PURPOSE: To our knowledge the physiological mechanisms involved in sexual intercourse have not been completely explored. We hypothesized that vaginal distention induced by penile thrusting may affect the function of the bladder and urethra. To verify this supposition we assessed the effect of vaginal distention on vesical and urethral pressure. No relevant reports in the literature were identified. MATERIALS AND METHODS: The response of vesical and urethral pressure to vaginal distention was recorded in 26 healthy women volunteers with a mean age plus or minus standard deviation of 36.7 +/- 9.8 years. A condom was introduced into the vagina and inflated with carbon dioxide in increments of 10 ml. up to 80 ml. Vesical and urethral pressure was measured by a 2-channel microtip catheter connected to a transducer. The vesicourethral pressure response to vaginal distention was also tested after individual anesthetization of the bladder, urethra and vagina. RESULTS: No vesicourethral pressure response was recorded with 10 and 20 ml. of vaginal distention. At 30 and up to 80 ml. of distention bladder pressure decreased and urethral pressure increased (p <0.05). There was no significant difference when the volume of vaginal distention was increased. Mean duration of the pressure response was 4.2 +/- 0.6 seconds. Pressure returned to normal after a latency period of 5.2 +/- 1.1 seconds, although the vagina was continuously distended. Vaginal distention during anesthetization of the bladder, urethra or vagina did not evoke a pressure response. CONCLUSIONS: The vesicourethral response to the inserted condom, which by inflation adopts the shape of the erect penis, seems to simulate the response of the vagina when it is distended by the erect penis during coitus. The constant vesicourethral pressure response to vaginal distention postulates a reflex relation, which we call the vagino-vesicourethral reflex. This reflex is apparently evoked during coitus, leading to momentary vesical dilatation and increased urethral sphincter activity, which most likely acts to prevent urinary leakage during coitus. Reflex disorders may explain urinary leakage during coitus in some neuropathic conditions.
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