Changes of the Urothelial Barrier System in the Cyclophosphamide-Induced Cystitis in Rats by Using a Newly Established "Inside-Out" Urinary Bladder Preparation.

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The study was aimed to establish the "inside-out" preparation with the urothelium and investigate the changes in urothelial permeability of the cyclophosphamide (CYP)-induced cystitis model in rats. In female rats with or without CYP injection, the isolated whole bladder was utilized as an "inside-out" preparation with the urothelium, which was created by reversing the bladder from a top portion. The preparation was fixed in the organ bath, and instilled with a Krebs solution (0.5 mL) through the bladder neck. After it was kept under an isovolumetric condition, high K+ (KCl: 50 mM) or acetylcholine (ACh: 10 μM) was added into the organ bath. In the normal bladder, the intravesical pressure of the inside-out preparation with the urothelium did not change with the addition of KCl or ACh. Contrarily, in the CYP-injected bladder 24 or 48 h after injection of CYP, the intravesical pressure of the inside-out preparation increased with the addition of KCl or ACh. Histological examinations showed a denuded and/or cracked surface of the urothelial layer, and the intensity of uroplakin III staining of the urothelial layer decreased in the CYP-injected rats. The study demonstrated the bladder urothelium has robust barrier mechanisms for preventing the absorption of water (urine) under the normal condition. However, these barrier mechanisms were disrupted in the CYP-induced cystitis, suggesting that water and urine insults can be permeabilized into the urinary bladder, specifically to the smooth muscle layer.