Reasons for performing study: Intense physical exercise can induce the degranulation of neutrophils leading to an increase in plasma concentration of the neutrophil marker enzymes myeloperoxidase (MPO) and elastase (ELT). These enzymes have pro-oxidative and pro-inflammatory properties and may play a role in the exercised-induced muscular damage.
Objectives: To measure MPO and ELT concentrations in plasma and muscles of endurance horses and to correlate them to the extent of exercise-induced muscular damage.
Methods: Seven endurance horses qualified on 120 km races were tested in this study. Neutrophil count, serum creatine kinase (CK), plasmatic and muscular MPO and ELT concentrations were measured before and 2 h after a 120 km endurance race.
Results: The race produced a significant increase of neutrophils, CK, and plasma MPO and ELT levels. A significant correlation was observed between the MPO and ELT values in plasma (r2= 0.92, P<0.01) and in muscles (r2= 0.89, P<0.01) while plasmatic concentrations of MPO and ELT were not significantly correlated to muscular ones. An increase of mean concentrations (± s.e.) of MPO (T0: 9.85 ± 3.9, T1: 228.9 ± 95.9 ng/mg proteins) and ELT (T0: 8.4 ± 2.4, T1: 74.5 ± 39.7 ng/mg proteins) in the muscles were observed after the race. Interestingly, the individual data showed large differences between the horses. Muscular MPO and ELT concentrations were significantly correlated to plasma CK levels. The coefficient of correlation (r2) was 0.69 (P<0.01) for MPO and 0.66 (P<0.01) for ELT, respectively.
Conclusions: Results underline the possible role of MPO and ELT in exercise-induced muscular damage.
Potential relevance: Further studies should investigate the effect of exercise type and intensity, as well as the role of the training state on MPO and ELT involvement in muscular damage. The assessment of the intensity of exercise-induced neutrophilic degranulation may have a potential role in the monitoring of the athletic career.