Effect of urethral dilation on vesical motor activity: identification of the urethrovesical reflex and its role in voiding

PURPOSE: We investigated the hypothesis that mild urethral distention, which presumably occurs during the passage of urine through the urethra, stimulates stretch receptors in the urethral wall, leading reflexively to vesical contraction. MATERIALS AND METHODS: We evaluated 9 male and 10 female healthy volunteers with a mean age +/- SD of 39.6 +/- 8.3 years. The posterior urethra was distended by a balloon filled with saline in 1 ml. increments up to 6 ml., while recording vesical pressure. The test was repeated after individual anesthetization of the urethra and bladder. RESULTS: Vesical pressure increased significantly at 1 and 2 ml. urethral distention (p <0.01). Increases in urethral distention effected further vesical pressure elevation (p <0.001), although there was no significant difference in distention at 3 to 6 ml. (p >0.05). No significant vesical pressure response of the individually anesthetized urethra or bladder occurred during urethral distention. CONCLUSIONS: Urethral distention is thought to cause vesical contraction through the stimulation of urethral stretch receptors. Vesical contraction at urethral distention postulates a reflex relationship that was abolished by individual anesthetization of the urethra and bladder. This relationship, which we call the urethrovesical reflex, appears to have a role in maintaining vesical contraction during voiding. Further studies are required to investigate the role of this reflex in voiding disorders.