Changes in the susceptibility of red blood cells to oxidative and osmotic stress following submaximal exercise.

Red blood cell (RBC) susceptibility to oxidative and osmotic stress in vitro was investigated in cells from trained and untrained men before and after submaximal exercise. Whilst no significant change in peroxidative haemolysis occurred immediately after 1 h of cycling at 60% of maximal aerobic capacity (VO2max), a 20% increase was found 6h later in both groups (P < 0.05). The RBC osmotic fragility decreased by 15% immediately after exercise (P < 0.001) and this was maintained for 6h (P < 0.001). There was an associated decrease in mean cell volume (P < 0.05). Training decreased RBC susceptibility to peroxidative haemolysis (P < 0.025) but it did not influence any other parameter. These exercise-induced changes were smaller in magnitude but qualitatively similar to those found in haemopathological states involving haem-iron incorporation into membrane lipids and the short-circuiting of antioxidant protection. To explore this similarity, a more strenuous and mechanically stressful exercise test was used. Running at 75% VO2max for 45 min reduced the induction time of O2 uptake (peroxidation), consistent with reduced antioxidation capacity, and increased the maximal rate of O2 uptake in RBC challenged with cumene hydroperoxide (P < 0.001). The proportion of high-density RBC increased by 10% immediately after running (P < 0.001) but no change in membrane-incorporated haem-iron occurred. In contrast, treatment of RBC with oxidants (20-50 mumol.l-1) in vitro increased cell density and membrane incorporation of haem-iron substantially. These results showed that single episodes of submaximal exercise caused significant changes in RBC susceptibility to oxidative and osmotic stress. Such responses may account for the increase in RBC turnover found in athletes undertaking strenuous endurance training.