Roles of IL-1 and TNF in the decreased ileal muscle contractility induced by lipopolysaccharide.

Gastrointestinal stasis during sepsis may be associated with gastrointestinal smooth muscle dysfunction. Endotoxin [lipopolysaccharide (LPS)] impairs smooth muscle contraction, in part through inducible nitric oxide synthase (NOS II) and enhanced nitric oxide production. We studied the roles of tumor necrosis factor-alpha (TNF) and interleukin-1 (IL-1) in this process by using TNF binding protein (TNFbp) and IL-1 receptor antagonist (IL-1ra). Rats were treated with TNFbp and IL-1ra, or their vehicles, 1 h before receiving LPS or saline. At 5 h after LPS, contractility was measured in strips of ileal longitudinal smooth muscle, and NOS II activity was measured in full-thickness segments of ileum. LPS decreased maximum stress (mean +/- SE) from 508 +/- 55 (control) to 355 +/- 33 g/cm2 (P < 0.05). Pretreatment with TNFbp plus IL-1ra prevented the LPS-induced decrease. Separate studies of TNFbp alone or IL-1ra alone indicated that, at the doses and timing used, TNFbp was more effective. LPS also increased NOS II activity by >10-fold (P < 0.01) over control. This increase was prevented by TNFbp plus IL-1ra (P = not significant vs. control). We conclude that the LPS-induced increase in NOS II activity and the decrease in ileal muscle contractility are mediated by TNF and IL-1.

Decreased ileal muscle contractility and increased NOS II expression induced by lipopolysaccharide.

This study was designed to determine if an increase in nitric oxide synthase (NOS) activity induced by lipopolysaccharide (LPS) is associated with increases in NOS II protein and mRNA abundance and with altered ileal longitudinal muscle contractility. Strips of muscle taken from LPS-treated, but not control, animals exhibited reduced in vitro contractility when L-arginine was a component of the physiological salt solution. This reduction was reversed by N omega-nitro-L-arginine (L-NNA), a competitive inhibitor of NOS. Full-thickness segments of jejunum, ileum, and colon taken 5 h after LPS injection exhibited increased NOS activity, NOS II immunoreactivity, and NOS II mRNA abundance. Increased NOS II immunoreactivity and mRNA abundance also were detected in ileal muscle strips taken from LPS-treated animals. These data confirm the reported effects of LPS on intestinal NOS activity and indicate that it can be attributed, at least in part, to an increase in NOS II mRNA and protein abundance. Furthermore, the data suggest that an LPS-induced increase in NOS II may lead to a decrease in ileal muscle contractility.