Role of the longitudinal smooth muscle coat in the ileal motile activity: evidence of ileo-ileal inhibitory reflex.
BACKGROUND
All gut movements are claimed to be activated essentially by the concentric contraction of the circular muscle, moving the chyme aborally. The role of the longitudinal smooth muscle of the small intestine in gut motility is poorly understood; this point was investigated in the current study.


METHODS
The abdomens of 14 crossbreed dogs (eight dogs, six bitches) were opened. A segment of the small intestine was distended by a balloon in increments of 2 mL of saline, and the pressure and electrical activity were recorded proximally and distally to the balloon. The gut wall around the balloon was anesthetized and the test was repeated. The longitudinal muscle coat of the small intestine segment was then excised, and the pressure response and electrical activity were recorded on ileal distension.


RESULTS
Two milliliter ileal distension produced pressure decrease (P < 0.05) proximally and distally to the balloon and caused balloon movement. Four, 6 and 8 mL distension effected similar pressure response, while 10 mL showed no response. Electrical waves were recorded from the three electrodes applied to the ileal segment. Upon ileal distension, electrical activity increased over the distended area, with no activity proximally and distally to it. Balloon distension of the anesthetized ileal segment produced no pressure response or electrical activity. After longitudinal myectomy, no electrical activity was recorded at rest or upon ileal distension, and the balloon did not move.


CONCLUSIONS
Ileal distension initiated circular muscle contraction only in the presence of the overlying longitudinal muscle, which appears to transmit the electrical activity to the circular muscle upon ileal distension. Ileal contraction is suggested to initiate ileal hypotonia in the proximal and distal ileal segments mediated through an 'ileo-ileal inhibitory reflex' that leads to aboral progress of the proximally and distally located chyme.
Shafik
Ahmed
A
Department of Surgery and Experimental Research, Faculty of Medicine, Cairo University, Egypt. ashafik@ahmedshafik.org
Shafik
Ali A
AA
Ahmed
Ismail
I
D000818:Animals; D004285:Dogs; D005260:Female; D005769:Gastrointestinal Motility / Q000502:physiology*; D007082:Ileum / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology*; D012018:Reflex / Q000502:physiology*