Nasal response to substance P and methacholine in subjects with and without allergic rhinitis.

We compared the rise in nasal airway resistance (NAR) provoked by topical application of substance P (SP) and of methacholine (MCH) in seventeen patients suffering from rhinitis and fourteen control subjects. Challenges with SP or MCH were separated by a week or more. NAR was measured by posterior rhinomanometry before and 10 min after intranasal administration of SP (10-40 nmol) or MCH (3-12 mumol). The two groups of subjects had similar baseline levels of NAR and similar small responses to buffered saline. Substance P but not MCH provoked cutaneous flushing in all subjects. Both SP and MCH provoked a significantly greater increase in NAR in patients suffering from rhinitis than in control subjects. The increase in NAR was dose-dependent, and on a molar basis, SP was 375-500-fold more potent than MCH. Pretreatment with 200 micrograms of a topically active anticholinergic agent, oxytropium bromide, prevented the rise in NAR caused by 12 mumol of MCH but not that caused by 40 nmol of SP in six patients suffering from rhinitis. We conclude that SP is absorbed across the nasal mucosa and causes cutaneous vasodilation, that MCH and SP cause a greater rise in NAR in patients suffering from rhinitis than in control subjects, that SP is about 500-fold more potent than MCH in increasing NAR, and that the rise in NAR caused by SP is not mediated by postganglionic parasympathetic mechanisms.