Surgically induced leukocytic infiltrates within the rat intestinal muscularis mediate postoperative ileus

Background and Aims: Postoperative ileus is a poorly understood and common problem. We previously demonstrated an association between a suppression in jejunal circular muscle activity and a massive extravasation of leukocytes into the muscularis after surgical manipulation of the small bowel. This study was pursued to establish a direct causal link between these events. Methods: Reverse-transcription polymerase chain reaction and immunohistochemistry were used to detect and localize expression of adhesion molecules: P-selectin, intercellular adhesion molecule 1 (ICAM-1), and lymphocyte function-associated antigen 1 (LFA-1). Leukocyte infiltration and in vitro jejunal circular muscle function were quantified in controls and manipulated animals with and without antibody treatment (1A29, WT.1, and WT.3). Results: Surgical manipulation caused a significant up-regulation within the muscularis of ICAM-1 and P-selectin messenger RNA. ICAM-1 and P- selectin protein expression was increased within the muscularis microvasculature, and ICAM-1 and LFA-1 were expressed on infiltrating cells. Administration of adhesion molecule antibodies prevented the recruitment of monocytes and neutrophils into the muscularis and also averted jejunal circular muscle dysfunction. Conclusions: The data demonstrate that adhesion molecule antibodies prevent surgically induced suppression of intestinal muscle contractions and therefore suggests that late postoperative ileus is mediated through a leukocytic inflammatory response within the intestinal muscularis externa.