Objective: To investigate diabetes-associated changes in urinary bladder expression of cannabinoid receptors 1 and 2 (CB1 and CB2) and the functional role of CB agonists and antagonists in mediating phasic contractions of isolated bladder strips using a streptozotocin-induced diabetic rat model.
Materials and methods: The bladder and dorsal root ganglion (DRG) were removed from diabetic rats and age-matched controls 8-10 weeks after diabetes induction. Expression of CB1 and CB2 mRNA was studied using quantitative real-time PCR and protein levels were determined by Western blot analysis. The effect of increasing concentrations (0.1-100 μM) of the mixed CB1/CB2 agonist R(+)-WIN 55,212-2 (WIN), selective CB1 antagonist (AM251) and selective CB2 antagonist (AM630) on carbachol-evoked contraction of bladder strips from control and diabetic rats was investigated. WIN-induced alterations of bladder strip contraction were then studied after pre-incubation with AM251 and AM630.
Results: Diabetes induced decreased CB1 protein and mRNA expression in both the bladder and DRG (P < 0.05), while decreased CB2 expression was observed in the bladder (P < 0.05). WIN decreased the amplitude, but not frequency, of carbachol-induced phasic contractions of bladder strips in a concentration-dependent manner and this effect was diminished in the diabetic state. AM630 and AM251 had no effect on isolated detrusor muscle function. Moreover, pre-incubation with AM251 partially counteracted the effect of WIN on detrusor muscle contraction.
Conclusion: The results indicate that CB1 and CB2 are responsible for the pathogenesis of bladder dysfunction in diabetes mellitus and represent a viable target for pharmacological treatment of bladder cystopathy.
© 2013 BJU International.