Background: Eosinophils contain granule proteins such as eosinophil cationic protein (ECP) that have proinflammatory effects on airways. ECP may be released on activation of eosinophils into the plasma and is widely used as a marker of bronchial hyperreactivity and allergic inflammation. Environmental factors as well as intense physical exertion may influence eosinophil-related bronchial hyperreactivity.
Study objectives: To investigate the effect of endurance exercise at moderate altitude on levels of circulating eosinophils, serum ECP, serum osmolality (sOS), and dynamic pulmonary function parameters in healthy mountaineers.
Setting: Alpine field study performed in the Alps of Upper Styria in Austria.
Type of exercise: Ascent of a mountain at maximal speed.
Participants: Thirty healthy male volunteers from a troop of military mountaineers.
Results: Mean ECP concentration increased by 66% at the summit checkpoint (H2) and remained at 63% above baseline (base checkpoint [H0]) after descent (H4), while the blood eosinophil count decreased concomitantly from 250/μL at H0 (preexercise) to 118/μL (53%) at H2 and to 22/μL (81%) at H4. The total serum ECP concentration adjusted to sOS correlated negatively with blood eosinophil count (r = − 0.37; p < 0.0001) and Pao2 (r = − 0.34; p < 0.001), but positively with the peak expiratory flow (PEF) [r = 0.45; p < 0.0001]. Although sOS correlated with serum ECP at H2 (r = 0.47; p = 0.02) and at 12 h after the start of the experiment (H12) [r = 0.57; p = 0.003], the relationship between total ECP and sOS (r = 0.19; p = 0.034) was less pronounced. FEV1 in percentage of FVC (%FEV1/FVC) [the Tiffenau test], forced expiratory flow rate at 25% of vital capacity, and PEF were significantly higher at H2 than at H0 and H4. %FEV1/FVC decreased to 88% (p < 0.01) and 83% (p < 0.001) predicted at H12 and 24 h after start of the experiment, respectively.
Conclusion: Results provide strong evidence for nonspecific activation of blood eosinophils during prolonged intense aerobic exercise at moderate altitude, modifying both eosinophil dynamics and regulation of ECP release in healthy subjects.