A possible role of lipoxygenase in the activation of vanilloid receptors by anandamide in the guinea‐pig bronchus

The vanilloid receptor antagonist, capsazepine (10 μM), significantly attenuated the contractile effect of anandamide, the response to 100 μM anandamide being 40.53±7.04% in the presence of vehicle and 1.57±8.93% in the presence of 10 μM capsazepine. The contractile actions of anandamide and AM404 were markedly enhanced by the peptidase inhibitor thiorphan.

The log concentration‐response curve of anandamide was unaltered by the CB₁ receptor antagonist, SR141716A. The pEC₅₀ values for anandamide were 4.88±0.08 and 5.17±0.19 in the presence of vehicle and SR141716A (1 μM) respectively.

The lipoxygenase inhibitors 5,8,11,14‐eicosatetraynoic acid (ETYA) and 5,8,11 eicosatriynoic acid (ETI) reduced the effect of 100 μM anandamide from 34.7±1.9% (vehicle) to 7.7±5% (ETYA, 10 μM) and from 41.85±4.25% (n=6) (vehicle) to 10.31±3.54 (n=6) (ETI, 20 μM). Neither inhibitor significantly affected contraction of the tissue by substance P.

This study provides evidence that anandamide acts on vanilloid receptors in the guinea‐pig isolated bronchus. These data raise the possibility that the contractile action of anandamide may be due, at least in part, to lipoxygenase metabolites of this fatty acid amide that are vanilloid receptor agonists.