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

Abstract

OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.