Endotoxin In Rats Research Articles

TUMOR NECROSIS FACTOR ALPHA IS INVOLVED IN THE INDUCTION OF PLASMINOGEN ACTIVATOR INHIBITOR-1 BY ENDOTOXIN

Treatment with endotoxin leads to a rise in plasminogen activator inhibitor-1 (PAI-1) both in vivo and in vitro. Although a recent study insists that inhibition of tumor necrosis factor alpha (TNFα) does not reduce the induction of PAI-1 by endotoxin in rats, we imagine that TNFα is involved in the induction of PAI-1 by endotoxin, because endotoxin treatment induces TNFα and administration of TNFα induces PAI-1 both in vitro and in vivo. In order to confirm this hypothesis, we have measured plasma PAI activity and PAI-1 mRNA in liver after endotoxin treatment with or without pretreatment by polyclonal rabbit antiserum against murine TNFα. Chronically cannulated Sprague-Dawley rats received intravenous injection of endotoxin (10 μg/kg) 10 min after administration of anti-TNFα antibody (Antibody Group) or same volume of control rabbit serum (Control Group). PAI activity was measured by Coatest PAI®, ans PAI-1 mRNA was measured semi-quantitatively by high-performance liquid chromatography after reverse transcription and polymerase chain reaction. Increases in PAI activity 4 h after endotoxin treatment were significantly smaller in the Antibody Group than in the Control Group, while increases in PAI-1 mRNA were significantly smaller at 2 h in the Antibody Group. These results suggest that TNFα is responsible, at least in part, for the induction of PAI-1 by endotoxin in vivo. © 1997 Elsevier Science Ltd

Central involvement of kinin B1 and B2 receptors in the febrile response induced by endotoxin in rats.

1. The effect of central injection of selective kinin B1 and B2 receptor antagonists on the febrile response induced by endotoxin (E. coli lipopolysaccharide, LPS) in rats was investigated. 2. Intracerebroventricular (i.c.v.) injection of a selective B2 receptor antagonist (Hoe-140, 8 nmol) reduced the early (0-2 h), but increased the late phase (4-6 h) of the febrile response induced by intravenous (i.v.) injection of LPS (0.5 microgram kg-1). 3. Co-administration of Hoe-140 (8 nmol, i.c.v.) with LPS (0.5 microgram kg-1, i.v.), followed 2.5 h later by the i.c.v. injection of a selective B1 receptor antagonist [des-Arg9-Leu8]-bradykinin (BK, 8 nmol), significantly reduced the febrile response induced by LPS throughout the whole experimental period. 4. Intravenous injection of Hoe-140 (1 mg kg-1) significantly reduced the febrile response induced by LPS (0.5 microgram kg-1, i.p.). 5. Pretreatment (24 h) with LPS (0.5 microgram kg-1, i.v.) reduced the febrile response induced by BK or [Tyr8]-BK (both, 5 nmol, i.c.v.), but markedly increased the febrile response induced by [des-Arg9]-BK (5 nmol, i.c.v.). The response induced by [des-Arg9]-BK in LPS-pretreated rats was significantly inhibited by co-injection of [des-Arg9-Leu8]-BK (15 nmol, i.c.v.). 6. The results suggest that kinins are involved in the induction of LPS-induced fever and that central B2 and B1 receptors are activated during the initial and late phase of this response, respectively. The results also suggest that downregulation and/or desensitization of B2 receptors and induction and/or upregulation of B1 receptors in LPS-pretreated animals may have a significant pathophysiological role in the induction and maintenance of fever. These observations may be specifically important in the case of chronic inflammatory conditions, because the BK metabolite [des-Arg9]-BK, so far considered an inactive metabolite, acquires an active and relevant role with the progressive expression of B1 receptors that occurs in such states.

Pulmonary Lipocytes in the Production of Interstitial Fibrosis. † 1598

Pulmonary interstitial fibrosis is an important component of the pathology of bronchopulmonary dysplasia (BPD). There is increasing evidence to support the role of infection, especially sepsis, in the pathogenesis of BPD. We have investigated the effects of combining chronic oxygen toxicity and lipopolysaccharide endotoxin in rats. Our hypothesis is that endotoxin activates pulmonary macrophages in an O2 damaged lung, which in turn activates pulmonary lipocytes to release stored retinoids and, with chronicity, initiates production of TGF-b by these cells. In the liver paradigm of fibrosis, this is followed by development of receptors for PDGF on lipocytes leading to autocrine proliferation, transformation into myofibroblasts and the production of cross-linked collagens. Rats treated with 100% O2 for 36 hours, 90% O2 for 36 hours, 80% O2 for 6 weeks and IP endotoxin for 3 days beginning at 72 hours, showed early immunostaining of lung epithelium, lung lipocytes and of liver lipocytes with TGF-β3, which disappeared with chronicity by 36 days. PDGF immunostaining also appeared early in lung and liver lipocytes and persisted for 36 days. Alpha smooth muscle actin, which appears with lipocyte transformation to myofibroblasts,showed immunoreactivity in cells around respiratory bronchioles and at septal tips, increasing greatly with chronicity. The presence of collagen in alveolar walls and septal tips also increased with time as shown by van Gieson staining and by electron microscopy. We suggest that activation of pulmonary lipocytes is an important component of the production of cross-linked collagen and its deposition in pulmonary interstitial fibrosis.

Endotoxin-induced desensitization of THP-1 cells is not associated with altered G protein binding or content

In rats endotoxin tolerance is characterized by decreased endotoxin-stimulated peritoneal macrophage arachidonic acid metabolism and decreased GTP binding protein function. The hypothesis that THP-1 cells can be altered in a similar manner by pretreatment with endotoxin was tested. These studies examined endotoxin's ability to stimulate eicosanoid and tumor necrosis factor α (TNFα) in control and desensitized THP 1 cells. Additionally, membrane GTPγ 35S binding and Western blot analyses with specific antisera to G i1,2α, Gi3a, Gαcommon, and the β subunit of G in control and endotoxin-desensitized THP-1 cells were assessed. Endotoxin (10 μg/ml) stimulated thromboxane (Tx) B2 production in THP-1 cells. Pretreatment with pertussis toxin (PT), resulted in significant inhibition of TxB2 production at concentrations not inhibited by equimolar concentrations of PT-B protomer. The latter observations suggest a role of PT-sensitive G protein in endotoxin activation of THP-1 cells. Pre-exposure to endotoxin (1 μg/ml) for 18 h desensitized THP-1 cells to endotoxin-stimulated TxB2 production and endotoxin-stimulated TNFα. To determine if endotoxin pretreatment affects G protein function, THP-1 cell membranes were isolated from endotoxin pretreated and control cells for equilibrium binding with GTPγ35S, a nonhydrolyzable analog of GTP. Neither the total number of binding sites (Bmax) nor the dissociation constant (Kd) for GTPγ35S in desensitized THP-1 cells were significantly different from those of control cells. PT-catalyzed ADP-ribosylation of G proteins in control and LPS-desensitized THP-1 cells demonstrated no difference in the quantity of G protein labelled versus desensitized cells. Immunoblots also showed no difference between control and desensitized cells in the membrane content of specific heterotrimeric G proteins. The data demonstrate that pre-exposure to endotoxin desensitizes the cells subsequent endotoxin stimulation of mediator production. However, unlike the in vivo rat model, this is not associated with a decrease in G protein binding or content.

Role of bacterial adherence and the mucus barrier on bacterial translocation: effects of protein malnutrition and endotoxin in rats.

The purpose of the study was to investigate the potential relations between mucosal bacterial adherence, intestinal mucus and mucin content, and bacterial translocation. The attachment of bacteria to mucosal surfaces is the initial event in the pathogenesis of most bacterial infections that originate at mucosal surfaces, such as the gut. The intestinal mucus layer appears to function as a defensive barrier limiting micro-organisms present in the intestinal lumen from colonizing enterocytes. Consequently, studies focusing on the biology of bacterial adherence to the intestinal mucosa likely are to be important in clarifying the pathogenesis of gut origin sepsis. To explore the relations between intestinal bacterial adherence, mucus bacterial binding, and bacterial translocation, two models were used. One (protein malnutrition) in which profound alterations in intestinal morphology occurs in the absence of significant translocation and one (endotoxin challenge) in which bacterial translocation occurs and intestinal morphology is relatively normal. Protein malnutrition was not associated with bacterial translocation and measurement of enteroadherent, mucosally associated bacterial population levels documented that the total number of gram-negative enteric bacilli adherent to the ileum and cecum was less in the protein-malnourished rats than in the normally nourished animals (p < 0.01). Furthermore, there was an inverse relation between the duration of protein malnutrition and bacterial adherence to the intestinal mucosa (r = 0.62, p < 0.002). In contrast, after endotoxin challenge, the level of enteroadherent bacteria was increased and bacterial translocation was observed. The binding of Escherichia coli to immobilized ileal mucus in vitro was decreased significantly in protein-malnourished rats, whereas E. coli binding to insoluble ileal mucus was increased in the rats receiving endotoxin. This study indicates that the adherence of bacteria to the intestinal mucosal surface is an important factor in bacterial translocation, that intestinal mucus modulates bacterial adherence, and that increased levels of mucosally associated bacteria are associated with a loss intestinal barrier function to bacteria.

Effects of Plasma Kallikrein Specific Inhibitor and Active-site Blocked Factor VIIa on the Pulmonary Vascular Injury Induced by Endotoxin in Rats

The acute respiratory distress syndrome (ARDS) is a serious complication of sepsis. To evaluate the role of the coagulation system in the pathogenesis of ARDS in sepsis, we examined the effects of the administration of a synthetic plasma kallikrein specific inhibitor (PKSI) and of active-site blocked factor VIIa (DEGR-VIIa) on the pulmonary vascular injury induced by E. coli endotoxin (ET) in rats. Administration of PKSI prevented the pulmonary vascular injury induced by ET as well as pulmonary histological changes in animals administered ET, but it did not affect the intravascular coagulation. The opposite effect was seen with DEGR-VIIa, which prevented the intravascular coagulation but not the pulmonary vascular injury. PKSI did not inhibit the activation of the complement system induced by ET leading to the activation of neutrophils. Findings suggest that PKSI may prevent the pulmonary vascular injury induced by ET by inhibiting kallikrein, which activates the neutrophils. The intrinsic pathway of coagulation may be more important than the extrinsic pathway in the pulmonary vascular injury produced by ET.

Insoluble glycogen, a metabolizable internal adsorbent, decreases the lethality of endotoxin shock in rats

Insoluble glycogen is an enzymatically modified form of naturally occurring soluble glycogen with a great adsorbing capacity. It can be metabolized by phagocytes to glucose. In this study we used insoluble glycogen intravenously in the experimental endotoxin shock of rats. Wistar male rats were sensitized to endotoxin by Pb acetate. The survival of rats were compared in groups of animals endotoxin shock treated and non-treated with insoluble glycogen. Furthermore, we have determined in vitro the binding capacity of insoluble glycogen for endotoxin, tumour necrosis factor alpha, interleukin-1 and secretable phospholipase A2. Use of 10 mg/kg dose of insoluble glycogen could completely prevent the lethality of shock induced by LD50 quantity of endotoxin in rats. All animals treated survived. Insoluble glycogen is a form of ‘metabolizable internal adsorbents’. It can potentially be used for treatment of septic shock.

Targeting Naproxen to Non-Parenchymal Liver Cells Protects Against Endotoxin Induced Liver Damage

Non-steroidal anti-inflammatory drugs (NSAID's) could be of value in the treatment of liver disease; however, their use in this situation is limited by renal side effects. Therefore, we explored whether naproxen covalently bound to human serum albumin (NAP-HSA) was able to reduce toxicity in an acute model of liver disease induced by endotoxin in rats pretreated with Corynebacterium parvum. In the isolated perfused liver of such animals endotoxin induced cholestasis (0.62 ± 0.05 vs. 0.24 ± 0.09 μl.min-1.g liver-1; p < 0.05), increased vascular resistance (11300 ± 400 vs. 311000 ± 2000 dyn.s.cm-5; p < 0.05) and alanine aminotransferase release (22 ± 9 vs. 149 ± 40 IU/l; p < 0.05). At the highest dose tested (22 mg/kg, corresponding to 6.0 μmoles naproxen), NAP-HSA normalized ALT release (21 ± 10 IU/l; p < 0.05) while an equimolar amount of non-targeted naproxen was only partially effective (56 ± 19 IU/l). A conventional dose of naproxen similarly prevented transaminase release. Cholestasis and increased vascular resistance were also prevented by NAP-HSA. Drug targeting by linking drugs to proteins is a potentially useful approach to maximizing drug effect while minimizing adverse events; this could be particularly useful for compounds with potentially serious adverse effects in patients with chronic liver disease such as the nonsteroidal anti-inflammatory agents used in the present study.

Induction mechanism of small intestinal lesions caused by intravenous injection of endotoxin in rats.

The pathogenesis of intestinal damage caused by bolus intravenous injection of endotoxin (ETX; 3 mg/kg) was investigated. Administration of ETX to rats induced reddish discoloration suggestive of bleeding, increased hemoglobin amounts, and leakage of plasma protein in the intestine. However, light microscopic examination of the intestine demonstrated blood congestion of the microvessels. Plasma accumulation was partially inhibited by combined pretreatment with a histamine H1 antagonist and a serotonin (5-HT) antagonist. Neither a 5-lipoxygenase inhibitor, a soybean trypsin inhibitor, nor atropine was observed to inhibit plasma accumulation. Both the intestinal leakage of plasma and the accumulation of hemoglobin were completely inhibited by indomethacin, a selective thromboxane A synthetase inhibitor (OKY 1581), and a stable PGI2 analogue (beraprost). Intravital microscopic observation of the microvessels of the small intestinal villi demonstrated microthrombus formation within several minutes after the injection of ETX, and pretreatment with OKY 1581 attenuated the formation of microthrombus. Platelet counts decreased significantly 10 min after ETX administration, and the decrease was not inhibited by pretreatment with either OKY 1581 or beraprost. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were not prolonged. These observations thus suggest that microcirculatory disturbances by platelet thrombus, which are mediated by thromboxane A2 at least in part, play an important role in ETX-induced intestinal damage.

Endotoxin stimulates the expression of group II PLA2 in rat lung in vivo and in isolated perfused lungs.

Injection of endotoxin in vivo leads to increased phospholipase A2 (PLA2) activity in the lung, but neither the type(s) of PLA2 involved nor the importance of blood components and/or different inflammatory cytokines has been clarified. In the present study, injection of endotoxin in rats caused increased lung levels of group II PLA2, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-1 beta mRNA, while group I PLA2 mRNA levels were unaffected. The augmented group II PLA2 mRNA levels corresponded to a rise in membrane-associated PLA2 enzymatic activity that was inhibited by rutin, an inhibitor of group II PLA2. In blood-free, salt-perfused lungs, addition of endotoxin to the perfusate caused elevated group II PLA2, TNF-alpha, and IL-1 beta mRNA levels and release of PLA2 and TNF-alpha activity into the perfusate, and when instilled intratracheally, endotoxin caused increased PLA2 activity in the lung tissue. It is concluded that 1) endotoxin stimulates group II PLA2, but not group I PLA2, in rat lung cells, 2) this stimulation is accompanied by increased expression of TNF-alpha and IL-1 beta, and 3) endotoxin-induced PLA2 activation and cytokine production in the lung are not dependent on circulating blood components.

Growth hormone potentiates the in vivo biological activities of endotoxin in the rat.

To investigate if growth hormone (GH) alters the effects of endotoxin in rats, endotoxin (5 mg kg-1 body weight) was injected into normal rats and into rats primed with GH for 3 days. Endotoxin had injurious effects on renal and liver function and induced hypoglycaemia and hyperlipidaemia as expected. GH-primed rats became extremely sick after endotoxin challenge and had more marked abnormalities of renal and liver function and much more pronounced hypoglycaemia and hyperlipidaemia than non-primed rats. It is concluded that growth hormone potentiates the in vivo biological activities of endotoxin in the rat. The results may also suggest that caution should be exerted when considering GH treatment in catabolic situations with endotoxaemia and that special attention should be paid to the prevention of infection during GH therapy in such situations.

Aerosolized and instilled surfactant therapies for acute lung injury caused by intratracheal endotoxin in rats

To compare the effects of surfactant replacement by aerosol inhalation and bolus instillation on acute lung injury caused by the intratracheal injection of endotoxin in rats. Prospective, randomized study. University Laboratory. Male Wistar rats weighing 368 +/- 31 (SD) g. Escherichia coli endotoxin (57 +/- 20 mg/kg) was injected into the tracheas of 36 anesthetized and mechanically ventilated rats (FIO of 1.0). When the PaO2 had decreased to <200 torr (<26.7 kPa), the rats were randomly assigned to one of three groups: a control group (n=12)given no material; a bolus group (n=12) given a modified natural surfactant suspension (100 mg/kg in 2.0 mL/kg saline) by bolus instillation into the trachea; and an aerosol group (n=12) given surfactant aerosolized with an ultra-sonic nebulizer for 60 mins. Bolus instillation transiently decreased the mean blood pressure by approximately 30%. However, aerosol inhalation did not. The PaO2 values of the control group remained <90 torr (<12.0 kPa) until the end of the experiment (180 mins). In contrast, the PaO2 of the bolus group increased to 387 +/- 134 torr (51.6 +/- 17.9 kPa; p<.05 vs. other groups) 15 mins after surfactant replacement, and remained at approximately 400 torr (approximately 53.3 kPa) throughout the experiment. The PaO2 values of the aerosol group increased slowly, peaked at 240 +/- 109 torr (32.0 +/- 14.5 kPa; p<.05 vs. the control group) 60 mins after the start of surfactant replacement, and remained at approximately 200 torr (approximately 26.7 kPa). Bolus instillation was superior to aerosol inhalation concerning maximum efficacy, the rapid onset of therapeutic effects, and the necessary dose of surfactant. However, aerosol that does not cause hypotension may be of use in the treatment of adult respiratory distress syndrome in patients with circulatory instability.

Involvement of central histamine in the early phase of ACTH and corticosterone responses to endotoxin in rats.

The involvement of histaminergic transmission in the rapid and sustained plasma ACTH and corticosterone (CORT) responses induced in conscious rats by intra-arterial infusions of 25 micrograms.kg-1 Escherichia coli lipopolysaccharide (LPS) was investigated. LPS challenge produced a rapid and transient increase (+ 62%) in the amount of histamine (HA) in the median eminence 15 min after LPS administration, which contrasted with constant concentrations of plasma HA throughout the entire study (up to 480 min). Blockade of histaminergic receptors by intra-arterial pretreatment with H1 or H2 antagonists (mepyramine, 1 mg/rat, and cimetidine, 2 mg/rat), administered separately, did not affect either ACTH or CORT responses to LPS. Pretreatment with the same doses of the two antagonists in combination very significantly but transiently impaired the earliest phase (30 min) of the ACTH and CORT responses, without any apparent effect on the late phase of these responses. Pretreatment of the animals with an H3-receptor agonist (R alpha-methylhistamine dihydrochloride, 1 mg/rat) similarly blunted the early corticotropic responses to LPS, and also slightly depressed the long-lasting CORT response. These findings support the view that activated central HA transmission may be a key intermediate mechanism triggering the CRH41-ACTH-CORT responses to LPS, in addition to the previously demonstrated activating role of catecholaminergic afferences to the CRH41 neurons during this early complex phase of corticotropic response to LPS.

Synthetic Protease Inhibitor Prevents Impaired Hepatic Secretion of Lysosomal Enzymes into Bile and Hepatic Lysosomal Fragility Induced by Endotoxin in Rats

This study was designed to examine the effect of sepsis on the hepatic functions, particularly from the view point of hepatic lysosomal functions. Endotoxemia was produced in rats by intravenous injection of endotoxin (1 mg/kg), and at 6 h after the injection of endotoxin, we studied (1) the hepatic secretion of lysosomal enzymes (β-glucuronidase, β-galactosidase and N-acetyl-β-glucosaminidase) into bile in the isolated perfused rat liver model; (2) the aspartate aminotransferase (ASAT), alanine aminotransferase (ALAT) and lysosomal enzyme levels in the effluent in the isolated liver model; (3) hepatic lysosomal fragility in an in vitro incubation study; (4) protective effect of a new synthetic protease inhibitor, sepinostat mesilate (FUT-187) against hepatic injuries induced by endotoxin. Decreased hepatic secretion of lysosomal enzymes into bile and accelerated hepatic lysosomal fragility were observed in endotoxemia. FUT-187 showed significant protective effects against these hepatic injuries induced by endotoxin. These results indicate that impaired hepatic functions, depressed hepatic secretion of lysosomal enzymes into bile, and increased hepatic lysosomal fragility, seem to be closely related to the hepatic injuries induced by endotoxin. These results also indicate that some unknown protease activities, which are susceptible to inhibition by FUT-187, seem to play an important role in the development of hepatic injuries induced by endotoxin.

Changes of neurotensin and endotoxin in rats with intestinal ischemia

Changes of neurotensin and endotoxin in rats with intestinal ischemia

Temporal relationships between levels of circulating NO derivatives, vascular NO production and hyporeactivity to noradrenaline induced by endotoxin in rats

Temporal relationships between levels of circulating NO derivatives, vascular NO production and hyporeactivity to noradrenaline induced by endotoxin in rats

Temporal relationships between levels of circulating NO derivatives, vascular NO production and hyporeactivity to noradrenaline induced by endotoxin in rats

Lipopolysaccharide (LPS) induces early (within 1 h) and delayed (after several hours) impairment of vascular reactivity to catecholamines whose mechanisms are different, although they probably both involve nitric oxide (NO). Temporal and quantitative relationships between hyporeactivity to noradrenaline and NO production were investigated in a rat model of endotoxaemia allowing to clearly distinguish the two phases of hyporeactivity. Anaesthetised rats were infused with LPS (14 mg kg-1 h-1) for 1 h. Pressure responses to noradrenaline (NA) and circulating NO derivatives (nitrosyl haemoglobin, NO2-, NO3-) were monitored for 5 h after the onset of infusion. Reactivity to NA and tissue cyclic GMP level were also assessed ex vivo, in aortic rings taken at different experimental times. LPS-induced early hyporeactivity to NA was associated with a moderate but significant increase in plasma NO3- level, without any significant change in concentration of the other circulating NO derivatives. Neither reactivity ex vivo nor cyclic GMP content were modified in aortae taken after 1 h of LPS infusion. By contrast, delayed hyporeactivity (5 h after the onset of LPS infusion) was associated with a large increase in all circulating NO derivatives (up to 2.5 fold), enhanced aortic cyclic GMP level and aortic hyporeactivity ex vivo. Pre-treatment of rats with NG-nitro-L-arginine methyl ester (1 mg kg-1 i.v.) entirely prevented early hyporeactivity and rise in NO3- concentration. In addition it attenuated in comparable proportion both delayed hyporeactivity to NA in vivo and circulating levels of NO derivatives. The results confirm the involvement of NO in the two phases of hyporeactivity to NA induced by LPS. They strongly support the view that a circulating factor is involved in triggering endothelial NO release during the early phase, whereas the delayed phase is associated with a high production of NO in vascular smooth muscle resulting from the induction of NO synthase.

Hirulog effect in rat endotoxin shock

Hirulog TM is a thrombin catalytic site inhibitor which exhibits specificity for the anionic binding exosite of alpha thrombin. Here, we have evaluated the effect of Hirulog TM (1, 5 and 10 mg/kg, 30 min pretreatment) in a rat model of endotoxemia. Intravenous injection of lipopolysaccharide from E. coli (25 mg/kg; serotype 0127:B8) caused decreases in blood pressure which were significantly reduced (about 60%) in animals pretreated with Hirulog TM. Rat survival to endotoxin was significantly increased in Hirulog TM pretreated group (5 and 10 mg/kg) up to 24 hours. Hirulog TMat the dose of 10 mg/kg inhibited both endotoxin-induced leukopenia at 30 and 60 minute points and thrombocytopenia at 30 minute point but not at 90 and 120 minute points. Fibrinogen levels were significantly reduced after 2 hours following endotoxin administration. Pretreatment with Hirulog TM (5–10 mg/kg i.v.) 30 min prior to administration of endotoxin prevented changes in fibrinogen plasma levels. These results demonstrate that Hirulog TM-induced inhibition of thrombin is effective in reducing toxic and lethal effects of endotoxin.

P.90 Effects of different chemically defined structuredlipids on bacterial sequestration and liver morphology in an endotoxin rat model

P.90 Effects of different chemically defined structuredlipids on bacterial sequestration and liver morphology in an endotoxin rat model

Protective effect of DS-4574, a peptidoleukotriene receptor antagonist, against endotoxin-induced intestinal injury in rats

We evaluated the protective effect of DS-4574 (6-(2-cyclohexylethyl)-[1,3,4]thiadiazolo[3,2- a]-1,2,3-triazolo[4,5- d]pyrimidin-9(3 H)-one), a peptidoleukotriene receptor antagonist, against intestinal mucosal injury evoked by endotoxin in rats by exploring changes in hematocrit and plasma leakage along with morphological features. Treatment with Escherichia coli endotoxin (5 mg/kg i.v.) alone elicited hemoconcentration, vasocongestion and a marked mucosal necrosis. DS-4574 (10–50 mg/kg) effectively prevented these changes on either oral or intraduodenal administration. These results demonstrate that peptidoleukotrienes may be key mediators in the intestinal injury induced by endotoxin in rats.