Novel method for studying postoperative ileus in mice

Abstract

Introduction: Postoperative ileus (POI) is characterized by a transient inhibition of coordinated motility of the gastrointestinal (GI) tract after abdominal surgery and leads to increased morbidity and prolonged hospitalization. Currently, intestinal manipulation of the intestine is widely used as a preclinical model of POI. The technique used to manipulate the intestine is however highly variable and difficult to standardize, leading to large variations and inconsistent findings between different investigators. Therefore, we developed a device by which a fixed and adjustable pressure can be applied during intestinal manipulation.

Methods: The standardized pressure manipulation method was developed using the purpose-designed device. First, the effect of graded manipulation was examined on postoperative GI transit. Next, this new technique was compared to the conventional manipulation technique used in previous studies. GI transit was measured by evaluating the intestinal distribution of orally gavaged fluorescein isothiocyanate (FITC)-labeled dextran. Infiltration of myeloperoxidase positive cells and cytokine production (ELISA) in the muscularis externa of the intestine were assessed.

Results: Increasing pressures resulted in a graded reduction of intestinal transit and was associated with intestinal inflammation as demonstrated by influx of leukocytes and increased levels of IL-6, IL-1β and MCP-1 compared to control mice. With an applied pressure of 9 grams a similar delay in intestinal transit could be obtained with a smaller standard deviation, leading to a reduced intra-individual variation.

Conclusions: This method provides a reproducible model with small variation to study the pathophysiology of POI and to evaluate new anti-inflammatory strategies.

Keywords: Gastrointestinal motility and physiology; inflammation; intestinal transit; mice; postoperative ileus.

Figure 1

Different degrees of manipulation of the small intestine induced a dose-dependent delay in gastrointestinal (GI) transit. A: Twenty-four hours after intestinal manipulation (IM), GI transit was determined by the calculation of the Geometric Center (GC). The GC was significantly decreased after manipulation with a pressure of 5.5 and 9 grams. B & C: Twenty-four hours after IM, muscular inflammation was determined by counting the number of MPO positive cells in the muscularis of the small intestine (B) and colon (C). The number of MPO positive cells was significantly increased after manipulation, but no significant differences between the groups with different degrees of standardized pressure manipulation were found. Statistical analysis was done by one-way analysis of variance (ANOVA) followed by Dunnett’s Multiple Comparison Test; * P < 0.05 compared to laparotomy (L). Bars indicate mean ± SEM. Figure 1A & B: L: n = 4; L + externalization of small intestine and cecum (L+E): n = 5-6; IM: n = 5-8 mice per group. Figure 1C: L: n = 4; L+E: n = 5; IM: n = 2-4 mice per group. Panel D | Construction drawing of the device to apply standardized manipulation of the small intestine.

Figure 2

Different degrees of manipulation of the small intestine induced a pressure-dependent production of proinflammatory cytokines. A-C: Twenty-four hours after intestinal manipulation (IM), cytokine production in the muscle layer of the small intestine was determined by ELISA. IL-6 (Panel A), IL-1β (Panel B) and MCP-1 (Panel C) levels were significantly increased after manipulation with a pressure of 5.5 grams. Statistical analysis was done by one-way analysis of variance (ANOVA) followed by Dunnett’s Multiple Comparison Test; * P < 0.05 compared to laparotomy (L). Bars indicate mean ± SEM. L: n = 3, L + externalization of small intestine and cecum (L+E): n = 5, IM: n = 3-6 per group. Panel D | Both conventional intestinal manipulation (IM) and standardized pressure IM of the small intestine induced a delay in gastrointestinal (GI) transit. Twenty-four hours after IM, GI transit was determined by the calculation of the Geometric Center (GC). The GC was significantly decreased by both methods, but standardized pressure manipulation resulted in a smaller variation. Statistical analysis was done by one-way analysis of variance (ANOVA) followed by Dunnett’s Multiple Comparison Test; * P < 0.05 compared to laparotomy. Bars indicate mean ± SD. Laparotomy: n = 7; conventional IM: n = 14; standardized IM: n = 12.