To determined the localization of CB₁ and CB₂ receptors in rat bladder and investigate the effect of a mixed CB₁/CB₂ receptor agonist, ajulemic acid (AJA), on chemically evoked release of the sensory neuropeptide calcitonin gene-related peptide (CGRP).

Whole rat bladders were incubated in a series of tissue baths containing physiologic salt solution to measure baseline CGRP release by enzyme immunoassay. Capsaicin (30 nM) and adenosine triphosphate (10 μM) were used to provoke CGRP release in the presence or absence of AJA. Specificity of AJA for CB₁ and CB₂ receptors was determined using antagonists. Localization was determined by immunofluorescence for CB₁ and CB₂ receptors in fixed bladders.

Immunofluorescence showed the localization of CB₁ and CB₂ receptors in the bladder. Mean baseline CGRP release was 605 ± 62 pg/g of bladder weight, and AJA had no effect on CGRP release. The addition of adenosine triphosphate/capsaicin significantly increased the CGRP release over baseline, by 44% (P < .05), and AJA application significantly decreased CGRP release, by 29% compared with controls (P < .05). The CB₁ and CB₂ antagonists AM 251 and AM 630, respectively, reversed the blunting effect of AJA on evoked CGRP release, resulting in an increase of 40% and 38% over baseline, respectively.

CB₁ and CB₂ receptors are localized in the urothelium of rat bladder, and application of AJA inhibits the evoked release of CGRP by acting on CB₁ and CB₂ receptors. These findings identify a potential new pathway for study in the evaluation and treatment of painful bladder syndrome/interstitial cystitis.