Abstract
The aerobic metabolic rate may increase up to 10-fold during physical exercise, enhancing leakage of oxygen radicals from the mitochondria to the cytosol. This rise in oxygen free radical concentration could exceed the protective capacity of cell antioxidant defence systems and cause oxidative changes of lipid membranes and membrane skeletons. Structural changes in red blood cell (RBC) membrane skeletons have been observed with scanning electron microscopy after a marathon race. Endurance exercise has also been shown to increase Malondialdehyd (MDA) concentration, a breakdown product of oxidative damaged polyunsaturated membrane lipids. After endurance exercise RBC´s show decreased osmotic resistances and are more susceptible to mechanical stress. We tested the hypothesis, that hemolysis in endurance exercise is associated with structural changes of RBC membrane skeletons and lipids and investigated the effect of workload intensity even in frequently performed types of endurance training
Ten healthy, endurance trained male triathletes were subjected to two 35 min constant workloads at moderate and heavy bicycle ergometry. Immediately before and after ergometry blood samples were collected from antecubital vein. Plasma haptoglobulin (HP) concentration was measured by a radial immunodiffusion assay as an indicator of hemolysis. Malondialdehyd (MDA) concentration was measured by a flurescencephotometric method using thiobarbituric acid as reactant and tetraethioxypropan as a standard. For detection of erythrocyte membrane proteins the erythrocyte were washed and hemolyzed, membrane proteins were sedimented by centrifugation, denaturated and subjected to horizontal SDS polyacrylamide gel electrophoresis. The protein pattern obtained in the gels was visualised by silverstaining. Every 2.5 minute during ergometry venous capillary blood samples were collected from the earlobe. This samples were used to measure lactate concentration by a enzymatic method using laktatdehydrogenase.
Moderate bicycle ergometry (58.7 ± 4.5 % of VO2peak) : Lactate concentration increase during erometry was below 1 mmol/l indicating a steady state. No significant changes were observed in MDA and HP concentration. MDA concentration did not correlate with Lactate concentration. Membrane proteins exhibited the normal patterns.
Heavy bicycle ergometry (73.3 ± 8.9 % of VO2peak) : Mean Lactate concentration increase was 3.3 ± 1.0 mmol/l indicating a intensity above the steady state. MDA concentration increased (p < 0.05) by 5.7 ± 6.5 %. MDA concentration correlated with Lactate concentration. HP decreased (p < 0.05) by 16.0 ± 10.6 %. Preexercice membrane proteins exhibited the normal gel electrophoresis patterns, postexercice membrane proteins showed in 50 % of the gels distinctly diminished Spectrin bands.
After moderate bicycle ergometry the measured indicators for oxidative red cell membrane alterations showed no significant changes. After heavy bicycle ergometry the haptglobolin concentration decreased, indicating a hemolysis during exercise. The MDA concentration increased and correlated with the break-off lactate, indicating peroxidation of polyunsaturated lipids and suggests a connection with increasing exercise intensity. The diminished Spectrin bands in the postexercise gels could be due protein oxidation and enhanced susceptibility to proteoytic degradation following oxidative denaturation. The observed diminishment of the spectrin - bands could be due to proteolytic modification ex vivo. Thus, the hemolysis in heavy bicycle ergometry may be related to increased chemical and physical susceptibility following oxidative alterations in RBC membrane lipids and membrane.
Thus, 35 minute intensive endurance training seems to be a physiological stress sufficient for alterations of lipids and proteins of the RBC membrane. The latter changes may be related to increased susceptibility to chemical and physical stress and may contribute to hemolysis in endurance exercise. |
