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EXERCISE-INDUCED ASTHMA MAY BE ASSOCIATED WITH DIMINISHED SWEAT SECRETION RATES IN HUMANS

¹Departments of Emergency Medicine and ²Division of Pulmonary and Critical Care Medicine and ³Department of Clinical Investigation, Naval Medical Center, San Diego ⁴Department of Medicine, the University of California, San Diego, CA; and ⁵Department of Physiology, University of Michigan Medical School, Ann Arbor, MI

ridiculo{at}umich.edu

Abstract

BackgroundMuscarinic receptor agonists increase water secretion from the acinar cells of respiratory, sweat, salivary, and lacrimal glands. Mice lacking the gene for the aqueous water channel aquaporin-5 exhibit methacholine-induced bronchiolar hyperactivity when compared to normal mice. Individuals with asthma also have enhanced airway responsiveness to methacholine and diminished airway hydration. Because aquaporin-5 in humans is also expressed in respiratory, sweat, salivary, and lacrimal glands, we hypothesized that those individuals with exercise-induced asthma and excessive bronchiolar reactivity should also have decreased muscarinic receptor-dependent sweat, salivary, and tear gland secretion. Methods: Healthy, athletic subjects suspected of having exercise-induced bronchospasm were recruited, and forced expiratory volumes (FEV₁) were determined following provocative airway challenges with methacholine. Measurements of pilocarpine-induced sweat secretion were taken in 56 volunteers, and some additional subjects also had timed collections of oral secretions and lacrimal tearing. Results: Subjects manifesting excessive airway reactivity demonstrated by exaggerated methacholine-induced reductions in FEV₁ also had diminished values for pilocarpine-induced sweat secretion (n = 56, r = -0.59, p < 0.0001). The rate of pilocarpine-stimulated sweat secretion in our subjects correlated highly with salivary flow (r = 0.69, p < 0.0001) and tearing (r = 0.86, p < 0.001) rates. Conclusion: Hyperhidrosis, sialorrhea, and excessive tearing are traits that may indicate a phenotype that predicts resistance to hyperactive airway diseases such as exercise-induced asthma in humans.

Key wordsExercise-induced asthma, Sweat, Salivary gland, Aquaporin, Tearing, Humans