Stimulation of guinea-pig tracheal afferent fibres by non-isosmotic and low-chloride stimuli and the effect of frusemide.
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.
Fox
A J
AJ
Department of Thoracic Medicine, National Heart and Lung Institute, London, UK.
Barnes
P J
PJ
Dray
A
A
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology*; D005260:Female; D005665:Furosemide / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009412:Nerve Fibers / Q000187:drug effects* / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects* / Q000502:physiology; D014132:Trachea / Q000187:drug effects / Q000294:innervation*; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology
D002712:Chlorides; D005665:Furosemide; D002211:Capsaicin