Mast cell degranulation during abdominal surgery initiates postoperative ileus in mice

Background & Aims: Inflammation of the intestinal muscularis following manipulation during surgery plays a crucial role in the pathogenesis of postoperative ileus. Here, we evaluate the role of mast cell activation in the recruitment of infiltrates in a murine model. Methods: Twenty-four hours after control laparotomy or intestinal manipulation, gastric emptying was determined. Mast cell degranulation was determined by measurement of mast cell protease-I in peritoneal fluid. Intestinal inflammation was assessed by determination of tissue myeloperoxidase activity and histochemical staining. Results : Intestinal manipulation elicited a significant increase in mast cell protease-I levels in peritoneal fluid and resulted in recruitment of inflammatory infiltrates to the intestinal muscularis. This infiltrate was associated with a delay in gastric emptying 24 hours after surgery. Pretreatment with mast cell stabilizers ketotifen (1 mg/kg, PO) or doxantrazole (5 mg/kg, IP) prevented both manipulation-induced inflammation and gastroparesis. Reciprocally, in vivo exposure of an ileal loop to the mast cell secretagogue compound 48/80 (0.2 mg/mL for 1 minute) induced muscular inflammation and delayed gastric emptying. The manipulation-induced inflammation was dependent on the presence of mast cells because intestinal manipulation in mast cell-deficient Kit Kit(v) mice did not elicit significant leukocyte recruitment. Reconstitution of Kit/Kit(v) mice with cultured bone marrow-derived mast cells from congenic wild types restored the manipulation-induced inflammation. Conclusions: Our results show that degranulation of connective tissue mast cells is a key event for the establishment of the intestinal infiltrate that mediates postoperative ileus following abdominal surgery.