Electric activity of the rectosigmoid canal and its relation to rectal and sigmoid electric activity: an evidence of a sphincteric function of the rectosigmoid canal.

We have previously demonstrated that the rectosigmoid junction is more than a junction: it is a segment with a mean length of 2.8 cm which we termed the 'rectosigmoid canal' (RSC). Our data support the existence of a physiologic and anatomic sphincter at the RSC which regulates the passage of stools from the sigmoid colon (SC) to the rectum (R). In view of its sphincteric action we investigated the hypothesis that the RSC has a higher electric activity than that of the SC and R. The tests were performed during repair of huge incisional hernia in 11 subjects (age 46.7(12.5 years; 8 women). The electric activity was recorded by means of 2 monopolar electrodes applied to each of the SC, RSC and R. The RSC was then anesthetized with xylocaine and the electric activity of SC, RSC and R was recorded after 10 minutes and one hour. The test was repeated using saline instead of xylocaine. The SC, RSC and R exhibited electric activity in the form of pacesetter potentials (PPs) and action potentials (APs). The PPs were monophasic in the SC and triphasic in the RSC and R. The frequency, amplitude and conduction velocity of the waves recorded from the RSC and R had higher readings (p<0.05) than those from the SC. The RSC and R showed a similar frequency and conduction velocity, but the RSC had a higher amplitude (p<0.05). Ten minutes after RSC anesthetization, electric waves were recorded from the SC but not from the RSC or R; electric activity returned one hour after anesthetization. Saline injection of the RSC did not affect the electric activity of the RSC, SC or R. The electric wave pattern and parameters of the RSC and R differed from those of the SC, suggesting that they are evoked by 2 different pacemakers. The similarity in pattern, frequency and conduction velocity of electric waves of RSC and R supposedly denotes that the rectal waves are a continuation of those of the RSC and that both are evoked by a single pacemaker located in the RSC. The higher amplitude of the RSC waves may be due to the thicker RSC musculosa in comparison to that of the SC and R and may by itself be an evidence of the sphincteric function of the RSC.