Shafik Ahmed, Shafik Ismail, El-Sibai Olfat
Surgery and Experimental Research, Faculty of Medicine, Cairo University, Cairo, Egypt.
Acta Obstet Gynecol Scand. 2005 Mar;84(3):225-9. doi: 10.1111/j.0001-6349.2005.00688.x.
Sexual stimulation produces not only reflex changes in the female external and internal reproductive organs but also extragenital reactions. A mention of the response of the anal sphincters and the rectum to penile thrusting could not be traced in the literature. We investigated the hypothesis that the anal sphincters and the rectum respond to penile thrusting in a way that prevents gas and fecal leakage during sexual intercourse.
The response of the external anal sphincter (EAS) and the internal anal sphincter (IAS) and the rectum to vaginal balloon (condom) distension was recorded in 23 healthy women (age: 33.7 +/- 7.3 years). The vaginal condom was inflated with air in increments of 50-300 ml, and the electromyographic (EMG) activity of the EAS and the IAS, as well as rectal pressure, was recorded. The test was repeated after separate anesthetization of the vagina, the rectum, the EAS and the IAS and after the use of normal saline instead of lidocaine.
Vaginal distension reduced the rectal pressure in the ratio of expansion of the vaginal volume up to a certain volume, beyond which the rectal pressure ceased to decline when more distending volume was added. Similarly, the internal sphincter EMG activity increased progressively on incremental vaginal distension increase until the 150-ml distension was reached after which more vaginal distension caused no further increase of the EMG activity; external sphincter EMG activity showed no response. Vaginal distension, while the vagina, the rectum, the EAS, and the IAS had been separately anesthetized, produced no significant change, but saline did.
Vaginal balloon distension appears to effect rectal wall relaxation and increase of the internal sphincter tone. This seems to provide a mechanism to avoid rectal contents leakage during coitus. Rectal and internal sphincter response to vaginal distension is suggested to be mediated through a reflex we term 'vagino-anorectal reflex', which seems to be evoked by vaginal distension during penile thrusting. The reflex may prove of diagnostic significance in sexual disorders; further studies are needed in order to investigate this point.
性刺激不仅会引起女性内外生殖器官的反射性变化，还会引发生殖器外的反应。在文献中未发现有关肛门括约肌和直肠对阴茎插入反应的相关描述。我们研究了这样一种假设，即肛门括约肌和直肠对阴茎插入的反应方式能够防止性交过程中气体和粪便泄漏。
记录了23名健康女性（年龄：33.7±7.3岁）的肛门外括约肌（EAS）、肛门内括约肌（IAS）和直肠对阴道球囊（避孕套）扩张的反应。阴道避孕套以50 - 300毫升的增量充气，并记录EAS和IAS的肌电图（EMG）活动以及直肠压力。在分别对阴道、直肠、EAS和IAS进行麻醉后以及使用生理盐水代替利多卡因后重复该测试。
阴道扩张会使直肠压力随着阴道容积的增加而降低，直至达到一定容积，超过该容积后，当增加更多扩张容积时，直肠压力不再下降。同样，随着阴道扩张增量增加，内括约肌EMG活动逐渐增加，直到达到150毫升扩张量，之后更多的阴道扩张不会导致EMG活动进一步增加；外括约肌EMG活动无反应。在分别麻醉阴道、直肠、EAS和IAS后，阴道扩张未产生显著变化，但生理盐水则有变化。
阴道球囊扩张似乎会导致直肠壁松弛并增加内括约肌张力。这似乎提供了一种机制，以避免性交过程中直肠内容物泄漏。直肠和内括约肌对阴道扩张的反应被认为是通过一种我们称为“阴道 - 肛门直肠反射”的反射介导的，这种反射似乎是由阴茎插入时的阴道扩张所诱发的。该反射可能在性功能障碍的诊断中具有重要意义；为了研究这一点，还需要进一步的研究。
