Comparison of colonic and ileal propulsive capabilities under conditions requiring hydrostatic work

The intrinsic ability of cat colonic segments to do hydrostatic work to expel fluid was investigated in vitro and compared with the propulsive ability of ileal segments evaluated under identical conditions. Colonic segments spontaneously produced propulsive complexes at an average interval of 4.8 min when basal intraluminal pressure was set at 5 cmH2O. These complexes produced a net ejection of fluid in the aboral direction. When the capacitance of the evaluation system was set at 0.025 ml/cmH2O, colonic segments ejected only 5% of their content. This percentage increased to 23% when evaluation capacitance was increased to 0.125 ml/cmH2O. Peak aboral pressure associated with these complexes was approximately 37 cmH2O at both capacitances. Ileal segments aborally ejected almost twice as much fluid (44% of their luminal content) as did colonic segments at a capacitance of 0.025 ml/cmH2O even though ileal luminal content was five times less than colonic content. The aborally ejected volume per complex did not change when ileal segments were evaluated at two different capacitances even though higher pressures were required to eject fluid at the lower capacitance than at the higher capacitance. These results indicate that the propulsive behavior of ileal and colonic segments has some qualitative aspects that are similar but that only the propulsive ability of colonic segments is pressure limited under the conditions tested. Possible mechanisms that might produce this limitation are considered.