Increased tachykinin levels in induced sputum from asthmatic and cough patients with acid reflux.

BACKGROUND: Acid reflux may aggravate airway disease including asthma and chronic cough. One postulated mechanism concerns a vagally-mediated oesophageal-tracheobronchial reflex with airway sensory nerve activation and tachykinin release. AIM: To test the hypothesis that patients with airways disease and reflux have higher airway tachykinin levels than those without reflux. METHODS: Thirty-two patients with airways disease (16 with mild asthma and 16 non-asthmatic subjects with chronic cough) underwent 24 h oesophageal pH monitoring. Acid reflux was defined as increased total oesophageal acid exposure (% total time pH<4 of >4.9% at the distal probe). All subjects underwent sputum induction. Differential cell counts and concentrations of substance P (SP), neurokinin A (NKA), albumin and alpha2-macroglobulin were determined. RESULTS: SP and NKA levels were significantly higher in patients with reflux than in those without (SP: 1434 (680) pg/ml vs 906 (593) pg/ml, p=0.026; NKA: 81 (33) pg/ml vs 52 (36) pg/ml, p=0.03). Significantly higher tachykinin levels were also found in asthmatic patients with reflux than in asthmatic patients without reflux (SP: 1508 (781) pg/ml vs 737 (512) pg/ml, p=0.035; NKA: median (interquartile range 108 (85-120) pg/ml vs 75 (2-98) pg/ml, p=0.02). In patients with asthma there was a significant positive correlation between distal oesophageal acid exposure and SP levels (r=0.59, p=0.01) and NKA levels (r=0.56, p=0.02). Non-significant increases in SP and NKA were measured in patients with cough with reflux (SP: 1534.71 (711) pg/ml vs 1089 (606) pg/ml, p=0.20; NKA: 56 (43) pg/ml vs 49 (17) pg/ml, p=0.71). No significant difference in differential cell counts or any other biochemical parameter was noted between study groups. CONCLUSION: This study demonstrates increased airway tachykinin levels in patients with asthma and cough patients with coexistent acid reflux. This suggests airway sensory nerve activation in this population.