The effect of simulated birth trauma and/or ovariectomy on rodent continence mechanism. Part I: functional and structural change.

PURPOSE: We examined the changes in the lower urinary tract after delivery, intravaginal ballooning and/or ovariectomy.

MATERIALS AND METHODS: The study included 10 virgin and 48 primiparous pregnant rats. Cystometry and the stress/sneeze test were performed in virgin and postpartum rats shortly after delivery and at 8 weeks before sacrifice. Half of the delivered animals underwent intravaginal balloon dilation. Four weeks later half in each group underwent ovariectomy. The rats were subdivided into group 1--delivery, group 2--delivery plus balloon inflation, group 3--delivery plus ovariectomy and group 4--delivery plus balloon inflation plus ovariectomy. Tissues from the bladder, bladder neck, urethra and levator were collected, analyzed by electron microscopy, and immunostained for caveolin-1, caveolin-3 and neuronal nitric oxide synthase.

RESULTS: Higher bladder capacity was detected in postpartum than in virgin rats. Urine leakage on stress/sneeze testing increased significantly in groups 2 and 4. Electron microscopy revealed a significant decrease in sarcolemma caveolae in the smooth muscle of the bladder and urethra in groups 2 to 4. In the bladder neck in group 3 caveolae were increased in smooth muscle. In groups 2 to 4 in the smooth muscle of the bladder and urethra caveolin-1 was significantly decreased. Caveolin-3 and neuronal nitric oxide synthase in striated muscle also significantly decreased in groups 2 to 4.

CONCLUSIONS: These findings suggest that birth trauma simulated by ballooning and ovariectomy may contribute to stress urinary incontinence. The alteration in smooth muscle caveolae as well as the membrane protein caveolin may have a role in functional alterations caused by birth trauma and ovariectomy.