Role of the rectosigmoid pacemaker and electric activity in rectal motility: mechanism and clinical significance.
BACKGROUND
The rectum exhibits electric activity in the form of slow waves or pacesetter potentials (PPs) and action potentials (APs), which are suggested to be initiated from a rectosigmoid pacemaker (RSP). We hypothesized that the RSP and electric waves are responsible for rectal motility. This hypothesis was investigated.


METHODS
The rectum of 13 mongrel dogs was exposed through an abdominal incision, and 3 electrodes were fixed serially to the rectal serosa. The rectal pressure was measured by a 6 F saline-perfused catheter and the rectal electromechanical response to rectal balloon distension in increments of 5 ml of air was registered. The test was repeated after rectosigmoid junction (RSJ) anesthetization by 20 minutes and 3 hours using xylocaine injection. It was done also after saline instead of xylocaine injection.


RESULTS
PPs and APs were recorded and had the same frequency, amplitude and conduction velocity from the 3 electrodes of the same animal. APs occurred randomly and were coupled with elevated rectal pressure. Rectal balloon distension produced increase of the rectal electric activity and pressure, which increased with the increase of the rectal distension until, at a mean volume of 31.2 +/- 5.4 ml, the balloon was expelled to the exterior. RSJ anesthetization abolished the rectal electric waves and effected no balloon expulsion with high volume rectal distension. The rectal waves appeared after waning of the anesthetic effect. Saline injection into the RSJ produced no significant effect on the rectal electromechanical activity.


CONCLUSIONS
Rectal electric waves are suggested to be initiated from the RSP and to be responsible for the rectal motor activity. Incremental rectal balloon distension effected progressive increase of the rectal electromechanical activity until the balloon was expelled to the exterior RSJ anesthetization blocked the electric waves and the electromechanical response to rectal distension. These results have probably clinical significance when performing electrorectograms for various rectal pathologic conditions as well as when applying an artificial pacemaker to the non-contractile rectum.
Shafik
Ahmed
A
Department of Surgery and Experimental Research, Faculty of Medicine, Cairo University, Cairo.
Mostafa
Randa M
RM
Ahmed
Ismail
I
el-Sibai
Olfat
O
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001683:Biological Clocks / Q000502:physiology*; D004285:Dogs; D004594:Electrophysiology; D005260:Female; D005769:Gastrointestinal Motility / Q000502:physiology*; D008297:Male; D010138:Pacemaker, Artificial; D010507:Periodicity; D011312:Pressure; D012007:Rectum / Q000502:physiology*