[Studies on colonic motor correlates of spontaneous defecation in conscious dogs]

The colonic motilities during defecation were studied by means of extraluminal strain gauge force transducers in six conscious dogs. A set of eight transducers was implanted in each dog: one was on the terminal ileum and the remaining seven were on the whole length of the colon equidistantly. As Karaus & Sarna had already described in 1987, giant migrating contractions (GMC) that were initiated in the proximal colon and rapidly migrated caudad before defecation were reconfirmed also in this study to be motor equivalent of mass movements. Several new findings in addition were obtained. At spontaneous defecation, a reflex relaxation was always observed at the distal end of the colon. This colonic outlet relaxation (COR) usually occurred synchronously with the initiation of GMC at the proximal colon and lasted until GMC had arrived at the distal end. Evacuation of feces occurred during this COR. COR was not observed at defecation induced by neostigmine or prostaglandin F2 alpha. After bilateral pelvic nerve section, both GMC and COR were completely abolished. Instead, group of low amplitude caudad migrating contractions occurred at the proximal or middle colon and were followed by frequent evacuation of small amount of loose stools. COR was not observed at this type of defecation. It is suggested from this study that not only GMC but also COR are the essential motor correlates of spontaneous defecation. Both GMC and COR are under control of pelvic nerves.