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Capsaicin‐induced bronchoconstriction in the guinea‐pig: contribution of vagal cholinergic reflexes, local axon reflexes and their modulation by BW443C81
Author(s) -
Buchan P.,
Adcock J.J.
Publication year - 1992
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1992.tb14273.x
Subject(s) - capsaicin , atropine , vagotomy , bronchoconstriction , chemistry , cholinergic , axon reflex , reflex , cough reflex , anesthesia , vagus nerve , nalorphine , endocrinology , medicine , (+) naloxone , opioid , receptor , stimulation , airway
1 The objective of the study was to investigate the central vagal and local axon reflex components of bronchoconstrictor responses evoked by inhalation of capsaicin aerosol in anaesthetized guinea‐pigs. This was accomplished by comparing the effects of bilateral vagotomy, atropine and the peripherally‐acting polar enkephalin analogue, BW443C81, on bronchoconstrictor responses evoked by capsaicin. The effects of codeine were also determined. 2 Aerosols of capsaicin were generated from a 0.9 μg ml −1 solution. Inhalation of capsaicin aerosol in 5, 10 and 15 breaths evoked dose‐related bronchoconstrictor responses. The responses were immediate in onset and of extended duration. 3 Capsaicin‐induced bronchoconstrictor responses were significantly inhibited following bilateral vagotomy or atropine (0.3 mg kg −1 , i.v.) pretreatment by 46% ± 14% ( P < 0.05) and 59% ± 13% ( P < 0.01), respectively. 4 Administration of BW443C81 by intravenous infusion (3, 30 and 100 μg kg −1 min −1 ) caused a significant inhibition of capsaicin‐induced bronchoconstrictor responses which achieved a greater maximum than either bilateral vagotomy or atropine. Codeine (100 μg kg −1 min −1 , i.v.) did not significantly inhibit the bronchoconstrictor responses. 5 Inhibition of capsaicin‐induced bronchoconstrictor responses by BW443C81 (30 μg kg −1 min −1 , i.v.) was significantly ( P < 0.05) reduced by the peripherally‐acting opioid antagonist N‐methyl nalorphine (100 μg kg −1 min −1 , i.v.). 6 These results show that capsaicin‐induced bronchoconstrictor responses are mediated by at least two mechanisms, a vagal and/or cholinergic reflex pathway and a non‐cholinergic pathway. BW443C81, but not codeine, significantly inhibited ( P < 0.005) both mechanisms of capsaicin‐induced bronchoconstriction probably by an action on peripheral opioid receptors located on vagal sensory nerves.