Effects of mild bladder outlet obstruction on rabbit bladder structure and function.

Mild bladder outlet obstruction was created in 42 New Zealand white rabbits by placing a 5-mm inner diameter polyethylene tube around the urethra. Periods of obstruction lasted for 1 day (7 rabbits), 3 days (7 rabbits), 1 week (7 rabbits), 2 weeks (6 rabbits), 4 weeks (7 rabbits), 6 weeks (4 rabbits) and 8 weeks (4 rabbits). Whole bladder functional study was performed in control (5 rabbits) and the obstructed bladders. The obstructed bladders increased in weight two-to threefold. There was no significant difference in bladder weight after different periods of obstruction. Electric stimulation showed a diminished response after 3 days of obstruction. Pharmacologic stimulation with 500 microM carbachol revealed a decreased response after obstruction, but intravesical pressure returned to the control level at 6 and 8 weeks of obstruction. However, the bladder weight and the expelling function of the obstructed bladders remained the same as on day 1 of obstruction. Histologic study of control and obstructed bladders revealed that: 1) dense submucosal fibrous tissue developed after 3 days of obstruction, 2) detrusor muscle hypertrophy and hyperplasia were noted with intermuscular collagenous fiber deposition after 2 weeks of obstruction, 3) trabeculation of the bladder wall with hyperplasia of muscular bundles was noted after 2 weeks of obstruction, 4) acute edematous and inflammatory reaction were apparent after 3 days and 1 week of obstruction, but resolved later and 5) degenerative changes of muscular cells were noted at 8 weeks of obstruction. The results show that despite apparent morphologic changes after outlet obstruction, no significant difference was observed in bladder expelling between short-term and long-term infravesical mild outlet obstruction. The bladder contractile apparatus appears to have a compensatory ability after mild outlet obstruction.