Biomechanical remodelling of obstructed guinea pig jejunum

Abstract

Data on morphological and biomechanical remodelling are needed to understand the mechanisms behind intestinal obstruction. The effect of partial obstruction on mechanical properties with reference to the zero-stress state and on the histomorphological properties of the guinea pig small intestine was determined in this study. Partial obstruction and sham operation were surgically created in mid-jejunum of guinea pigs. The animals survived 2, 4, 7, and 14 days. The age-matched guinea pigs that were not operated served as normal controls. The segment proximal to the obstruction site was used for histological analysis, no-load state and zero-stress state data, and distension test. The segment for distension was immersed in an organ bath and inflated to 10cm H(2)O. The outer diameter change during the inflation was monitored using a microscope with CCD camera. Circumferential stresses and strains were computed from the diameter, pressure and the zero-stress state data. The opening angle and absolute value of residual strain decreased (P<0.01 and P<0.001) whereas the wall thickness, wall cross-sectional area, and the wall stiffness increased after 7 days obstruction (P<0.05, P<0.01). Histologically, the muscle and submucosa layers, especially the circumferential muscle layer increased in thickness after obstruction. The opening angle and residual strain mainly depended on the thickness of the muscle layer whereas the wall stiffness mainly depended on the thickness of the submucosa layer. In conclusion, the histomorphological and biomechanical properties of small intestine (referenced for the first time to the zero-stress state) remodel proximal to the obstruction site in a time-dependent manner.

Figure 1

Set-up of experiment. The organ bath is composed of an inside small chamber and an outside chamber. The Krebs solution contained in the small chamber was maintained constant at 37 °C by circulating water in the big chamber using a heating machine. The intestinal segment was placed in the small chamber containing Krebs solution. The volume was applied by a pump and the stretch ratio regulated by a micromanipulator. The pressure probe was used to measure the pressures. The diameter changes of the intestinal segments were videotaped through a stereomicroscope.

Figure 2

The body weight decreased after the operation and reached the lowest point at 3 days for obstruction and 2 days for sham operation.

Figure 3

Mid-jejunal segments obtained from 14 days sham operation (top) and from 14 days obstruction (bottom) guinea pigs. The arrows show the marker for sham operation and ring for obstruction. The intestinal wall was visibly hypertrophied and dilated proximal to the obstruction, whereas no apparent change was observed in the sham-operated animal.

Figure 4

Morphometry data: Compared with the normal and sham operated groups, the wall thickness (Fig. 4A), wall area (Fig. 4B), inner circumference (Fig. 4C) and outer circumference (Fig. 4D) of the intestinal segments at no-load state gradually increased after obstruction. The morphometric data did not differ between normal and sham operation groups.

Figure 5

The layer thickness: The villous height and crypt depth (mucosa thickness) did not differ between the groups (Fig. 5 top), whereas the submucosa and muscle layers increased in a time-dependent manner after obstruction, especially the circumferential muscle layer increased (Fig. 5 bottom).

Figure 6

The typical pattern of the muscle layer proliferation and submucosa thickning. The thick dense-line, the thin dense-line, the thick dot-line and thin dot-line indicated the interface of two muscle layers, outer bordering of longitudinal muscle layer, the interface between muscle layer and submocosa layer, and the interface between submucosa layer and mucosa layer. The submucosa and muscle layers increased the thickness after the obstruction, the circumferential muscle layer increased much more than the longitudinal muscle layer.

Figure 7

The opening angles and residual strains of the intestinal segments are shown. All parameters were smaller after the obstruction when compared to those in the sham operation and normal groups.

Figure 8

Top panel: The circumferential stress-strain curves at longitudinal stretch ratio 1.1 in the groups. The stress-strain curves were shifted to the left after 7 days obstruction compared those with normal and sham control groups, indicating the intestinal wall became stiffer due to the obstruction. Bottom panel: The linear association between the constant a and the thickness of different layers. The strongest correlation was found between the constant a and the thickness of submucosa layer.