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OBJECTIVE To investigate the expression of muscarinic and purinergic receptors in rat urothelium, and changes in their distribution and expression following detrusor overactivity induced by bladder outlet obstruction (BOO). MATERIALS AND METHODS Thirty Sprague-Dawley rats were divided into control (10) and BOO groups (20). Partial BOO was induced for 3 weeks and the rats assessed by cystometrography. A portion of the bladder was stained using immunofluorescence for M2 and M3 muscarinic receptors, and P2X3 purinergic receptors. The remainder was dissected into bladder urothelium and the smooth muscle layer, and the expression of the receptor proteins analysed by Western blotting. RESULTS Cystometrography showed a significant decrease in contraction interval and increase in contraction pressure in the BOO group. On immunofluorescence staining, muscarinic and purinergic receptors were localized in both the urothelium and the muscle layer. Immunoreactivity of M2 and M3 muscarinic receptors was greater in the urothelium of the BOO group than in the control group; there was a smaller increase in P2X3 immunoreactivity. On Western blotting, the expression of M2, M3 and P2X3 receptors was increased in the urothelium of the BOO group, and there was increased M3 receptor expression in the muscle layer of the BOO group. CONCLUSIONS There were detectable changes in muscarinic and purinergic receptors with bladder overactivity induced by BOO. Our results suggest that changes in urothelium receptor expression could have a role in mediating the afferent sensory responses in the urinary bladder. [ABSTRACT FROM AUTHOR]