Low-Intensity Aerobic Exercise Mitigates Exercise-Induced Bronchoconstriction by Improving the Function of Adrenal Medullary Chromaffin Cells in Asthmatic Rats

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Exercise is one of the most common triggers of bronchoconstriction in patients with asthma. The low levels of circulating epinephrine produced by the adrenal medullary chromaffin cells (AMCCs) are associated with exercise-induced bronchoconstriction (EIB) in asthmatics. In the present study, we tested the hypothesis that low-intensity aerobic exercise may ameliorate EIB using a rat model of asthma. Male Sprague-Dawley rats at 7 weeks of age, sensitized with ovalbumin or treated with saline, were subjected to low or moderate exercise training (50 or 75% of maximum velocity) for one hour in a treadmill 30 min after ovalbumin or saline inhalation. The exercise capacity, airway responsiveness, lung morphology, the morphological changes and endocrine function of AMCCs were measured in both groups of rats after exercise training for 6 weeks. Either low-intensity or moderate-intensity exercise mitigated EIB and increased exercise capacity in ovalbumin-sensitized (asthmatic) rats. Low-intensity aerobic exercise reduced the vacuolar degeneration degrees, lipid contents, neuronal peripherin and neurofilament-68 expression, demolished neurites, but increased the chromaffin granule density, endocrine chromogranin A and phenylethanolamine N-methyltransferase expression in the adrenal medullary tissues, accompanied by increased levels of circulating epinephrine and corticosterone, but decreased nerve growth factor in asthmatic rats. Finally, low-intensity aerobic exercise significantly reduced the relative levels of phosphorylated extracellular signal-regulated kinase and phosphorylated cAMP responsive element-binding protein and the relative mRNA expression levels of downstream molecules, including c-FOS and c-JUN in the adrenal medullary of asthmatic rats. We suggest that low-intensity aerobic exercise improves the endocrine dysfunction of AMCCs and mitigates EIB.