1.
Kallidin (5-500 nmol), hypertonic
saline (0.9-20% NaCl) or low pH medium (
citric acid: pH 2.5-1) applied (50 microliters) to the human nasal mucosa produced a
pain response (evaluated by a visual analogue scale) that was related to the concentration of the
peptide, NaCl or
hydrogen ions, respectively. 2. Application (50 microliters) of
capsaicin (50 nmol) to the human nasal mucosa produced overt
pain. After repeated administrations (once a day for 5-7 days) to one nostril this effect underwent almost complete desensitization, while in the contralateral nostril, treated with the vehicle, the response to
capsaicin was unaffected. 3. The
pain response produced in the human nasal mucosa by topical application (50 microliters) or
kallidin (50-500 nmol), NaCl (10-20%) or
citric acid (pH 1.5-1) solutions was then studied before and after local
capsaicin desensitization. 4. The
pain response to pH 1.5 or 1
citric acid was markedly reduced (by 60% and 75%, respectively) in the
capsaicin-treated nostril. However, the
pain response to 10% or 20% NaCl or the mild
pain response to 50 or 500 nmol
kallidin were unaffected by
capsaicin pre-treatment. 5. The present results suggest that prolonged topical
capsaicin treatment to the human nasal mucosa may lead to selective desensitization to certain algesic stimuli such as
capsaicin itself and
hydrogen ions.