A study of the effect of distension of the rectosigmoid junction on the rectum and anal canal with evidence of a rectosigmoid-rectal reflex.

PURPOSE

To elucidate the role of the rectosigmoid junction (RSJ) in the mechanism of defecation.

METHOD

Fourteen healthy volunteers were enrolled in the study (10 men, 4 women; mean age 38.2 +/- 10.6 years). The pressures in the rectum, anal canal, and RSJ as well as rectal balloon expulsion were recorded in response to balloon distension of the RSJ in increments of 10 ml of carbon dioxide (CO2) to 50 ml. The experiments were repeated after individual anesthetization of the RSJ, rectum, and anal canal. The expulsion of a 50-ml distended balloon located in the anesthetized rectum was tested.

RESULTS

RSJ distension with 10 ml of CO2 produced no significant pressure changes in the RSJ, rectum, or anal canal. A 20-ml distension effected a significant pressure rise in the RSJ (P < 0.05) and the rectum (P < 0.01) and a decline in the anal canal (P < 0.05); the rectal balloon was expelled to the exterior. Similar pressure changes (P > 0.05) were recorded with a 30-, 40-, and 50-ml balloon distension. The mean latency for the RSJ response was 12.6 +/- 2.2 ms and for the rectum 15.8 +/- 2.6 ms. The balloon, distended with 50 ml of CO2 and located in the rectum, was not expelled to the exterior. Balloon expulsion occurred only with distension with volumes of above 80 ml. Individual anesthetization of the RSJ, rectum, and anal canal followed by RSJ distension produced no significant pressure changes in RSJ, rectum, and anal canal as well as no rectal balloon expulsion.

CONCLUSION

The rectal contraction upon RSJ distension affirms the hypothesis of the possible involvement of a reflex, which we term "rectosigmoid-rectal reflex." This reflex relationship is evidenced by reproducibility and its absence on anesthetization of either the RSJ or the rectum, both presumably representing the two arms of the reflex arc. It is postulated that stools passing from the sigmoid colon to the rectum distend the RSJ and evoke the rectosigmoid-rectal reflex, which produces rectal contraction. The role of the reflex in defecation disorders needs to be studied.