Induction of IL-6 within the rodent intestinal muscularis after intestinal surgical stress

Background. Postoperative ileus is a poorly understood surgical problem characterized by leukocyte extravasation into the intestinal muscularis and suppression in muscle function. The study objective was to delineate a mechanistic inflammatory cascade initiated by intestinal manipulation. Methods. ACI and Sprague-Dawley rats, and IL-6^+/+ and IL-6^-/- mice were subjected to intestinal manipulation. One group of rats received adhesion molecule-blocking antibodies (1A29 and WT.3) before intestinal manipulation. Interleukin-6 (IL-6) messenger RNA (mRNA) levels and electrophoretic mobility shift assay for signal transducers and activators of transcription (STAT) activation were measured in tissue extracts. IL-6 protein levels were assessed by immunohistochemistry and enzyme-linked immunosorbent assay. Results. IL-6 mRNA from muscularis extracts demonstrated a significant induction after intestinal manipulation. No IL-6 induction was observed in mucosal extracts. Adhesion molecule blockade resulted in a marked decrease of cellular infiltration but did not change IL-6 mRNA expression in muscularis extracts. Resident macrophages in the muscularis stained for IL-6 by immunohistochemistry after intestinal manipulation. The isolated manipulated muscularis demonstrated a significant increase in IL-6 release. Electrophoretic mobility shift assay of manipulated muscularis showed a marked increase in IL-6-dependent Stat3 activation. Conclusions. This study demonstrates that manipulation of the small bowel during an abdominal operation initiates downstream induction, translation, release, and functional activity of IL-6 within the muscularis.