Urothelial permeability of the isolated whole bladder

The urothelium of the bladder presents an effective barrier to the penetration of solutes from the urine into the bladder wall. Previously, we have demonstrated that the dye indigocarmine can be utilized intravesically to study urothelial permeability. In general, intravesical indigocarmine (administered in vivo) will not penetrate the bladder wall unless the urothelium is damaged by overdistension, acetone administration, or mechanical damage. Unfortunately, using in vivo methodologies, one is limited in the study of the effect of specific conditions and permeations on bladder permeability. In the current study an isolated in vitro whole bladder model was developed to quantitatively study the permeability of the bladder urothelium. In these studies, the penetration of indigocarmine into and through the bladder wall was quantitated under various conditions. The in vitro bladder was filled by infusing 1% indigocarmine in saline in a step‐wise manner at the rate of 10 ml in 10 minutes followed by a stabilization period of 10 minutes. Samples were taken from the bath at 20 minutes intervals for spectrophotometrical analysis of the dye. At the end of experiment the bladder was washed in saline for 10 minutes, and stored and extracted in formalin. In general, no indigocarmine penetrated the urothelium until the in vitro capacity was reached and exceeded. At intravesical volumes greater than capacity, the dye concentration in the bath increased very rapidly, even though the integrity of the bladder wall remained intact. In bladders treated with a gentle 50% acetone wash for 1 minute the dye started to penetrate into the bath at intravesical volumes of 25% of capacity and increased rapidly thereafter. Heparin instillations both delayed the onset of dye penetration and reduced the magnitude of the dye penetration. In addition, heparin inhibited dye penetration only at low volumes. Although in vitro anoxia of 60 minutes induced only slight dye penetration into the bath, the dye concentration in the tissue increased substantially indicating that anoxia induced damage to the urothelium.