Localization and function of histamine H3 receptors in the nasal mucosa

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By RT-PCR, histamine H3 receptor mRNA was not expressed in the nasal mucosa in the inferior turbinate of allergic rhinitis patients. In order to clarify the localization of histamine H3 receptors in the nasal mucosa, immunohistochemical study was performed using a monoclonal antibody against histamine H3 receptor in the inferior turbinate of allergic rhinitis patients. Positive signals were observed around submucosal glands. The localization of the positive signals on the periphery of the gland suggests two possibilities. First, H3 receptors may be on the basolateral membranes of gland cells. Second, H3 receptors may be on the presynaptic region of the nerves innervating these glands cells. Absence of H3 receptor mRNA in the nasal tissues supports the latter possibility. The above results suggest a possible involvement of histamine H3 receptors in mucus secretion of submucosal gland. To examine this, we administered H3 receptor agonist α-methylhistamine ( 10mg/kg), histamine H3 receptor antagonist thioperamide (5mg/kg) or physiological saline intraperitoneally in rats and its effects on degranulation of submucosal glands were evaluated by Alcian blue/periodic acid-Schiff (AB/PAS) staining. Thioperamide significantly induced degranulation in the submucosal gland in the nasal septum compared with the methylhistamine group and the control group. These results suggest that histamine H3 receptors play some roles in mucus secretion in submucosal gland in the nose.