Differential sensitivities of morphine and motilin to initiate migrating motor complex in isolated intestinal segments: regeneration of intrinsic nerves

The effect of morphine and motilin on surgically isolated segments of small intestine was studied in 8 dogs. In 4 dogs, the small intestine was divided into four segments by simple transection and reanastomosis (group 1); in 4 others, a 2-4-cm colonic segment was interposed at each of the transection sites (group 2). The migrating motor complex initially cycled independently in each segment in group 1 dogs; after that the migration of the migrating motor complex across transection and reanastomosis began to recover and the recovery was complete 100 days after surgery. In contrast, in group 2 dogs the migration of the migrating motor complex from one segment to the next did not recover even 180 days after surgery. Morphine bolus or infusion initiated premature phase III activity in all segments but the sensitivity to morphine decreased distally. Motilin bolus or infusion initiated premature phase III activity only in the first three segments. The sensitivity to motilin also decreased distally. We concluded that (a) the interposition of a foreign segment severely impedes or prevents the regeneration of enteric nerves; (b) the sensitivity of morphine and motilin in initiating premature phase III activity decreases distally in small intestine; and (c) motilin does not initiate premature phase III activity in the ileum, but morphine may initiate premature phase III activity at all sites in the small intestine.