CAPSAICIN TREATMENT INDUCES MUSCARINIC HYPERREACTIVITY IN GUINEA-PIG TRACHEA - A WARNING

Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is a widely used tool for the depletion of neuropeptides from sensory C-fibres. Upon capsaicin treatment tachykinins are released, resulting in a variety of response s in the airways. We showed that after capsaicin (0.3 mu M; 30 min) tr eatment of guinea pig tracheal smooth muscle preparations, the maximal contraction of the trachea after methacholine stimulation was strongl y increased (capsaicin: 1.147 +/- 0.050 g vs. control: 0.717 +/- 0.047 g). This effect was completely nullified after pretreatment with caps azepine -7,8-dihydroxy-2,3,4,5-tetrahydro-1H-2benzazepine; a vanilloid receptor antagonist) and YM38336 (a dual tachykinin NK1 and tachykini n NK2 receptor antagonist). Our results serve as a warning against usi ng capsaicin as a putatively clean pharmacological tool to deplete the neuropeptides from pools on the C-fibres because we showed that capsa icin also strongly influences basal mechanisms in tracheal smooth musc le control. (C) 1998 Elsevier Science B.V.