Erythropoietin production in normoxic and hypoxic rats with increased blood O 2 affinity

Abstract

Effects of an acute increase in blood O 2 affinity on erythropoietin production were studied in normoxic and hypoxic male rats. Blood O 2 affinity was increased by exchange-transfusion with blood from sodium cyanate rats. P 50 was lowered to 27.6 torr (pH 7.4, P CO 2 = 40 Torr, 37°C) in the recipients compared to 41.8 torr in control rats exchange transfused with normal blood. Hypoxia was induced by exposure to simulated high altitude (4750 or 7000 m) for 16 h. Erythropoietin was determined by in vivo bioassay. In rats with normal blood O 2 affinity, plasma erythropoietin was undetectable at 300 m, 0.26 ± 0.10 U/ml at 4750 m (mean ± SEM; n = 7)_, and 3.52 ± 0.58 U/ml at 7000 m (n = 10)). Plasma erythropoietin titers were significantly ehanced in rats with high blood O 2 affinity at 300 m 0.05 ± 0.01 U/ml; n = 4) and moderately increased at 4750 m (0.57 ± 0.12 U/ml; n = 7), but unchanged at 7000 m (3.88 ± 0.74 U/ml; n = 10). These results indicate that a high blood O 2 affinity reduces the O 2 delivery to the cells controlling eryhtropoietin production in normaxia and moderate hypoxia. However, this is offset at serve hypoxia most likely by an improved O 2 loading to the blood.