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  • Author or Editor: Natalie N. Norton x
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Abstract

Objective— To evaluate effects of polymyxin B sulfate (PMB) on response of horses to endotoxin, using an ex vivo model.

Animals—8 healthy horses.

Procedure—In a crossover design, 3 doses of PMB (100, 1,000, and 10,000 U/kg of body weight) and physiologic saline solution (control) were evaluated. Prior to and for 24 hours after administration of PMB, blood samples were collected into heparinized tubes for use in 2 assays. For the endotoxin-induced tumor necrosis factor (TNF) assay, blood samples were incubated (37 C for 4 h) with 1 ng of Escherichia coli or Salmonella Typhimurium endotoxin/ml of blood. Plasma was harvested and assayed. For the residual endotoxin activity assay, plasma was collected into sterile endotoxin-free borosilicate tubes, diluted 1:10 with pyrogen-free water, and incubated for 10 minutes at 70 C. Escherichia coli endotoxin (0.1 or 1 ng/ml of plasma) was added to the thawed samples prior to performing the limulus ameobocyte lysate assay. Serum creatinine concentrations were monitored for 1 week.

Results—Compared with baseline values, PMB caused a significant dose- and time- dependent decrease in endotoxin-induced TNF activity. Compared with baseline values, residual endotoxin activity was significantly reduced after administration of 10,000 U of PMB/kg. Compared with baseline values, 1,000 and 5,000 U of PMB/kg should inhibit 75% of endotoxin-induced TNF activity for 3 and 12 hours, respectively. Serum creatinine concentrations remained within the reference range.

Conclusion and Clinical Relevance—Results of the study suggest that PMB is a safe, effective inhibitor of endotoxin-induced inflammation in healthy horses. ( Am J Vet Res 2001; 62:72–76)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine which antimicrobials that are used to treat neonatal foals with septicemia attributable to Escherichia coli will minimize endotoxin release from bacteria and subsequent activity of inflammatory mediators while maintaining bactericidal efficacy.

Sample Population—Blood samples from 10 healthy foals.

ProcedureEscherichia coli isolates A and B were isolated from 2 septicemic foals, and minimal inhibitory concentrations (MIC) were determined for 9 antimicrobials. Five of these antimicrobials were tested in vitro at 2 and 20 times their respective MIC. Whole blood or mononuclear cells grown in tissue- culture media were incubated with 105 colonyforming units of E coli and each antimicrobial or saline (0.9% NaCl) solution. After 6 hours, number of viable bacteria remaining was determined, and supernatant was tested for endotoxin and tumor necrosis activity.

Results—Testing in whole blood was compromised by bactericidal effects of the blood itself. In mononuclear cell suspensions, each antimicrobial significantly reduced the number of viable bacteria to low or undetectable amounts. Antimicrobials did not differ significantly in efficacy of bacterial killing. Amikacin used alone or in combination with ampicillin resulted in significantly less endotoxin activity than did ampicillin, imipenem, or ceftiofur alone. There was a correlation between TNF-α and endotoxin activity.

Conclusions and Clinical Relevance—Aminoglycosides appear less likely to induce endotoxemia and TNF-α synthesis during bactericidal treatment of E coli septicemia, compared with β-lactam antimicrobials. Use of ampicillin, imipenem, or ceftiofur in the treatment of septicemic neonatal foals should be accompanied by appropriate treatment for endotoxemia. (Am J Vet Res 2002;63:660–668)

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate the effects of a standardized exercise test to exhaustion in horses on leukocyte function ex vivo.

Animals—6 Thoroughbred geldings.

Procedures—Blood samples were obtained from each horse before exercise; at exhaustion (termed failure); and at 2, 6, 24, 48, and 72 hours after exercise to evaluate hematologic changes, rate of leukocyte apoptosis, and leukocyte production of reactive oxygen species (ROS) ex vivo. To assess leukocyte function, leukocyte ROS production in response to stimulation with lipopolysaccharide, peptidoglycan, zymosan, and phorbol myristate acetate was evaluated. Apoptosis was evaluated via assessment of caspase activity in leukocyte lysates.

Results—In response to lipopolysaccharide, production of ROS by leukocytes was significantly increased at 2 hours and remained increased (albeit not significantly) at 6 hours after exercise, compared with the preexercise value. In the absence of any stimulus, leukocyte ROS production was significantly increased at 6 and 24 hours after exercise. In contrast, ROS production in response to phorbol myristate acetate was significantly decreased at 6, 24, and 72 hours after exercise. Leukocyte ROS production induced by zymosan or peptidoglycan was not altered by exercise. Leukocytosis was evident for 24 hours after exercise, and neutrophilia was detected during the first 6 hours. A significant increase in the rate of leukocyte apoptosis was detected at failure and 72 hours after exercise.

Conclusions and Clinical Relevance—Results indicated that strenuous exercise undertaken by horses causes alterations in innate immune system functions, some of which persist for as long as 72 hours after exercise.

Full access
in American Journal of Veterinary Research