Urethral pressure changes in reflex micturition

The mechanism and pattern of urethral pressure changes during bladder filling and voiding were investigated in anesthetized female dogs. A series of experiments was performed involving simultaneous recording of intraurethral and intravesical pressures before and after surgical separation of the bladder from the urethra. Similar experiments were done after pharmacologic blockade of the striated muscles, alpha-adrenergic receptors, and autonomic ganglia. The urethral pressure rise during the collection phase and its drop simultaneous with bladder contraction were observed both before and after vesicourethral interruption. Tubocurarine did not block pressure changes recorded in the proximal urethra. Phentolamine did not prevent a urethral pressure drop simultaneous with detrusor contraction. After effective blockade of autonomic ganglia by pentolinium, reflex micturition could not be induced by bladder filling. However subsequent administration of bethanechol chloride induced a bladder pressure rise together with a simultaneous drop of urethral pressure. We conclude that both vesicourethral muscle continuity and autonomic reflexes contribute to the urethral pressure changes during the two phases of bladder activity, passive collection and active expulsion.