A UNIQUE NEW MODEL TO STUDY THE EFFECTS OF URINARY-DIVERSION IN THE DEVELOPING RABBIT BLADDER

Purpose: Little is known about the developmental effects of high urina ry diversion and bladder defunctionalization in infancy. Although clin ical experience shows that a poorly functional bladder may result from urinary diversion in infancy, the mechanisms of change and specific b ladder wall alterations have not been well characterized. We hypothesi zed that cyclic filling and emptying are necessary for normal bladder development. To investigate this important question we created a new a nimal model. Materials and Methods: We designed a new method of hemibl adder urinary diversion in 3-week-old New Zealand white rabbits. After vertical midline bladder division half of the bladder was formed into a functional reservoir, which remained in continuity with the ipsilat eral ureter and urethra. The other bladder half was defunctionalized a nd isolated from the urine flow by ureteral ligation. Diversion was cr eated for 3, 7, 14 and 28 days. Urodynamic evaluation was done in the functionalized hemibladders and age matched normal rabbit bladders to test the validity of the functionalized hemibladder as an internal con trol. Functional and defunctionalized hemibladders as well as age matc hed, nonoperated normal rabbit bladders were weighed, sectioned and st ained to demonstrate muscle and connective tissue components. Results: In 22 of the 27 healthy rabbits (81%) good quality diverted and funct ional bladder specimens were obtained after diversion. Defunctionalize d hemibladders grew more slowly than functionalized bladders and norma l age matched control bladders. Histological staining of the bladder w all demonstrated increased connective tissue between the muscle bundle s within the diverted specimens than in functional bladders. Conclusio ns: Our successful model of urinary diversion may be used to study the developmental and histological effects of urinary diversion in the yo ung bladder. Bladder growth and histological appearance are altered wh en the stimulus of cyclic filling and emptying is removed. Further stu dies using this model are warranted to define fully bladder changes th at result from diversion and investigate the mechanism of the observed changes.