Study of the electrical and mechanical activity of the rectum: an experimental study.

The electrical activity of the rectal detrusor was studied in 13 dogs. 10 electrodes were sutured serially to the rectal and lower sigmoid colon serosa. Electrical activity was recorded for 30 min/day for 10 days. Simultaneous electric and mechanical activity (recorded by a 6-French catheter connected to a pressure transducer) was also recorded with and without rectal distension by a condom balloon. Electrical activity was further determined after annular myotomy performed at different levels in the rectum and lower sigmoid colon. Pacesetter potentials (PP) were recorded from electrodes 3-10. They were triphasic, propagated caudally and had the same frequency and regular rhythm by all electrodes distal to the 3rd one. Frequency was constant in each dog from day to day. PP were accompanied by action potentials (AP) which had inconsistent frequencies and were accompanied by increased rectal pressure. Rectal distension led to an increase in both the frequency and amplitude of PP and AP. Rectal myotomy below the 3rd electrode resulted in PP and AP disappearing distal but not proximal to the cut, excluding the 1st and 2nd electrodes, which did not show activity. The results suggest that PP start at the 3rd electrode, which corresponds anatomically to the rectosigmoid junction (RSJ). AP cause contractile activity along the rectum. It seems that the RSJ is the site of a pacemaker triggering the PP that pace the AP which initiate the rectal contractile activity.