Erythropoietin bioassays using fetal mouse liver cells: validations and technical improvements

Studies are described which were designed to compare an erythropoietin (Ep) bioassay using the uptake of 125I-deoxyuridine (125-I-UdR) into whole cells cultured in micro-titer plates with an established method where the cells were cultured in 1 ml volumes using the incorporation of 59Fe into heme as the endpoint. The results demonstrate the validity of the substitution of 125I-UdR uptake into whole cells as a replacement for 59Fe incorporation into heme as an assay endpoint and the adaptation of the method to a semi-micro scale with automated cell harvesting. A culture time significantly shorter than 24 h is demonstrated not to be of practical benefit. Two methods are proposed to saturate the growth promoting effects of iron-containing transferrin. The performance of semi-micro, serum-containing bioassay employing untreated serum as the test material is shown to be superior to previous systems for the biological measurement of Ep.