Stimulation of guinea‐pig tracheal afferent fibres by non‐isosmotic and low‐chloride stimuli and the effect of frusemide.

Abstract

1. Inhalation of low‐chloride or non‐isosmotic solutions evokes cough or reflex bronchoconstriction in humans that is inhibited by frusemide (furosemide), whilst capsaicin‐evoked cough is unaffected. Here we have examined the responses of single vagal afferent fibres innervating the isolated guinea‐pig trachea to these stimuli, and tested the effect of frusemide on fibre responses. 2. Both distilled water and hypertonic saline applied for 30 s onto identified receptive fields produced marked excitation of all A delta and C fibres tested. Isotonic glucose, a low‐chloride solution, was a less potent stimulant and caused excitation in 37% of A delta fibres and 69% of C fibres. There was no difference in the distribution of low‐chloride sensitive and insensitive receptive fields. 3. In the presence of frusemide, responses of A delta fibres to isotonic glucose were significantly inhibited to 34.2 +/‐ 6.2% of the pre‐drug control level. However, frusemide was without effect either on responses of A delta fibres to distilled water or hypertonic saline, or on responses of C fibres to capsaicin. 4. These data support a role for tracheo‐bronchial A delta and C fibres in airway reflexes evoked by hypotonic, hypertonic and low‐chloride stimuli. The protective effect of frusemide against airway responses to low‐chloride but not to non‐isosmotic solutions may reflect an action on sensory nerve endings. © 1995 The Physiological Society