Diurnal changes in canine colonic motility were investigated by means
of chronically implanted force transducers. A characteristic of the co
lonic motor profile in the fasted state was the occurrence of colonic
motor complexes consisting of tonic contractions superimposed with pha
sic ones. On feeding, motor complexes were immediately induced in the
whole colon and continued to occur at significantly shorter intervals
than those in the fasted state, but the duration and the amplitude of
the colonic motor complexes were not affected by feeding. This increas
ed activity period lasted for 8-16 h after feeding, and 83.3% of the d
efecations were observed in this period. Of the defecations 33% occurr
ed in the first 2 h after feeding (P < 0.05). More than 80% of the gia
nt migrating contractions associated with defecation propagated from t
he middle to the distal colon, and the start of faeces evacuation coin
cided with the end of the relaxation period of the distal colon preced
ing the arrival of the giant migrating contractions. More than 90% of
the giant migrating contractions not associated with defecation migrat
ed from the proximal to the middle colon. More than 60% of the colonic
motor complexes migrated in an aboral direction and about 18% of them
in an oral direction. These results suggest that (1) defecations tend
to occur immediately after feeding; (2) the regional distribution of
giant migrating contractions was different between those associated an
d not associated with defecation.