Intra-Abdominal Activation of a Local Inflammatory Response Within the Human Muscularis Externa during Laparotomy

Objective: To investigate the initiation of a complex inflammatory response within the human intestinal muscularis intraoperatively so as to determine the clinical applicability of the inflammatory hypothesis of postoperative ileus. Summary Background Data: Mild intestinal manipulation in rodents initiates the activation of transcription factors, upregulates proinflammatory cytokines, and increases the release of kinetically active mediators (nitric oxide and prostaglandins), all of which results in the recruitment of leukocytes and a suppression in motility (i.e., postoperative ileus). Methods: Human small bowel specimens were harvested during abdominal procedures at various times after laparotomy. Histochemical and immunohistochemical techniques were applied to intestinal muscularis whole-mounts. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed for interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). Signal transducers and activators of transcription (STAT) protein phosphorylation was determined by electromobility shift assay. Organ bath experiments were performed on jejunal circular smooth muscle strips. GW274150C and DFU were used in vitro as iNOS and COX-2 inhibitors. Results: Normal human muscularis externa contained numerous macrophages that expressed increased lymphocyte function associated antigen-1 (LFA-1) immunoreactivity as a function of intraoperative time. RT-PCR demonstrated a time-dependent induction of IL-6, IL-1β, TNF-α iNOS, and COX-2 mRNAs within muscularis extracts after incision. Mediators were localized to macrophages with STAT protein activation in protein extracts demonstrating local IL-6 functional activity. DFU alone or in combination with GW274150C increased circular muscle contractility. Specimens harvested after reoperation developed leukocytic infiltrates and displayed diminished in vitro muscle contractility. Conclusions: These human data demonstrate that surgical trauma is followed by resident muscularis macrophage activation and the upregulation, release, and functional activity of proinflammatory cytokines and kinetically active mediators.