Radioimmunoassay of haemoglobin F in K 562 cells following induction with renin substrate and erythropoietin.

To test the hypothesis of renin substrate (RS; angiotensinogen) being a precursor of erythropoietin (EP), the capacity of RS and EP to induce Hb synthesis was compared in cultured human erythroid leukaemia cells of the K 562 line after prestimulation with haemin. For this purpose a radioimmunoassay for haemoglobin F (HbF) was developed. This assay was shown to be specific for HbF, reproducible, and sensitive for 0.1 ng of HbF. The cells were induced by RS and EP to increased HbF production. Cells stimulated with RS or EP showed increased benzidine staining. This data, corroborating our earlier observations on immunological similarities between RS and EP, supports the hypothesis that renin substrate is a likely precursor of erythropoietin.