COOPERATIVE ROLES OF COLON AND ANORECTUM DURING SPONTANEOUS DEFECATION IN CONSCIOUS DOGS

Colorectal motility during spontaneous defecation was investigated usi ng force strain gauge transducers implanted in the proximal colon, dis tal colon, rectum, and anus in six dogs. One 24-hr recording and sever al defecation recordings were made in each dog. During 24-hr recording s, 29 giant contractions were observed in the distal colon. The giant contractions, which propagated to the rectum, accompanied evacuation m ore frequently than those that stopped at the distal colon (P < 0.05). Of 66 episodes of defecation, 63 (95%) were accompanied by a giant co ntraction of the distal colon. Of these, 57 (90%) propagated to the re ctum. In three events, giant contraction originated at the rectum. The rectum relaxed prior to the contraction. The internal anal sphincter also relaxed. Migration of giant contraction to the rectum, rectal rel axation-contraction sequence and sphincter relaxation played important roles during defecation. Defecation is a consequence of successive ph enomena occurring in both the colon and anorectum.