Functional and Immunohistochemical Characterization of CB1 and CB2 Receptors in Rat Bladder

ObjectivesTo 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).MethodsWhole 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.ResultsImmunofluorescence 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.ConclusionsCB1 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.