Alterations of M ₂,₃ -Muscarinic Receptor Protein and mRNA Expression in the Bladder of the Fructose Fed Obese Rat

PURPOSE: The effects of metabolic syndrome on bladder function and M2,3-muscarinic receptor expression were studied using the fructose fed obese rat. MATERIALS AND METHODS: Male Wistar rats were divided into 2 groups, including group 1-normal control rats and group 2-6-week fructose fed rats. In vivo cystometry using anesthesia was performed. In vitro the bladder was divided into the urothelium and muscle layer by microdissection. Tissue M2,3-muscarinic receptor protein levels were measured by Western blotting. Expression of the mRNAs that encode M2,3-muscarinic receptors was estimated using reverse transcriptase-polymerase chain reaction. RESULTS: Premicturition unstable bladder contractions suggestive of detrusor overactivity were noted in 62.5% of fructose fed rats but in no controls. M2,3-muscarinic receptor protein and mRNA expression was noted in the urothelium and muscle layer of the rat bladder. In control rats the M2-to-M3-muscarinic receptor protein expression ratio was 1:0.68 in urothelium and 1:0.28 in the muscle layer, and that for mRNA expression was 1:0.32 and 1:0.36, respectively. Compared to controls bladder M2,3-muscarinic receptor protein expression in the urothelium and muscle layer of 8 preparations each was significantly increased in fructose fed rats by 89% and 90% for M2-muscarinic receptor (each p <0.001), and by 35% and 93% for M3-muscarinic receptor (p <0.01 and <0.001, respectively). Correspondingly M2,3-muscarinic receptor mRNA expression in the fructose fed rat bladder urothelium and muscle layer of 8 preparations each was also significantly increased by 31% and 49% for M2-muscarinic receptor (each p <0.01), and by 121% and 117% for M3-muscarinic receptor (each p <0.001, respectively). CONCLUSIONS: Metabolic syndrome induces increased expression of M2,3-muscarinic receptor mRNA and protein in the urothelium as well as the muscle layer of the bladder in 6-week fructose fed rats. The receptor alterations are associated with functional evidence of detrusor overactivity.