Study of the effect of temperature on the rectal function with evidence of thermorectal reflex

Rectal sensation seems to originate from mechanoreceptors which are stimulated by passive rectal filling or active contraction. We investigated the effect of temperature on rectal function.

A balloon was introduced into the rectum of 28 healthy volunteers, filled with 50 ml saline at various temperatures, and rectal pressure was recorded. The test was repeated 30 min and 3 h after rectal anesthetization.

Rectal pressure was significantly reduced at 45 degrees and 40 degrees C, showed no change at 37 degrees or 30 degrees C, and was increased at 20 degrees, 10 degrees, and 0 degrees C. At 45 degrees C patients felt rectal pain but no sensation of warmth; at 40 degrees, 37 degrees, and 30 degrees C neither rectal pain nor warm sensation was felt; at 20 degrees C or below rectal pain and cold sensation were perceived. Rectal balloon filling 30 min after anesthetization caused no significant rectal pressure changes or sensation of coldness or warmth; after 3 h, when the anesthetic had waned, the rectal pressure response and sensation were similar to those before anesthetization.

Warm saline appears to cause rectal relaxation and cold saline rectal contraction. Subjects did not perceive sensation of warmth in the rectum but felt cold sensation, which may indicate the presence of cold receptors in the rectal wall. The rectal response to temperature variations is suggested to be reflex in nature as evidenced by its absence on rectal anesthetization. Such reflex, designated "thermorectal reflex," is proposed to mediate the rectal response and is speculated to have clinical significance in rectal dysfunctional and neurogenic disorders.