Complex respiratory effects of nebulised citric acid and capsaicin as tussive agents: A comparative study in conventional and specific pathogen-free guinea pigs.

Abstract

BACKGROUND: Citric acid and capsaicin are commonly used in cough research due to their reproducible effects on animal models and humans. However, these extend beyond cough provocation. OBJECTIVE: To characterize and describe the respiratory responses to citric acid and capsaicin exposure using whole-body plethysmography in conventional (CON) and specific pathogen-free (SPF) guinea pigs. METHODS: Male and female guinea pigs were exposed to aerosols of saline, citric acid (0.4 M), and capsaicin (25 µM). Cough and respiratory parameters (inspiratory and expiratory time, respiratory rate, tidal volume, enhanced pause and mid-expiratory flow) were recorded. RESULTS: Both tussive agents induced upper and lower airway responses besides cough, with significant differences in respiratory parameters between CON and SPF animals. Citric acid elicited a stronger upper airway response compared to capsaicin. CONCLUSION: Citric acid and capsaicin trigger complex respiratory responses (bronchoconstriction, braking, breathing pattern changes). These findings highlight the need to consider broader respiratory responses in translational cough research.