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The present study was performed to observe alterations in myeloperoxidase (MPO)-activity in serum samples obtained from exercised Standardbred trotters under field conditions. Results were compared with parameters for oxidative damages to proteins and lipids as well as with the increase in cellular enzymes as marker of general tissue damage.
For this reason, 5 blood samples from 20 healthy Standardbred trotters were taken prior and following (5 minutes, 4 hours, 24 hours and 48 hours) a regular training exercise, normally performed twice a week.
The alterations in serum enzymes creatine kinase, aspartate aminotransferase, lactate dehydrogenase and lactate were measured. In addition, red and white blood cell counts and differentials were determined to observe changes in the subpopulations of neutrophil granulocytes. As parameter for oxidative damage, malondialdehyde (MDA) and carbonylated proteins were determined. To assess exercise intensity, we recorded continuously heart rate, speed, as well as duration and covered distance for each of the 20 horses.
Exercise resulted in a significant increase in MPO-activity from a median value of 0.48 U/l (mean of 0.56 ± 0.41 U/ml) to 2.17 U/l (mean 2.42 ± 1.22 U/ml). Four hours after termination of training, MPO-activity was only about 50 % above resting values. After 24 and 48 hours MPO-activity was under pre-exercise level.
The exercise induced increase of carbonylated proteins was slight and not significant. Mean MDA-concentration in serum was significantly increased after exercise, showing oxidative damage in lipids. A positive correlation was seen between erythrocyte count and MDA at rest and after 48 hours. Alterations in leukocyte and erythrocyte numbers were significant after exercise, as were those of lactate and serum enzymes, indicating tissue damage, but no correlation with MPO-activity. However, MDA showed highest values at the same time as MPO-activity. Increase of juvenile neutrophils was also significant after 48 hours, indicating an activated cellular immune system. Results demonstrate that regular training exercise leads to considerable alterations in MPO activity in serum of healthy trotters as a result for cellular immunologic reactions as well. Simultaneously, exercise induced oxidative stress occurred in lipids.
We found a considerable reaction of the cellular immune system by changes of MPO, increase in total neutrophils and subsequent rise of juvenile neutrophils.
For further studies it would be of special interest, to observe alterations in MPO-activity in smaller time intervals after exercise as well as comparisons between MPO-activity and concentration.