Prostanoids and cough response to capsaicin in asthma and chronic bronchitis.

Cyclooxygenase products are released by chronic airway inflammation. Our working hypothesis for the present study was that prostanoids augment airway cough sensitivity. The effects of a cyclooxygenase inhibitor, indomethacin (100 mg.day-1 for 4 days), and a thromboxane synthesis inhibitor, OKY-046 (400 mg.day-1 for 4 days), on cough response to inhaled capsaicin were examined in eight patients with asthma, 10 patients with chronic bronchitis, and 10 normal subjects. Capsaicin cough threshold, the lowest concentration of capsaicin eliciting five or more coughs, was measured as an index of airway cough sensitivity. In asthmatics, the cough thresholds with indomethacin treatment (15.7 (GSEM 1.38) microM) and OKY-046 (10.2 (GSEM 1.20) microM) were significantly greater than the value with placebo (6.05 (GSEM 1.25) microM). In patients with chronic bronchitis, the cough threshold was significantly greater with indomethacin (5.94 (GSEM 1.50) microM) than with placebo (3.41 (GSEM 1.33) microM and OKY-046 2.97 (GSEM 1.43) microM). In normal subjects, the capsaicin cough threshold was not altered by indomethacin or OKY-046 treatment. These results support our hypothesis and suggest that thromboxane A2 may be one of the cyclooxygenase products augmenting airway cough sensitivity in asthma, but not in chronic bronchitis.