Electric pacing of intact and transected canine small intestine and its computer model.

In 10 conscious, fasted dogs with electrodes chronically implanted on the intestine, current pulses (8 mA, 50 ms) at frequencies the same as, or faster than, that of the natural intestinal pacemaker always entrained pacesetter potentials (PP) along the proximal frequency plateau, but not along the distal frequency gradient. As duodenal PP's were paced faster, the proximal plateau shortened by orad extension of the distal gradient. Entrained PP's propagated orally and aborally. Their velocity slowed caudally while varying inversely with their frequency. After midduodenal transection had reduced the frequency of the natural PP's distal to the cut, pacing entrained PP's in all areas of the bowel and restored the proximal plateau and distal gradient. But no area could be paced faster than before transection. PP's were not propagated across sites of transection. A digital computer model of coupled relaxation oscillators gave similar results. We conclude that the frequency of the natural pacemaker and the declining gradient of maximal driven frequency determine the frequency pattern of the small intestinal PP.