Substance P, Calcitonin Gene-related Peptide, and Vasoactive Intestinal Peptide Increase in Nasal Secretions After Allergen Challenge in Atopic Patients

Background: There is suggestive evidence that neuropeptides participate in allergic reactions. Substance P (SP) and calcitonin gene-related peptide (CGRP) are released by sensory nerves, whereas vasoactive intestinal peptide (VIP) is released mainly by parasympathetic nerves. Both sets of nerves are thought to be stimulated by allergic inflammation. The aim of this study was to assess nasal secretions to determine whether SP, CGRP, and VIP were increased after allergen challenge.

Methods: Eight patients with allergic rhinitis were challenged nasally with 1 mg histamine or increasing doses of allergen. Nasal lavages were collected into a cocktail of protease inhibitors in order to restrict neuropeptide degradation. Radioimmunoassay for SP, CGRP, and VIP were performed on each sample.

Results: All patients had immediate clinical reactions to both histamine and allergen challenges, and seven patients experienced a later allergic reaction. After histamine challenge, SP and CGRP did not increase significantly above baseline in the nasal lavages, whereas VIP did (p < 0.02). In contrast, SP, CGRP, and VIP all significantly increased immediately after allergen challenge and returned to baseline within 2 hours. At the clinical peak of the late allergic reaction, SP, but not CGRP or VIP, was increased slightly but significantly (p < 0.01).

Conclusions: Thus SP, CGRP, and VIP are found in nasal secretions after allergen challenge, which confirms that neuropeptides are released in human beings during allergic reactions. The selective stimulation of VIP secretion by histamine challenge suggests that histamine-induced cholinergic reflexes induce the release of VIP. These data support the suggestion that neuropeptides may be partly responsible for some of the nasal symptoms of allergy.