Interactions between A-9THC and capsaicin on isolated lamb bladder detrusor

A number of studies have demonstrated that capsaicin, a capsicum alkaloid, can affect isolated bladder tissue with either a relaxation or a contraction, depending on the species, by acting on VR1 receptors. In a previous work on isolated lamb detrusor, we demonstrated that capsaicin generally produces a relaxation of the tissue; this relaxation seems to be mediated by CGRP. Endogenous cannabinoids, such as anandamide, produce some of their actions by stimulating VR1 receptors and this seems to cause the release of peptides, e.g. CGRP. The aim of this work was to ascertain whether a cannabinoid, delta-9-tetrahydrocannabinol (delta-9THC), was able to interfere with the response of the isolated lamb detrusor to capsaicin. A-9THC, at concentrations between 1.6 x 10(-7) and 1.3 x 10(-6) M, displayed no activity on tissues. Instead, following delta-9THC, most of the tissues responded to capsaicin with a contraction that was abolished by atropine (9.0 x 10(-7) M). It has been reported that cannabinoids can inhibit the release of CGRP by stimulation of CB1 and CB2 cannabinoid receptors. Delta-9THC could act stimulating these receptors and thus inhibiting CGRP release and vesical relaxation. The muscle relaxing component removal could favour the contracting component, usually not active.