The experiment evaluated the effects of intravenous administration of polymyxin B on experimental endotoxaemia in sheep. Twenty clinically healthy fat-tailed sheep were randomly divided into: a group treated with 6,000 U/kg of polymyxin B, a group at 12,000 U/kg, and positive and negative controls. Endotoxaemia was induced by intravenous administration of lipopolysaccharide (LPS) from E. coli serotype O55:B5 at 0.5 μg/kg. polymyxin was infused intravenously along with 2.5 L of isotonic intravenous fluids at 20 mL/kg/h. The positive control group received LPS and 2.5 L of isotonic fluids, the negatives receiving just 2.5 L of isotonic fluids. Clinical signs were evaluated before and at 1.5, 3, 4.5, 6, 24, and 48 h after LPS administration. Blood was also sampled at the denoted hours and serum haptoglobin, tumour necrosis factor-α (TNF-α), and plasma lactate concentrations were assayed. The serum concentration of TNF-α in the positive control group increased significantly up to 48 h after LPS administration. The concentration of TNF-α was significantly different from those of the polymyxin B and positive control groups from 3 to 48 h; also, the concentrations of haptoglobin at different times in the polymyxin groups were lower than those of the positive control group and were significant at hours 3 to 48 (P < 0.05). Following the LPS administration, haptoglobin and TNF-α concentrations changed without significant difference between the two polymyxin B groups. Polymyxin B (6,000 U/kg) restrained blood lactate concentrations. Furthermore, it significantly improved the clinical signs in endotoxaemic animals, including rectal temperature and heart and respiratory rates. Polymyxin B may be an antiendotoxic in fat-tailed sheep.

Objective: To determine whether the method of lipopolysaccharide (LPS) administration (intermittent vs continuous) affects the magnitude and duration of the systemic inflammatory response in horses and whether prolonged (48 hours) endotoxemia induces laminitis. Animals: 12 healthy adult horses (10 mares and 2 geldings). Procedures: Horses were randomly assigned to receive LPS (total dose, 80 μg; n = 4) or saline (0.9% NaCl) solution (80 mL/h; 4) via constant rate infusion or 8 bolus IV injections of LPS (10 μg, q 6 h;4) during a 48-hour period. Physical examinations were performed every 4 hours, inflammatory cytokine gene expression was determined for blood samples obtained every 8 hours, and IV glucose tolerance tests were performed. Results: All LPS-treated horses had signs of depression and mild colic; those signs abated as the study progressed. Administration of LPS increased expression of interleukin-1β, interleukin-6, and interleukin-8, but results were not significantly different between LPS treatment groups. Cytokine expression was significantly higher on the first day versus the second day of LPS treatment. Interleukin-1β expression was positively correlated with rectal temperature and expression of other cytokines. Glucose and insulin dynamics for both LPS groups combined did not differ significantly from those of the saline solution group. Signs of laminitis were not detected in any of the horses. Conclusions and Clinical Relevance: Horses developed LPS tolerance within approximately 24 hours after administration was started, and the method of LPS administration did not affect the magnitude or duration of systemic inflammation. Laminitis was not induced in horses.

In this study, we investigated the kinetics of tumor necrosis factor (TNF)-α, interleukin (IL)-6 and high mobility group box 1 (HMGB1) concentrations in a 48-h model of canine endotoxemia by lipopolysaccharide (LPS) injection. Four healthy beagles were slowly administered 1 mg/kg of LPS diluted in normal saline, while two others were administered normal saline as controls. Blood collection was performed at 0 h (baseline), 1 h and 3 h (for TNF-α), 6 h, 12 h, 24 h and 48 h of the experiment, and cytokine levels were determined using the sandwich ELISA method. Early increments of TNF-α and IL-6 were observed (less than 3 h), but HMGB1 levels increased the most at 12 h of the experiment and gradually decreased until 48 h. During the whole experiment, IL-6 and HMGB1 were sustained over 12 h of LPS injection, whereas TNF-α decreased within 6 h of LPS injection. Taken together, canine HMGB1 levels increase relatively late (less than 12 h) and sustained longer than TNF-α and IL-6 in response to endotoxin. This is the first study to evaluate canine HMGB1 cytokine from endotoxemia in dogs.

The effect of mimicking prepartum concentration of estradiol-17 beta on the inflammatory response to endotoxin in gilts was studied. The study was performed in a split-litter design and comprised 5 pairs of littermates. A catheter was inserted into the jugular vein 2 days prior to the start of the study. In each pair, 1 littermate was treated IM with 2.5 mg of estradiol-17 beta/75 kg of body weight, and the other littermate was given peanut oil IM as a control. The day after treatment, all gilts were challenge-exposed with a Salmonella typhimurium-derived endotoxin (1 microgram/kg, IV) and the inflammatory response to challenge exposure was monitored. There was no effect of estradiol treatment on the transient clinical signs of endotoxemia or on the increase in rectal temperature. The increase in blood concentrations of prostaglandin F2 alpha, metabolite and cortisol after endotoxin challenge exposure was not affected by estradiol. Decrease in number of circulating blood mononuclear cells and polymorphonuclear leukocytes was not changed by estradiol treatment. Taken together, mimicking prepartum concentration of estradiol did not affect either the magnitude or the kinetics of the inflammatory response to endotoxin in gilts. Relevance of these findings to development of endotoxin-mediated diseases, such as the postpartum agalactia syndrome, needs further study.

Saline (0.9% NaCl) solution or 1 of 3 nonsteroidal anti-inflammatory drugs (NSAID) was administered IV to 5 neonatal calves 15 minutes after the start of a 3-hour IV infusion of Escherichia coli lipopolysaccharide (LPS; 2 micrograms/kg/h). Four additional calves were given a 3-hour IV infusion of saline solution alone. Clinical attitude, mean arterial blood pressure, PCV, WBC, and plasma lactate, glucose, and eicosanoid concentrations (thromboxane B2, 6-keto-PGF(1 alpha)) were monitored for 12 hours. Flunixin meglumine (1.1 mg/kg of body weight, IV), ketoprofen (2.2 mg/kg, IV), and ketorolac tromethamine (1.1 mg/kg, IV) each ameliorated the clinical signs of endotoxemia and LPS-induced lacticemia, but failed to significantly alter the degree of leukopenia or hypoglycemia associated with infusion of LPS. Although the 3 NSAID prevented eicosanoid production, they provided only partial protection against LPS-induced hypotension. Each NSAID modified the response to LPS, but none was clearly superior to the others in modulating the clinical signs or physiologic alterations induced by infusion of LPS in neonatal calves.

We evaluated the biochemical and hemodynamic response to hypertonic saline solution plus dextran in isoflurane-anesthetized pigs infused IV with Escherichia coli endotoxin (5 micrograms/kg of body weight for 0 to 1 hour + 2 micrograms/kg for 1 to 4 hours). After 120 minutes of endotoxemia, pigs were treated with a bolus (4 ml/kg over 3 minutes) of either normal saline solution (NSS; 0.9% NaCl), or hypertonic saline solution plus dextran (HSSD; 7.5% NaCl + 6% dextran-70). Administration of HSSD significantly (P < 0.05) increased serum osmolality and concentrations of sodium and chloride for approximately 2 hours during endotoxemia. Plasma total protein concentration decreased significantly (P < 0.05) for 2 hours after treatment with HSSD, indicating hemodilution and increased plasma volume. Although HSSD transiently increased cardiac index (CI) for approximately 15 minutes, this effect was not sustained; however, the endotoxin-induced decrease in CI was ameliorated from 120 to 180 minutes. In pigs of the endotoxin + NSS group from 180 to 240 minutes, CI decreased significantly (P < 0.05), compared with baseline and control values. The endotoxin-induced increases in mean pulmonary arterial pressure and pulmonary vascular resistance were not attenuated by HSSD. At 135 minutes, total peripheral vascular resistance was transiently lower (for approx 15 minutes) in pigs treated with HSSD, compared with control pigs. The endotoxin-induced increase in plasma lactate concentration was not attenuated by HSSD, indicating continued peripheral O2 debt. We conclude that, despite sustained increases in serum osmolality and concentrations of sodium and chloride, HSSD has only transiently beneficial cardiopulmonary effects during endotoxemia in pigs.

Objective—To evaluate the effects of clopidogrel on clinical and clinicopathologic variables in healthy horses with experimentally induced endotoxemia. Animals—12 adult mares. Procedures—Horses were assigned with a randomization procedure to receive clopidogrel (4 mg/kg, once, then 2 mg/kg, q 24 h; n = 6) or a placebo (6) through a nasogastric tube. After 72 hours of treatment, horses received lipopolysaccharide (LPS; 30 ng/kg, IV). Heart rate, respiratory rate, rectal temperature, CBC variables, plasma fibrinogen concentration, serum tumor necrosis factor-α concentration, plasma von Willebrand factor concentration, and measures of platelet activation (including ADP- and collagen-induced platelet aggregation and closure times, thrombelastography variables, and results of flow cytometric detection of platelet membrane P-selectin, phosphatidylserine, and microparticles) were determined at various times before and after LPS administration by investigators unaware of the treatment groups. Statistical analyses were performed with repeated-measures ANOVA. Results—4 of 6 clopidogrel-treated horses had significant decreases in ADP-induced platelet aggregation before and after LPS administration. Heart rate increased significantly after LPS administration only for the placebo group. No significant differences were detected between groups for CBC variables, closure time, and plasma concentration of fibrinogen or serum concentration of tumor necrosis factor-α, and no clinically relevant differences were detected for other hemostatic variables. Conclusions and Clinical Relevance—In this study, administration of LPS did not induce platelet hyperreactivity in horses on the basis of measures of platelet adhesion, aggregation, degranulation, and procoagulant activity. Administration of clopidogrel was associated with variable platelet antiaggregatory activity and attenuated some clinical signs of endotoxemia.

Objective-To test the hypothesis that inflammatory responses to endotoxemia differ between healthy horses and horses with equine metabolic syndrome (EMS). Animals-6 healthy horses and 6 horses with EMS. Procedures-Each horse randomly received an IV infusion of lipopolysaccharide (20 ng/kg [in 60 mL of sterile saline {0.9% NaCl} solution]) or saline solution, followed by the other treatment after a 7-day washout period. Baseline data were obtained 30 minutes before each infusion. After infusion, a physical examination was performed hourly for 9 hours and at 15 and 21 hours; a whole blood sample was collected at 30, 60, 90, 120, 180, and 240 minutes for assessment of inflammatory cytokine gene expression. Liver biopsy was performed between 240 and 360 minutes after infusion. Results-Following lipopolysaccharide infusion in healthy horses and horses with EMS, mean rectal temperature, heart rate, and respiratory rate increased, compared with baseline findings, as did whole blood gene expression of interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumor necrosis factor-α. The magnitude of blood cytokine responses did not differ between groups, but increased expression of IL-6, IL-8, IL-10, and tumor necrosis factor-α persisted for longer periods in EMS-affected horses. Lipopolysaccharide infusion increased liver tissue gene expressions of IL-6 in healthy horses and IL-8 in both healthy and EMS-affected horses, but these gene expressions did not differ between groups. Conclusions and Clinical Relevance-Results supported the hypothesis that EMS affects horses’ inflammatory responses to endotoxin by prolonging cytokine expression in circulating leukocytes. These findings are relevant to the association between obesity and laminitis in horses with EMS.

Objective-To test the hypothesis that glucose and insulin dynamics during endotoxemia differ between healthy horses and horses with equine metabolic syndrome (EMS). Animals-6 healthy adult mares and 6 horses with EMS. Procedures-Each horse randomly received an IV infusion of lipopolysaccharide (20 ng/kg [in 60 mL of sterile saline {0.9% NaCl} solution]) or saline solution, followed by the other treatment after a 7-day washout period. Baseline insulin-modified frequently sampled IV glucose tolerance tests were performed 27 hours before and then repeated at 0.5 and 21 hours after infusion. Results were assessed via minimal model analysis and area under the curve values for plasma glucose and serum insulin concentrations. Results-Lipopolysaccharide infusion decreased insulin sensitivity and increased area under the serum insulin concentration curve (treatment × time) in both healthy and EMS-affected horses, compared with findings following saline solution administration. The magnitude of increase in area under the plasma glucose curve following LPS administration was greater for the EMS-affected horses than it was for the healthy horses. Horses with EMS that received LPS or saline solution infusions had decreased insulin sensitivity over time. Conclusions and Clinical Relevance-Glucose and insulin responses to endotoxemia differed between healthy horses and horses with EMS, with greater loss of glycemic control in EMS-affected horses. Horses with EMS also had greater derangements in glucose and insulin homeostasis that were potentially stress induced. It may therefore be helpful to avoid exposure of these horses to stressful situations.

Objective: To determine the effectiveness of preinduction hyperbaric oxygen treatment (HBOT) in ameliorating signs of experimentally induced endotoxemia in horses. Animals: 18 healthy adult horses. Procedures: Horses were randomly assigned to 1 of 3 equal-sized treatment groups to receive normobaric ambient air and lipopolysaccharide (LPS), HBOT and LPS, or HBOT and physiologic saline (0.9% NaCl) solution. Horses were physically examined, and blood was obtained for a CBC and to determine concentration or activity of plasma tissue necrosis factor-α, blood lactate, and blood glucose before the horses were treated with HBOT and then intermittently for 6 hours after administration of LPS or physiologic saline solution. Results: All LPS-treated horses developed signs and biochemical and hematologic changes consistent with endotoxemia. Treatment with HBOT significantly ameliorated the effect of LPS on clinical endotoxemia score but did not significantly improve other abnormalities associated with endotoxemia. Conclusions and Clinical Relevance: The protective effect of HBOT was minimal, and results did not support its use as a treatment for horses prior to development of endotoxemia.