Effects of endotoxin on regulation of intestinal smooth muscle nitric oxide synthase and intestinal transit

Background. The disrupted intestinal transit during endotoxemia may be medi ated by nitric oxide (NO). We hypothesized that the isoforms of nitric oxid e synthase (NOS) are up-regulated in intestinal smooth muscle during endoto xemia and that the scavenging of SO will normalize transit. Methods. Rats were given Escherichia coli lipopolysaccharide (LPS) 10 mg/kg intra intravenously and were killed 4 hours later. To determine the activi ty of NOS isoforms in the jejunum and ileum, the conversion of tritiated L- arginine to tritiated L-citrulline was measured. Western immunoblots were p erformed by incubating the extracted protein with specific polyclonal antib odies. To determine intestinal transit, rats were divided into 4 groups: 0. 9% sodium chloride 1 mL/h intravenously for 5 hours, LPS 10 mg/kg intraveno us bolus plus 1 mL/h 0.9% sodium chloride intravenously LPS plus oxyhemoglo bin 0.5 g/kg/h intravenously and oxyhemoglobin 0.5 g/kg/h intravenously. Results, LPS increased the constitutive and inducible NOS enzyme activities in the the jejunum and ileum. Western blots demonstrated that LPS up-regul ates both the NOS1 and NOS2 isoforms in jejunal and ileal smooth muscle. Ox yhemoglobin alone increased intestinal transit compared with controls, wher eas endotoxemia increased intestinal transit, which was ameliorated with in fusions of oxyhemoglobin. Conclusions. NO may Play a major role in mediating the rapid intestinal tra nsit induced by endotoxemia.