PRESERVATION OF PERISTALTIC REFLEX IN HYPERTROPHIED ILEUM OF GUINEA-PIG

Chronic obstruction of the guinea pig ileum leads to distension and mu scular hypertrophy, but how this affects passive biomechanical and ner ve-mediated contractions and clearance known as peristaltic reflex is unclear. Ileum of controls had a diameter of 3.0 +/- 1.1 mm and a circ ular muscle thickness of 37.2 +/- 11.2 mu m; 4 wk after placement of a nonconstricting Gore-Tex band, the ileum was distended to 10.0 +/- 0. 19 mm, and its muscle had hypertrophied to 195.0 +/- 61.2 mu m. Hypert rophied segments exceeded controls in capacity (e.g., 5.1 +/- 1.1 vs. 1.1 +/- 0.2 ml at 6 cm); compliance, and hysteresis. Threshold volumes and pressures that triggered the reflex were 3.3 +/- 1.3 ml and 3.1 0 .01 mmHg in hypertrophied vs. 0.7 +/- 0.2 ml and 1.5 +/- 0.2 mmHg in c ontrols. The diameter increase that triggered the reflex was 1.4 +/- 0 .1 mm in hypertrophied segments and 0.6 +/- 0.1 mm in controls. Hypert rophied segments generated fewer contractions of virtually double the amplitude and failed to generate a pressure differential between up- a nd downstream sites as controls did. Hypertrophied segments generated larger stroke volumes and cumulative clearance than controls. The rati o of antegrade to retrograde clearance was similar in hypertrophied an d control segments. The length of the occluding segment in hypertrophi ed preparations exceeded that of controls. Control contractions indent ed the antimesenteric border and propagated antegrade from their site of origin; bizarre writhing movements of hypertrophied segments made t heir contractions difficult to monitor. Thus distension and muscular h ypertrophy do not interfere with the ability of the chronically obstru cted guinea pig ileum to generate a peristaltic reflex at least as rea dily and as powerful and as effective in clearing the lumen as control s.