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 c olon serosa. Electrical activity was recorded for 30 min/day for 10 da ys. Simultaneous electric and mechanical activity (recorded by a 6-Fre nch catheter connected to a pressure transducer) was also recorded wit h and without rectal distension by a condom balloon. Electrical activi ty 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, propagate d caudally and had the same frequency and regular rhythm by all electr odes distal to the 3rd one. Frequency was constant in each dog from da y to day. PP were accompanied by action potentials (AP) which had inco nsistent frequencies and were accompanied by increased rectal pressure . Rectal distension led to an increase in both the frequency and ampli tude of PP and AP. Rectal myotomy below the 3rd electrode resulted in PP and AP disappearing distal but not proximal to the cut, excluding t he 1st and 2nd electrodes, which did not show activity. The results su ggest that PP start at the 3rd electrode, which corresponds anatomical ly to the rectosigmoid junction (RSJ). AP cause contractile activity a long the rectum. It seems that the RSJ is the site of a pacemaker trig gering the PP that pace the AP which initiate the rectal contractile a ctivity.