Colonic motility and transit of digesta during hard and soft faeces formation in rabbits.

Abstract

SUMMARY1. Rabbits produce hard and soft faeces in a circadian rhythm. This study was undertaken in order to examine the motor function of the colon in relation to the formation of these two types of faeces.2. Colonic motility was measured in unanaesthetized rabbits using strain-gauge transducers and simultaneous radiography.3. Three types of contractions were found in the rabbit proximal colon: haustral activity, segmental activity, and mass peristalsis. Distinctly different motor patterns were observed during the formation of hard and soft faeces.4. When hard faeces were produced, the motor activity of the proximal colon was enhanced. It consisted ofsegmental and haustral activity. The segmental contractions separated the digesta into faecal pellets and forced them slowly aborad, whereas the movements of the haustra carried the liquid contents back towards the caecum.5. When soft faeces were produced haustral and segmental activity was reduced and transfer of the digesta through the proximal colon was accelerated by mass movements.6. In contrast to the proximal colon, the motility of the distal colon was enhanced during the formation of soft faeces and decreased during the production ofhard faeces.7. The results support the concept that hard faeces are chiefly produced by a separation of liquids and solids and by a retrograde transfer of liquid digesta rather than by an increased absorption of water.

Neurogenic and myogenic motor patterns of rabbit proximal, mid, and distal colon

“…It is likely that different conditions of the luminal content (e.g., greater volume or viscosity) would generate neurally dependent movements on the oral side of the transition zone (28). The CMMCs in this study were found to propagate all the way along the single tenia region of the proximal colon to the colonic flexure (fusus coli) at a remarkably constant velocity, similar to those reported previously as "haustral progression" at 0.1 mm/s (28) and as "segmental contractions" at 0.1-0.3 mm/s (16,17). The characteristics of CMMCs in rabbit colon were similar to those described in other species (6,13,36,37,40).…”

“…Ehrlein described in vivo myogenic contractions with mainly retrograde propagation, which he called "haustral activity with rolling movements" (16). As Ehrlein suggested (16), it seems likely that myogenic ripples are primarily involved in mixing rather than propulsion of content.…”

“…Previous studies have investigated the motility in the rabbit proximal colon, both in vitro and in vivo (16,17,28,35). Other studies of isolated segments of rabbit distal colon described neural mechanisms involved in excretion of the fecal pellets (3,6,10,26).…”

“…In the rabbit colon, four distinct colonic regions have been described (2,16,17,35,39). The first three regions form the proximal colon, and the fourth region comprises the distal colon.…”

“…These movements are due to coordinated contractions and relaxations of the internal circular smooth muscle layer and the external longitudinal smooth muscle. These smooth muscle layers are controlled by both myogenic mechanisms [initiated by interstitial cells of Cajal (ICCs)] and neurogenic mechanisms (via the enteric nervous system), which interact to generate diverse motor patterns (21, 31).In the rabbit colon, four distinct colonic regions have been described (2,16,17,35,39). The first three regions form the proximal colon, and the fourth region comprises the distal colon.…”