Role of the muscarinic M2 receptor in human nasal mucosa

Neurally mediated secretory hyperresponsiveness is a feature of allergic rhinitis (AR). Muscarinic M2 receptors are inhibitory autoreceptors which limit acetylcholine release at postganglionic parasympathetic nerve terminals, dysfunction of which has been implicated as a cause of bronchial hyperresponsiveness in asthma. The purpose of this study was to investigate the presence and function of M2 receptors in the human nose. In the first part of the study, nasal biopsies from subjects with AR (n = 12) and normal controls (n = 10) were examined for the presence of M2 receptor mRNA using polymerase chain reaction (PCR). In the second part, subjects with symptomatic AR (n = 17), with established contralateral secretory reflexes to bradykinin, underwent unilateral bradykinin challenge after premedication with pilocarpine, a M2 receptor agonist. The effect of pilocarpine on contralateral secretory reflexes was studied. M2 receptor mRNA was detected in 12 subjects (54%). Pilocarpine premedication led to a significant reduction of the contralateral secretory reflex to bradykinin. M2 receptors are present in the human nasal mucosa, though not universally. The function of M2 receptors in subjects with AR can be demonstrated using pilocarpine, however, more work is required to define their importance and potential role in nasal hyperresponsiveness