DOG-MODEL FOR STUDYING DETRUSOR INSTABILITY SECONDARY TO ACUTELY INDUCED VARIABLE BLADDER OUTLET OBSTRUCTION

BACKGROUND. Involuntary detrusor contractions often cause irritative s ymptoms such as urgency and incontinence. A dog model for acutely indu ced variable bladder outlet resistance was developed to investigate th e possible role of prostatic afferent nerve fibers in the development and maintenance of detrusor instability. METHODS. Fifty-eight mongrel dogs (weight range 19.5-36.5 kg) were divided into five groups: group I (n = 11) had surgically induced bladder outlet obstruction. Group II (n = 14) had urinary obstruction and bilateral sectioning of the lowe st branches of the pelvic plexus supplying the prostate. Group III (n = 10) had prostate denervation only. Groups IV (n = 10) and V (n = 13) were sham-operated and controls, respectively. In the obstructed grou ps (I and II), an artificial urinary sphincter (length 4.5-6.0 cm) was placed around the bladder neck and connected to a reservoir placed su bcutaneously to allow postoperative adjustments of urinary resistance. All dogs were evaluated at baseline and postoperatively at 1, 3, and 6 months with uroflowmetry, postvoid residual urine volume, cystometry as well as serum creatinine, and urinalysis. RESULTS. Occurrences of detrusor instability were not associated with prostatic denervation in put. The mean peak flow rates decreased significantly in the obstructe d groups at all follow-ups, but did not change significantly in the no nobstructed groups. Postoperatively, the mean maximum bladder capacity was significantly decreased for groups I and II only. Ho ct ever, a s ignificant correlation between maximum bladder capacity and maximum de trusor pressure could not be detected at any time point in any of the groups. Mean postvoid residual urine volume varied considerably in all groups over time. Creation of a urinary model of infravesical obstruc tion was associated with considerable problems. CONCLUSIONS. In our do g model of bladder outlet obstruction, prostatic sensory nerve fibers appear not to be involved in detrusor instability. Surgical induction of: a constant model of bladder outlet obstruction was difficult even in a large animal. The observations from the present study raise quest ions about the validity of obstructive urinary animal models. (C) 1998 Wiley-Liss, Inc.