Bladder dysfunction after acute urinary retention in the rats: a novel over active bladder model

As there is increasing evidence that benign prostatic hyperplasia and its related acute urinary retention (AUR) induce over active bladder (OAB) syndrome, we investigated the effects of AUR on bladder function over a 4-week period in a rat model. Ten-week-old female Sprague-Dawley rats were used in this study. AUR was induced by clamping the distal urethra of each rat with a small clip, and then infusing 3 ml (0.6 ml/min) of saline with an infusion pump through a transurethral catheter (22G). The obstruction was sustained for 60 min and the clip was removed and then the bladder was allowed to drain through the catheter. The bladder function was estimated by voiding behavior studies (at 3 days, 1, 2, 3, and 4 weeks), cystometric studies (at 2 and 4 weeks) and organ bath studies using KCl and carbachol (at 2 and 4 weeks). Furthermore, we evaluated histological changes in the rat bladder 2 and 4 weeks after the induction of AUR. The same parameters were also measured in non-AUR rats (control group). The rat bladder weight in the AUR group at 2 weeks was significantly larger than that of the controls, and returned to the control level 4 weeks after the AUR episode. The voiding behavior studies showed significant increase in micturition frequency per day and decrease in single voiding volume 3 days after the induction of AUR, and this voiding behavior was continued for more than 2 weeks. The cystometric studies showed a significant decrease in single-voided volume at 2 weeks rat. However, no significant changes of the other parameters were observed in the rats. The histological studies showed significant infiltration of neutrophils and lymphocytes, as well as increase in turnover of epithelium in AUR rats at 2 weeks, while significant increases in fibrosis in submucosal layer were observed in AUR rats at 4 weeks. This study demonstrated that bladder dysfunction in the rat model caused by AUR needs more than 2 weeks of recovery period. The AUR-associated alterations in the bladder may represent a key clue to understand the underlying pathophysiological mechanisms, which take place in OAB syndrome.