Local Application of Atropine Attenuates the Upper Airway Reaction to Cold, Dry Air

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Abstract
In some individuals, inhalation of cold, dry air (CDA) provokes symptoms of rhinitis, accompanied by an increase in the levels of inflammatory mediators and markers of plasma leakage of recovered nasal lavages. Because rhinorrhea is a major component of this reaction and because nasal glands are heavily innervated by the parasympathetic system, we assessed the effect of atropine on the nasal reaction to CDA. Using a double-blind, randomized, crossover design, we administered a total dose of 0.5 mg of atropine or placebo intranasally to 18 volunteers before provocation with CDA. The reaction was monitored with symptom scores and by measuring the concentrations of histamine, N-alpha-p-tosyl-L-arginine methyl ester (TAME)-esterase activity and albumin, as well as the osmolality of lavage fluids before and after the provocation. Atropine significantly reduced rhinorrhea, the levels of histamine, and TAME-esterase activity as well as the osmolality of recovered lavage fluids, but had no effect on nasal congestion or albumin. Even with atropine, however, rhinorrhea and TAME-esterase activity were still significantly increased over the prechallenge baseline. Our results demonstrate that atropine-sensitive parasympathetic efferent pathways contribute to the CDA-induced rhinitis. We speculate that (1) the glandular and the vascular events of the upper airway reaction to dry air have different pathophysiologic mechanisms; (2) a significant component of TAME-esterase activity in lavage fluids may be of glandular origin; and (3) in addition to parasympathetic nerve activation, other mechanisms are involved in the upper airway reaction to dry air. The mechanism(s) leading to the reduction of histamine is unknown.