Chronic tobacco smoke exposure increases cough to capsaicin in awake guinea pigs

Abstract

Chronic exposure to irritants such as tobacco smoke (TS) can induce spontaneous and enhanced irritant-induced coughing, especially in asthma. To determine if the mechanism of enhanced coughing involves activation of capsaicin-sensitive sensory receptors (C-fibers), we exposed both non-sensitized (NS) and ovalbumin-sensitized guinea pigs to TS (5 mg/L air, 30 min exposure, and 7 days/week). Similar groups were exposed to compressed air. After 90 days of exposure, we challenged the airways with capsaicin, bradykinin, histamine and methacholine. Capsaicin induced coughing as well as bronchoconstriction in guinea pigs exposed to TS. In ovalbumin (OA) guinea pigs coughing and bronchoconstriction were enhanced. Tachykinin receptor antagonists attenuated coughing to both capsaicin and acute TS challenge. Bradykinin also induced coughing and bronchoconstriction in guinea pigs exposed to TS. There was no statistical separation between the two TS groups however. Histamine and methacholine induced similar bronchoconstriction but fewer coughs in all four experimental groups. In conclusion, chronic TS exposure induced coughing to capsaicin and bradykinin challenge. The effect of capsaicin was further enhanced in OA guinea pigs. Enhanced coughing induced by TS exposure likely involves activation of capsaicin-sensitive sensory C-fibers and neuropeptide release with possible subsequent activation of rapidly-adapting receptors.