Intrinsic differences in the filling response of the guinea pig duodenum and ileum

Transit of intestinal contents differs between the duodenum and ileum in intact animals. To determine whether this relates to intrinsic differences in the capacity, distensibility, or filling response of these segments, we used the isolated duodenum and ileum of 13 guinea pigs to record: (1) increases in the diameter and luminal volume produced by specific pressure heads and (2) the pressure waves and movements of the segments in response to bolus injections. We found that the duodenum and the ileum had similar diameters in the empty state, and when filled with volumes below 0.4 ml both generated baseline pressures below 3 cm H2O. However, the ileum increased its diameter and volume significantly more in response to increases in inflow pressure than the duodenum did. Conversely, injection of bolus volumes led to pressure waves of higher amplitude and longer duration in the duodenum than in the ileum. The pressure waves were produced by sharply defined ring contractions in the ileum; there was bulging of the walls downstream from the contraction site and collapse upstream from it. In the duodenum, the contraction involved a longer segment and was shallow with ill-defined margins. These intrinsic differences in the capacity, distensibility, and contraction patterns of the duodenum and ileum are likely to affect luminal transit and other mechanical functions of these intestinal segments in the intact animal.