Search Results

You are looking at 1 - 6 of 6 items for

  • Author or Editor: Natalie N. Norton x
  • Refine by Access: Content accessible to me x
Clear All Modify Search

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

SUMMARY

Objective

To evaluate the effect of pentoxifylline on response of horses to in vivo challenge exposure with endotoxin.

Animals

24 healthy horses in 3 treatment groups: pentoxifylline, endotoxin, or endotoxin and pentoxifylline.

Procedure

Horses of the pentoxifylline group were given a bolus of pentoxifylline (7.5 mg/kg of body weight, IV), followed by an infusion (3 mg/kg/h) over 3 hours, and those of the endotoxin group were given 20 ng of endotoxin/kg IV over 30 minutes. Those of the combination group were given both of the aforementioned compounds; pentoxifylline was administered immediately after endotoxin. Clinical (rectal temperature, heart and respiratory rates, blood pressure) and hematologic (WBC count; whole blood recalcification time; plasma fibrinogen, thromboxane B2, and 6-keto-prostaglandin F, concentrations; plasma plasminogen activator inhibitor activity; and serum tumor necrosis factor and interleukin 6 activities) variables were evaluated over 24 hours.

Results

Compared with baseline values, there were no significant changes in any variable over time in the horses receiving only pentoxifylline, with the exception of a significant increase in WBC count. Rectal temperature, heart rate, mean blood pressure, WBC count, whole blood recalcification time, fibrinogen concentration, plasminogen activator inhibitor activity, tumor necrosis factor and interleukin 6 activities, and plasma thromboxane B2 concentration changed significantly over time in horses of the endotoxin and endotoxin-pentoxifylline combination groups. Respiratory rate and plasma 6-keto-prostaglandin F concentration changed significantly over time only in horses of the endotoxin group. Compared with values for the endotoxin group, rectal temperature and respiratory rate were significantly lower, and whole blood recalcification time was longer for the endotoxin/pentoxifylline group.

Conclusion

Beneficial effects of pentoxifylline are limited when it is administered IV to horses after in vivo challenge exposure with endotoxin. (Am J Vet Res 1997;58:1300–1307)

Free access
in American Journal of Veterinary Research

SUMMARY

Objective

To compare effects of a single dose of pentoxifylline (PTX), flunixin meglumine (FM), and their combination (FM/PTX) in a model of equine endotoxemia.

Animals

24 healthy horses, aged 2 to 15 years.

Procedure

4 groups (n = 6/group) received 30 ng of Escherichia coli O55:B5 endotoxin/kg of body weight, IV, over 30 minutes, and 1 of the following preparations 15 minutes before and 8 hours after endotoxin infusion: FM, 1.1 mg/kg; PTX, 8 mg/kg; FM/PTX, 1.1 mg of FM and 8 mg of PTX/kg; and saline solution bolus (ENDO). Clinical and hematologic variables were measured over 24 hours.

Results

Compared with ENDO, FM given before endotoxin significantly reduced TxB2, and 6-keto-PGF1 concentrations, pulse, rectal temperature, and attitude score. Pentoxifylline given before endotoxin resulted in significantly higher 6-keto-PGF1 concentration at 1.5 hours and significantly lower PAI-1 activity at 12 hours. Tumor necrosis factor and IL-6 activities in horses given PTX alone were not significantly different from values in those given the saline bolus. FM/PTX induced effects similar to those of FM alone on endotoxin-induced changes in temperature and TxB2 concentration, and 6-keto-PGF1 concentration was significantly lower than that in horses of the ENDO group at 1 hour. In horses of the FM group, 6-keto-PGF1 concentration was significantly lower than that in horses of the ENDO group, from 0.5 hour to 2 hours. Horses of the FM and FM/PTX groups had significantly higher IL-6 activity at 1.5 and 2 hours than did horses of the PTX and ENDO groups; those of the FM and FM/PTX groups had significantly lower WBC count than did those of the PTX and ENDO groups.

Conclusions

FM/PTX may help offset deleterious hemodynamic effects of endotoxin more effectively than does either FM or PTX alone. (Am J Vet Res 1997;58:1291–1299)

Free access
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

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)

Full access
in American Journal of Veterinary Research

Abstract

Objective

To test efficacy of murine monoclonal, rabbit polyclonal recombinant equine or human tumor necrosis factor-α (rETNF or rHTNF, respectively) antibodies to inhibit native equine tumor necrosis factor (TNF) activity.

Animals

8 and 18 healthy adult horses for parts 1 and 2 of the study, respectively.

Procedures

In part 1, supernates from endotoxin-activated peritoneal macrophages were incubated with various dilutions of each rETNF antibody and subsequently tested for TNF activity. Serum was also obtained from a horse 1 hour after infusion with 20 ng of endotoxin/kg of body weight and was incubated with various dilutions of rabbit polyclonal rHTNF antibody. In part 2, 20 ng of endotoxin/kg was infused in horses during a 30-minute period. Fifteen minutes after the endotoxin infusion was initiated, 1 of 3 preparations was infused: 0.1 mg of rabbit polyclonal rHTNF antibody/kg, 0.1 mg of human IgG/kg, or 500 ml of 5% dextrose. Clinical and hematologic data were collected for 24 hours.

Results

Compared with the monoclonal antibody, the rabbit polyclonal rETNF antibody was more effective in inhibiting TNF activity. The 50% effective doses of the murine monoclonal rETNF, rabbit polyclonal rETNF, and rabbit rHTNF antibodies were 1.8, 0.8, and 0.6 μg of antibody/ml, respectively. In part 2, endotoxin infusion resulted in significant alternations in all variables; however, differences among treatment groups were not significant.

Conclusions and Clinical Relevance

Although murine monoclonal and rabbit polyclonal rETNF or rHTNF antibodies are capable of inhibiting native equine TNF activity in vitro, when given after initiation of endotoxemia, administration of 0.1 mg of rabbit polyclonal rHTNF/kg does not alter the response to infusion of endotoxin. (Am J Vet Res 1998;59:792-797)

Free access
in American Journal of Veterinary Research