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Use of a rabbit model to investigate the feasibility of using an innervated neosphincter transplant for the treatment of stress urinary incontinence.

Aim:  To examine the feasibility of using an innervated smooth muscle wrap as a neosphincter in a rabbit model of urinary incontinence.Methods:  Rabbits were rendered incontinent surgically by lesion of the proximal urethral wall to the level of the submucosa (n = 20). In twelve animals a strip of dartos smooth muscle was wrapped around the lesioned urethra to create a new urethral sphincter and stimulating electrodes were inserted into the muscle. After a recovery period of at least one‐week cystometrograms were established for control (urethra intact), lesioned and lesion plus neosphincter animals.Results:  Infusion of saline into the bladder of control animals caused a slow rise in bladder pressure until, at approximately 20–30 ml, there was an increase in pressure that rose steeply and was associated with bladder emptying. The threshold for this reflex emptying was 2–3 cm H2O, and the maximum pressure during the reflex was 6–15 cm H2O. After the bladder emptied, the pressure dropped to 0–2 cm H2O. In rabbits with lesioned sphincters, it was not possible to obtain a normal cystometrogram because there was leakage of fluid from the urethral opening before a volume and pressure sufficient to elicit a reflex was achieved. The loss of the majority of fluid often occurred without a significant pressure increase, that is, there was no true emptying reflex. Similar results were observed in animals in which the urethra had been lesioned and implanted with the smooth muscle neosphincter. Prior to electrical stimulation of the neosphincter, with constant current pulses at 2 Hz, substantial leak occurred at 11.4 ± 2.5 ml, whereas during stimulation voiding occurred at 17.8 ± 1.4 ml. At void or emptying, the peak pressure was 6.1 ± 0.1 cm H20 in control, 0.7 ± 0.2 in operated but not stimulated and 3.5 ± 0.6 in the same animals during stimulation. A satisfactory improvement of continence was observed for a period of up to 6½ months postsurgery. At the end of the study, histological examination confirmed the neosphincter to be both healthy and viable.Conclusion:  Smooth muscles of the dartos display contractile properties which make them suitable for use as transplantable sphincters. A smooth muscle neosphincter, controlled by electrical stimulation, can restore continence after urethral damage.