In vitro assay of erythropoietin in fetal mouse liver cultures. II. Effects of human transferrin bound iron and of serum on the stimulation of incorporation of 3H-thymidine into DNA.

: Iron bound to human transferrin but not apotransferrin, increases the effect of erythropoietin in stimulating incorporation of 3H-thymidine into DNA in fetal mouse liver cells in vitro. The effect of erythropoietin, with or without transferrin-iron is blocked by pre-incubation of the erythropoietin with rabbit anti erythropoietin serum. Human sera contain factors in addition to erythropoietin and transferin-iron which may modify the stimulation of incorporation of 3H-thymidine into fetal mouse liver DNA induced by erythropoietin. Heat treatment of sera at 56 degrees C for 30 min does not necessarily destroy these factors. Acid heat treatment of sera (pH 5.5 and 100 degrees C for 5 min) may destroy inhibitory factors and can result in an apparent increase in serum erythropoietin activity assessed in this fetal mouse liver system.