comparison of radioactive tracers and evidence of assay specificity.

In a 13 d fetal mouse liver tissue culture system for assay of erythropoietin, stimulation of incorporation of 3H-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 1300 IU, 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 hormones on both DNA and haem synthesis.