Trypan blue as an indicator of urothelial integrity

Defects in the urinary bladder urothelium may be an etiological factor in conditions such as recurrent urinary tract infection and interstitial cystitis. Initial studies have demonstrated that the colloidal dye trypan blue can be used as a marker for defects in the integrity of the mucosal epithelium. Male white New Zealand rabbits were separated into 4 groups: Control, in vivo overdistension (via saline infusion), intravesical acetone (20 ml 50% for 1 minute), and intravesical 50% DMSO (20 ml “RIMSO-50” for 30 minutes). Both intravesical instillations were followed by 3–20 ml saline washes. Immediately following acetone or DMSO, 20 ml 1% trypan blue in saline was instilled and left in the bladder for up to 1 hour. After overdistension, 1% trypan blue in saline was infused into the bladder at the same rate until the volume reached that previously defined as the overdistension volume. Control bladders were rinsed with 20 ml saline, twice, before being filled with 20 ml of the trypan blue solution. There was no evidence of trypan blue's staining of tissues in any of the control bladders. After DMSO treatment, there was usually only slight staining of the bladder surface urothelium and subjacent connective tissues. After acetone treatment, microscopic examination of bladder wall showed that nuclei were stained in all tissues of the wall (e.g., urothelium, connective tissue and smooth muscle). After acute frank overdistension, the bladder wall was deep blue throughout, very similar to the acetone-treated bladder. Microscopic analysis demonstrated that the smooth muscle elements were the most heavily stained. In summary 1) trypan blue does not penetrate the normal bladder mucosa, nor is any dye absorbed into the blood stream. 2) Frank overdistension of the bladder defeats the physical integrity of the urothelium as evidenced by penetration of the dye into the submucosal tissue, the peritoneal cavity, and bloodstream. 3) Where DMSO penetrates the urothelium itself, it appears to leave no permanent route by which other molecules can traverse the urothelium after it is removed. 4) Only after the integrity of the urothelial surface is disturbed are the cells of the urothelium susceptible to staining.