Nasal challenge with serotonin in asymptomatic hay fever patients.

To study the nasal response to serotonin, 14 asymptomatic hay fever patients received intranasal serotonin in increasing doses. Itching and the number of sneezes were noted, and the amount of secretion was measured and assayed for substance P. Nasal airway resistance was recorded by active posterior rhinomanometry. Serotonin induced a dose-dependent increase in nasal itching, number of sneezes and secretion. Substance P was found in 41 of 42 secretions. The median concentration was 10.3 pmol/l (range 0-28.9), and increased parallel to increasing doses of serotonin (P less than 0.001).