Elastic properties in the circumferential direction in isolated rat small intestine

The aim was to study the passive biomechanical wall properties in the isolated duodenum, jejunum and ileum of the rat. The organ bath contained a Krebs-Ringer solution with 10(-2) M MgCl2 to abolish smooth muscle contractile activity. Stepwise inflation of an intraluminal balloon, in which the cross-sectional area (CSA) was measured, provided the distension stimulus. The circumferential wall stress-strain distributions were computed from steady-state values of these measurements and the unstressed wall thickness was measured in order to evaluate the passive elastic properties. The CSAs measured increased from duodenum to jejunum and to ileum (P < 0.001). At the highest applied pressure load the CSA was 16.64 +/- 0.46 mm2 for the duodenum, 18.70 +/- 0.53 mm2 for the jejunum and 21.73 +/- 0.49 mm2 for the ileum. The wall thickness was 0.19 +/- 0.01, 0.25 +/- 0.01 and 0.28 +/- 0.02 mm, in duodenum, jejunum and ileum, respectively (P < 0.01). All segments showed stress-strain distributions that were exponential by nature. Applying the function Y = exp (a + bX) gave a median determination coefficient of 0.98 (quartiles 0.96-0.99). The duodenum was significantly stiffer than the two other segments. The values of a and b were 2.03 +/- 0.11 and 14.82 +/- 1.81, 1.39 +/- 0.20 and 13.15 +/- 1.42, and 1.13 +/- 0.13 and 10.69 +/- 0.65 for the duodenum, jejunum and ileum, respectively. The a differed between the duodenum and the other segments (P < 0.001). whereas the b differed only between the duodenum and ileum (P < 0.005). In conclusion, differences in the luminal CSA, wall thickness and elastic properties were found between the duodenum, jejunum and ileum.