Two Kinds of Urinary Continence Reflexes during Abrupt Elevation of Intravesical Pressure in Rats

Urethral closure mechanisms during abrupt elevation of intravesical pressure (P-ves) were investigated. Middle urethral contractile responses were observed during sneezing and passive P-ves rise for 120 sec. Both responses were decreased when somatic nerves innervating the external urethral sphincter and the pelvic floor muscles were transected. In contrast, while transection of both pelvic and hypogastric nerves had no effect during sneezing, urethral responses during passive P-ves rise were totally abolished or partially reduced after transection of pelvic or hypogastric nerves, respectively. Electrical stimulation of the abdominal muscles for 1 sec elevated P-ves, and P-ves inducing fluid leakage from the urethral orifice was lowered after somatic or pelvic nerves were cut, while hypogastric nerve transection showed smaller effects. These results indicate that at least two kinds of urinary continence reflexes close the middle urethra; one is preprogrammed to close irrespective of bladder afferent activity, the other is triggered by bladder afferent activity. During momentary stress events lasting within 1 sec, the striated muscle mainly contributes to urethral closure, while during events lasting a relatively long period, like passive P-ves rise for 120 sec, both striated and smooth muscles are related to the prevention of urinary incontinence.