Recent animal studies have found that nociceptin can inhibit cough responses induced by capsaicin. We hypothesize that sputum and plasma levels of these peptides may reflect some neurochemical alterations in airway cough reflex or neurogenic inflammation in asthma or COPD. The aims of this study are to investigate the association between sputum and plasma levels of nociceptin and substance P with cough severity and airway hyperreactivity in patients with asthma, COPD and chronic cough. We will enroll 260 patients (100 patients with asthma, 60 with COPD and 100 with chronic cough) as well as 40 healthy subjects for this study. Sputum and peripheral blood will be collected and concentrations of nociceptin and substance P will be measured by ELISA. These levels will be correlated with cough severity (symptom scores), and airway hyperresponsiveness to inhaled methacholine as measured by PC20. Sputum and plasma concentrations of both peptides will be rechecked after clinical improvements in cough or airway symptoms are achieved after therapy.
