Myoelectric activity and intraluminal pressure of the canine ileocolonic sphincter.

We constructed ileocolonic loops of distal ileum, ileocolonic sphincter, and proximal colon in 5 dogs; neuromuscular continuity was maintained between loop and intact bowel by a bridge of tunica muscularis. To study ileocolonic sphincter function, we recorded myoelectric activity from subserosal electrodes and intraluminal pressures from perfused catheters and a sleeve sensor. Recordings included at least one interdigestive myoelectric complex and four postprandial hours. Ileal slow waves were recorded from the loop and the ileocolonic sphincter; most interdigestive myoelectric complexes were propagated to the ileocolonic sphincter. Intraluminal pressures at the ileocolonic sphincter fluctuated phasically (mean 12.5 cycles/min) for 72% of recording time during fasting and 81% postprandially. Tonic pressures at the ileocolonic sphincter were higher during fasting (31 +/- 18 cmH2O; p less than 0.05) than postprandially (24 +/- 20 cmH2O); moreover, tonic pressures fluctuated more during fasting than after food. Tonic elevations of pressure were prolonged (mean duration 28.5 min) concomitant with arrival of phase 3 of interdigestive myoelectric complexes at the ileocolonic sphincter. Thus the ileocolonic sphincter participates in both the myoelectric and motor components of the interdigestive cycle and exhibits an intense phasic and tonic response to phase 3. The association of tonic pressure and intense phasic contractions may serve to retard and segment ileal chyme. On the other hand, the presence of rapidly propagated phasic pressures in the region may provide the basis for propulsive function. In this way, these unique motor events will facilitate two distinct functions of the region, namely the alternate retarding and forward propulsion of chyme.