Experimental study of the effect of nitric oxide inhibition on mesenteric blood flow and interleukin-10 levels with a lipopolysaccharide challenge.

The septic shock-induced decrease in mesenteric blood flow and release of proinflammatory cytokines are among the major pathophysiologic changes presumed to lead to multiple organ dysfunction syndrome (MODS). Increased nitric oxide (NO) levels are associated with both decreased mesenteric blood flow and positive modulation of proinflammatory cytokine release. In this study we aimed to determine the effect of the timing of the inhibition of nitric oxide synthase (NOS) on mesenteric blood flow and serum interleukin-10 (IL-10) concentrations during endotoxin shock. A nonspecific NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME), a specific NOS inhibitor aminoguanidine (AG), or placebo were injected 20 minutes before or 20 minutes after a lipopolysaccharide (LPS) or placebo challenge to Swiss-albino mice, as pretreatment or posttreatment, respectively. At 120 minutes after LPS or placebo injection the mesenteric blood flow was measured, and blood samples from the heart were obtained for IL-10 levels in both groups. Pretreatment and posttreatment with both NOS inhibitors prevented the LPS-induced decrease in mesenteric blood flow. Pretreatment was more effective for this purpose. Pretreatment accentuated the LPS-induced increase in serum IL-10 concentrations, whereas posttreatment had no significant effect. We conclude that the timing of NOS inhibition is important for attenuating some deleterious effects of endotoxin.

Aminoguanidine attenuates endotoxin-induced mesenteric vascular hyporeactivity.

BACKGROUND: The aim of this study was to investigate the effects of inducible nitric oxide synthase inhibition by aminoguanidine on endotoxin-induced reduction in mesenteric blood flow. METHODS: Twenty Sprague-Dawley rats (180-230 g) allocated into four groups were administered either Escherichia coli endotoxin 1 mg/kg intraperitoneally or its solvent saline and were pretreated with either aminoguanidine (15 mg/kg intraperitoneally 20 min before and 2 h after endotoxin injection) or saline. Some 4 h after endotoxin injection, animals were anaesthetized, arterial blood pressure and mesenteric blood flow were measured and the resistance in the mesenteric vascular beds was then calculated. The effect of phenylephrine (1-30 microg/kg intravenously) on these parameters was also investigated. RESULTS: Endotoxin did not significantly modify the mean arterial blood pressure but decreased mesenteric blood flow by increasing the vascular resistance (mean(s.e.m.) 7.8(1.0) versus 13.7(1.2) mmHg per min per ml for control versus endotoxin groups; n = 5, P = 0.0099). Aminoguanidine alone had no effect on either the mean arterial blood pressure or mesenteric blood flow, but it completely blocked the effects of endotoxin. On the other hand, endotoxin significantly attenuated the responsiveness to phenylephrine which was restored by aminoguanidine. CONCLUSION: The present results indicate that endotoxin decreases the mesenteric vascular blood flow by increasing vascular resistance and decreases responsiveness to phenylephrine. The effects of endotoxin were inhibited by aminoguanidine. The mesenteric vasoconstriction in response to endotoxin might not be explained by the overproduction of nitric oxide; other actions of aminoguanidine may explain its inhibitory effect. Presented in part to the 10th Annual Meeting of the Surgical Infection Society - Europe, Istanbul, Turkey, May 1997

Evidence that aminoguanidine inhibits endotoxin-induced bacterial translocation.

BACKGROUND: The role of inducible nitric oxide synthase (iNOS) in endotoxin-induced bacterial translocation was investigated by using its specific blocker aminoguanidine in 46 albino mice (25-35 g) allocated into four groups. METHODS: The first group received intraperitoneal saline (control; 0.9 per cent w v(-1) sodium chloride 1 ml kg(-1); n=6), the second group intraperitoneal endotoxin (Escherichia coli lipopolysaccharide 055:B5 20 mg kg(-1); n=19), the third group intraperitoneal aminoguanidine (20 mg kg(-1), 20 min before and 12 h after saline; n=6) and the fourth group both endotoxin and aminoguanidine intraperitoneally (n=15). Some 24 h later, the animals were anaesthetized with ether and blood samples were collected by cardiac puncture together with mesenteric lymph node (MLN), spleen and liver specimens under aseptic conditions. Specimens were then cultured to determine the presence of colony-forming units as an index of bacterial translocation. RESULTS: No bacterial growth was detected in samples from the first and third groups. Colony-forming bacteria were found in ten of 14 MLN samples, eight of 14 spleens, four of 14 livers and three of 14 peripheral blood samples in the second group, with E. coli being the predominant pathogen. In contrast, in the fourth group, colony-forming bacteria were found in only three of 14 MLN samples (P=0.02 versus the second group), three of 14 spleens and one of 14 liver specimens. None of the values in the fourth group was significantly different from those in the saline control group. CONCLUSION: The inhibition of iNOS during endotoxaemia by its specific blocker aminoguanidine attenuates the incidence of bacterial translocation in mice. These results may be exploited clinically for the prophylaxis and treatment of septic states.

Factors that may increase morbidity in a model of intra-abdominal contamination caused by gallstones lost in the peritoneal cavity.

OBJECTIVE: To assess the effect of intraperitoneal gallstones with and without Escherichia coli and sterile bile on the incidence of intraperitoneal complications in mice. DESIGN: Prospective randomised study. SETTING: Teaching hospital, Turkey. MATERIAL: 180 Swiss albino mice in five groups, n = 20 in the control group, and n = 40 in each of the experimental groups. INTERVENTIONS: Group A laparotomy alone (controls); group B, laparotomy amd intraperitoneal instillation of E. coli 4 x 10(6) 0.1 ml; group C, laparotomy and insertion of sterilised gallstones; group D, laparotomy, insertion of gallstones and instillation of E. coli 4 x 10(6) 0.1 ml; and group E, laparotomy, insertion of gallstones, and instillation of E. coli 4 x 10(6) 0.1 ml and sterile bile 0.1 ml. A quarter of each group was killed after 1, 2, 4, and 8 weeks. MAIN OUTCOME MEASURES: Intra-peritoneal abscesses, adhesions, perforations, fistula, or obstruction. RESULTS: No mice died. Adhesions were found in 3(15%), 7(18%), 30(75%), 25(63%), and 24(60%) in the five groups, respectively. No mice in groups A, B, or C developed an abscess, but 8 did in each of groups D and E (20%). One mouse in group D developed obstruction. Logistic regression showed that abscess formation was significantly increased by the addition of gallstones and E. coli to the peritoneal cavity (p < 0.001) but the addition of bile had no effect. Gallstones increased the rate of adhesions more than nine fold (p < 0.001) but E. coli with or without bile had no effect (p = 0.75). CONCLUSIONS: Free gallstones within the peritoneal cavity with or without E. coli or sterile bile, or both, increased the rate of formation of both abscesses and adhesions in mice. These results suggest that efforts should be made retrieve gallstones that are dropped into the peritoneal cavity during laparoscopic cholecystectomy, particularly in patients with acute cholecystitis.