The effect of peroxynitrite on sphincter of Oddi motility

Effects of bioactive agents on biliary motor function

Our understanding of biliary motility under normal and pathophysiologic conditions is still incomplete, but there have been recent advances. Of particular interest are the mechanisms involved in gallbladder filling and emptying, with a focus on understanding the processes underlying impaired gallbladder emptying leading to gallbladder dyskinesia and the formation of gallstones or cholecystitis. The sphincter of Oddi (SO) is a complex neuromuscular structure. Recent studies have attempted to unravel the specific neural or hormonal mechanisms operating under normal physiologic conditions and those that may lead to SO dysfunction. Furthermore, new research fronts are emerging, including the role of leptin in obese patients with impaired biliary motility and the action of electroacupuncture for possible treatment of SO dysfunction. This review illustrates the broad front of current research regarding the effects of bioactive agents on biliary motility, including enteric hormones, nitric oxide, opioids, inflammatory mediators, leptin, protease inhibitors, neurotransmitters, and electroacupuncture.

Lipopolysaccharide temporarily impairs sphincter of Oddi motility

The aim of our study was to determine the effect of lipopolysaccharide (LPS) on sphincter of Oddi (SO) motility. Opossums received saline, Escherichia coli LPS (1.0 mg/kg), or E. coli LPS (1.0 mg/kg) and aminoguanidine (50 mg/kg), and the SO was removed 6-24 h later. At 12 h LPS decreased electrical field stimulation (EFS)-induced relaxation and increased baseline tone. These changes were reversed when the animals were pretreated with aminoguanidine. The dose-dependent decrease in EFS-induced relaxation by N(omega)-nitro-l-arginine was impaired after LPS, but not in animals that received LPS and aminoguanidine. The impaired EFS-induced relaxation after LPS was reversed when l-arginine was added to the tissue bath. Serum levels of NO(-)(2)/NO(-)(3) were increased with LPS as compared to saline or both LPS and aminoguanidine. Inducible nitric oxide synthase mRNA was readily seen in SO segments after LPS. LPS impairs EFS-induced relaxation and increases baseline tone of the SO. The effects of LPS on SO motility appear to be mediated by nitric oxide.

Different types of contractions in rat colon and their modulation by oxidative stress

The aim of this study was to investigate the modulation of in vitro rat colonic circular muscle contractions by dextran sodium sulfate (DSS)-induced inflammation and in spontaneous inflammation in HLA-B27 rats. We also examined the potential role of hydrogen peroxide (H(2)O(2)) in modulating excitation-contraction coupling. The muscle strips from the middle colon generated spontaneous phasic contractions and giant contractions (GCs), the proximal colon strips generated primarily phasic contractions, and the distal colon strips were mostly quiescent. The spontaneous phasic contractions and GCs were not affected by inflammation, but the response to ACh was suppressed in DSS-treated rats and in HLA-B27 rats. H(2)O(2) production was increased in the muscularis of the inflamed colon. Incubation of colonic muscle strips with H(2)O(2) suppressed the spontaneous phasic contractions and concentration and time dependently reduced the response to ACh; in the middle colon, it also increased the frequency of GCs. We conclude that H(2)O(2) mimics the suppression of the contractile response to ACh in inflammation. H(2)O(2) also selectively suppresses phasic contractions and increases the frequency of GCs, as found previously in inflamed dog and human colons.