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Erythropoietin‐induced rheological changes of rat erythrocytes

The effects of recombinant human erythropoietin (rhEPO) on red blood cell (RBC) rheological properties were investigated in rats. Rats received intramuscular injections of 150 U/kg/d rhEPO for 5 d, following which blood samples were obtained 1, 5 or 10 d later. RBC deformability was assessed by determining cell transit times through 5‐µm micropores (CTA) and RBC shape recovery time constants via photometry, aggregation in plasma and dextran was measured by photometry and RBC electrophoretic mobility was determined in a cylindrical electrophoresis system. RBC aggregation was found to be significantly decreased on day 5 after rhEPO treatment (P < 0·05), yet was unchanged from control on days 1 and 10. Mean RBC micropore transit times remained unchanged, but the distributions of transit times were altered; compared with control, the 5th percentiles on both days 1 and 5 were decreased and the 95th percentile on day 1 was elevated. Electrophoretic mobility of RBCs in phosphate‐buffered saline was significantly increased on day 5 after rhEPO treatment (P < 0·05), with mobility measurements in dextran 500 (MW = 500 kDa) solutions suggesting that the cells' surface properties related to the formation of a ‘depletion layer’ may be altered on day 1. These results indicate that the rheological behaviour of RBC as a consequence of rhEPO treatment are temporal and are affected by the presence of reticulocytes as well as by the average age of the circulating cells.