Study of the uterine response to vaginal distension: the 'vagino-uterine reflex'

To study the effect of vaginal distension on the uterus, the uterine pressure was measured in 20 healthy female volunteers (mean age 34.3 +/- 7.8 years; 7 nulli-, 13 multiparous) by means of a manometric tube perfused by a pneumohydraulic system. Vaginal distension was induced by a 12 F condom-ended catheter. The condom was inflated in increments of 10 ml of air. The test was repeated after anesthetizing the vagina and uterus, respectively. The uterine pressure increased upon vaginal distension; it showed more rise as the distension increased (p < 0.01). The response was momentary and the pressure returned to basal values although vaginal distension continued. It disappeared upon sustained or successive inflations of 5-7 times and was restored after a resting period of 3-5 min. There was no uterine pressure response when the vagina or uterus were anesthetized and it returned when the anesthetic effect had worn off. No significant difference was found in the pressure response between nulli- and multiparous women (p > 0.05). The aforementioned results were reproducible when repeated in the same woman with no significant difference (p > 0.05). The inflated condom looks like the erect penis, and the uterine response to the inflated condom seems to simulate that of the erect penis distending the vagina during coitus. The constant rise of uterine pressure to vaginal distension postulates a reflex relation which we call 'vagino-uterine' reflex. Uterine contractions during coitus are suggested to have a 'suction-pumping' action on the semen deposited in the vaginal fornices.