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The role of bladder-to-urethral reflexes in urinary continence mechanisms in rats

Departments of ¹Urology and ³Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213; and ²Pharmaceutical Research Division, Takeda Chemical Industries, Osaka 532-8686, Japan

Submitted 5 February 2004 ; accepted in final form 23 April 2004

Urethral closure mechanisms during passive increments in intravesicular pressure (P_ves) were investigated using microtip transducer catheters in urethane-anesthetized female rats. After a block of reflex bladder contractions by spinal cord transection at T8-T9, abruptly raising P_ves to 20, 40, or 60 cmH₂O for 2 min induced a bladder pressure-dependent contractile response in a restricted portion of the middle urethra (12.5–15 mm from the urethral orifice) that was abolished by cutting the pelvic nerves bilaterally. In pelvic nerve-intact rats, the bilateral transection of either the pudendal nerves, the nerves to the iliococcygeous/pubococcygeous muscles, or the hypogastric nerves significantly reduced (49–74%) the urethral reflex response induced by passive P_ves increases, and combined transection of these three sets of nerves totally abolished the urethra-closing responses. In spinal cord-intact rats, similar urethral contractile responses were elicited during P_ves elevation (20 or 40 cmH₂O) and were also eliminated by bilateral pelvic nerve transection. After spinal cord and pelvic nerve transection, leak point pressures, defined as the pressure inducing fluid leakage from the urethral orifice during passive P_ves elevation by either bladder pressure clamping in 2.5-cmH₂O steps or direct compression of the bladder, were significantly lowered by 30–35% compared with sham-operated (spinal cord-transected and pelvic nerve-intact) rats. These results indicate that 1) passive elevation of P_ves can elicit pelvic afferent nerve-mediated contractile reflexes in the restricted portion of the urethra mediated by activation of sympathetic and somatic nerves and 2) bladder-to-urethral reflexes induced by passive P_ves elevation significantly contribute to the prevention of stress urinary incontinence.

stress urinary incontinence; urethral resistance; leak point pressure

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