Effect of warming on the rectal motile activity: identification of rectal warming reflex

The identification in the rectal wall of warm receptors sensitive to warm temperature has not been found in the literature. Therefore, we investigated the hypothesis that rectal warming effects rectal dilation, which seems to indicate the existence of warm receptors.

The rectal wall tone was studied in 24 healthy volunteers (14 men, 10 women, mean age 36.7+/-10.4 years). It was assessed by a barostat system during rectal infusion with normal saline at 30 degrees C, 40 degrees C, 45 degrees C, and 50 degrees C. The test was repeated after rectal anesthetization with lidocaine.

The rectal tone on rectal saline infusion at a temperature of 30 degrees C showed no response (P>0.05), whereas at a temperature of 40 degrees C, 45 degrees C, and 50 degrees C, it exhibited a significant decrease (P<0.05, <0.01, <0.001, respectively), which was proportional to the rising degree of temperature. Warm saline infusion into the anesthetized rectum resulted in no significant change in the rectal wall tone.

Rectal infusion with warm saline produced rectal dilation that increased with temperature elevation. This effect is suggested to be mediated through a reflex called "rectal warming reflex: and advances the possibility of the existence of warm receptors in the rectal wall; however, further studies are needed to confirm the issue.