Do nasal mast cells release histamine on stimulation with substance P in allergic rhinitis

Summary The effects of nasal administration of increasing doses of exogenous substance P have been studied in patients with allergic rhinitis treated with placebo or with the H 1 antagonist cetirizine (10 mg twice daily for 3 days). Responses to substance P were assessed by posterior rhinomanometry (measuring nasal airway resistance) and by measure of histamine, protein and albumin production and cell recovery in nasal lavage fluids before and after challenge. Substance P induced a dose-dependent increase in nasal airway resistance which was similar after treatment with either cetirizine or placebo (maximal increase in nasal airway resistance was 4·2-fold greater than the baseline with the placebo and 4·7-fold greater than the baseline with cetirizine). No histamine release was observed. Similar increases in protein and albumin production were observed after stimulation with substance P along with the placebo (protein: from 0·35±0·11 to 3·31±0·62 mg and albumin: from 0·09±0·04 to 2·08±0·39 mg) and when combined with cetirizine treatment (proteins: from 0·42±0·09 to 3·62±0·77 and albumin: from 0·17±0·04 to 2·19±0·51 mg). After stimulation with substance P, percentages of neutrophils recovered in nasal fluids increased from 26·2±11·5 to 54·5±9.5 with the placebo and from 35·5±11·0 to 53·6±9·5 with cetirizine. Eosinophils were inconsistently found after substance P stimulation during both treatments. In conclusion, nasal response to substance P is not modified by cetirizine which suggests that the effect of substance P is not secondary to histamine release in the nose in man.