Distinctive patterns of interdigestive motility at the canine ileocolonic junction

Studies of interdigestive motor activity in the distal ileum, ileocolonic sphincter, and proximal colon were performed in two groups of dogs: (i) in those with ileocolonic loops that maintained neuromuscular continuity with the proximal intestine, we used an intraluminal side-hole assembly; (ii) in those with intact bowel, we attached extraluminal strain gauge transducers. Both groups of animals were equipped also with serosal electrodes. Positioning of motor sensors could be defined accurately by (a) a clear separation of rhythmic frequencies between those of the distal ileum (mean 10.8 cycles/min) and proximal colon (mean 6.2 cycles/min) and (b) the characteristic motor patterns of the ileocolonic sphincter. Analysis of motor activity in the segment demonstrated four distinct patterns: (i) irregular, apparently random phasic waves, (ii) rhythmic bursts of contractions corresponding to phase III of the migrating motor complex, (iii) other slowly propagated bursts of rhythmic activity (mean duration 3.6 min) recurring on average every 10 min, and (iv) single, prolonged (mean duration 16.7 s), high amplitude (mean 271 cmH₂O) waves that propagated rapidly ("prolonged propagated contractions"). The latter two patterns appear unique to, or unusually prominent in, this region. A high degree of motor coordination between the distal ileum, ileocolonic sphincter, and proximal colon was also recognized. Thus, the patterns of motor activity suggest a specialized function for the distal 30 cm of ileum, the ileocolonic sphincter, and the proximal colon. These unique and coordinated patterns of motility deserve further exploration, especially in relation to ileocolonic transit and actions of the sphincter as a barrier to colo-ileal reflux.