Immunoreactive erythropoietin and erythropoiesis stimulating factor(s) in plasma from hyper-transfused neonatal and adult mice. Studies with a radioimmunoassay and a cell culture assay for erythropoietin

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Abstract
The objective was to study whether the high erythropoietic stimulatory activity found in plasma from neonatal mice during the growth period in erythropoietin (Ep) alone, or Ep in combination with other factors. Plasma from hypertransfused neonatal (20 d) and adult (13-20 weeks) mice were compared with a radioimmunoassay (RIA) and a cell culture assay for Ep. The RIA determines immunoractive Ep (iEp) while the cell culture assay reflects erythropoiesis stimulating factor(s) (ESF). Compared to control values, hypertransfusion resulting in PCVs of 55% and higher reduced the mean iEp levels in neonatal and adult mice by 82% and 38%, respectively (P < 0.01). There was no detectable difference between the mean iEp levels of hypertransfused neonatal and adult animals (P > 0.3). The parallel ESF data showed a reduction in mean plasma ESF levels by 68% in hypertransfused neonatal and 72% in hypertransfused adult animals (P < 0.001). And notably, in contrast to the iEp data, the mean ESF level found in hypertransfused neonatal mice with PCVs of 55% and higher was significantly above that of hypertransfused adult animals (P < 0.001). No correlation was found between PCV anbd iEp (r < 0.4, P > 0.1) or ESF (r < 0.2, P > 0.2) in hypertransfused animals. The parallel data from the wo Ep assays show that plasma from hypertransfused 20-d-old mice contain one or more erythropoietic stimulatory factors not detected by the RIA. It is concluded that part of the high erythropoietic stimulatory activity found in plasma from neonatal mice is due to non-Ep factors.