The endogenous cannabinoid agonist, anandamide stimulates sensory nerves in guinea-pig airways

1 The endogenous cannabinoid agonist, anandamide produced a modest contractile response in guinea-pig isolated bronchus compared with the vanilloid receptor agonist capsaicin. The contractile response to both anandamide and capsaicin was inhibited by the vanilloid receptor antagonist, capsazepine. Furthermore, the NK2-selective antagonist, SR48968 but not the NK1-selective antagonist, SR140333 inhibited contractile responses to anandamide. 2 The contractile response to anandamide was abolished in tissues desensitized by capsaicin. However, anandamide failed to cross-desensitize the contractile response to capsaicin. 3 The contractile response to anandamide was not significantly altered in the presence of the CBI receptor antagonist, SR141716A, nor the amidase inhibitor, phenylmethylsulphonyl fluoride (PMSF) but was significantly increased in the presence of the neutral endopeptidase inhibitor, thiorphan. 4 The cannabinoid agonist, CP55,940 failed to significantly attenuate the excitatory non-adrenergic non-cholinergic (eNANC) response in guinea-pig airways. In contrast, the ORL1 receptor agonist, nociceptin, significantly inhibited this response. 5 The results demonstrate that anandamide induces a modest contractile response in guinea-pig isolated bronchus that is dependent upon the activation of vanilloid receptors on airway sensory nerves. However, cannabinoid receptors do not appear to play a role in this regard, nor in regulating the release of neuropeptides from airway sensory nerves under physiological conditions.