Plasma and urine nitric oxide concentrations in horses given a low dose of endotoxin

Aloisio C. Bueno From the Departments of Veterinary Clinical Sciences (Bueno, Seahorn, Cornick-Seahorn, Moore) and Veterinary Microbiology and Parasitology (Horohov), School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Thomas L. Seahorn From the Departments of Veterinary Clinical Sciences (Bueno, Seahorn, Cornick-Seahorn, Moore) and Veterinary Microbiology and Parasitology (Horohov), School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Janyce Cornick-Seahorn From the Departments of Veterinary Clinical Sciences (Bueno, Seahorn, Cornick-Seahorn, Moore) and Veterinary Microbiology and Parasitology (Horohov), School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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David W. Horohov From the Departments of Veterinary Clinical Sciences (Bueno, Seahorn, Cornick-Seahorn, Moore) and Veterinary Microbiology and Parasitology (Horohov), School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Rustin M. Moore From the Departments of Veterinary Clinical Sciences (Bueno, Seahorn, Cornick-Seahorn, Moore) and Veterinary Microbiology and Parasitology (Horohov), School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Abstract

Objective

To quantify plasma and urine nitric oxide (NO) concentrations before and after low-dose endotoxin infusion in horses.

Animals

11 healthy adult female horses.

Procedure

Eight horses were given endotoxin (35 ng/kg of body weight, IV) over 30 minutes. Three sentinel horses received an equivalent volume of saline (0.9% NaCl) solution over the same time. Clinical signs of disease and hemodynamic variables were recorded, and urine and plasma samples were obtained to measure NO concentrations prior to endotoxin infusion (t = 0) and every hour until postinfusion hour (PIH) 6, then every 2 hours until PIH 24. Blood for hematologic and metabolic analyses and for serum cytokine bioassays were collected at 0 hour, every hour until PIH 6, every 2 hours through PIH 12, and finally, every 6 hours until PIH 24.

Results

Differences in plasma NO concentrations across time were not apparent, but urine NO concentrations significantly decreased at 4 and 20 to 24 hours in endotoxin-treated horses. Also in endotoxin-treated horses, alterations in clinical signs of disease, and hemodymanic, metabolic, and hematologic variables were significant and characteristic of endotoxemia. Serum interleukin-6 (IL-6) activity and tumor necrosis factor (TNF) concentrations were increased above baseline values from 1 to 8 hours and 1 to 2 hours, respectively.

Conclusions and Clinical Relevance

Plasma and urine NO concentrations did not increase in horses after administration of a low dose of endotoxin, despite induction of an inflammatory response, which was confirmed by increased TNF and IL-6 values characteristic alterations in clinical signs of disease, and hematologic, hemodynamic and metabolic variables. (Am J Vet Res 1999:60:969-976)

Abstract

Objective

To quantify plasma and urine nitric oxide (NO) concentrations before and after low-dose endotoxin infusion in horses.

Animals

11 healthy adult female horses.

Procedure

Eight horses were given endotoxin (35 ng/kg of body weight, IV) over 30 minutes. Three sentinel horses received an equivalent volume of saline (0.9% NaCl) solution over the same time. Clinical signs of disease and hemodynamic variables were recorded, and urine and plasma samples were obtained to measure NO concentrations prior to endotoxin infusion (t = 0) and every hour until postinfusion hour (PIH) 6, then every 2 hours until PIH 24. Blood for hematologic and metabolic analyses and for serum cytokine bioassays were collected at 0 hour, every hour until PIH 6, every 2 hours through PIH 12, and finally, every 6 hours until PIH 24.

Results

Differences in plasma NO concentrations across time were not apparent, but urine NO concentrations significantly decreased at 4 and 20 to 24 hours in endotoxin-treated horses. Also in endotoxin-treated horses, alterations in clinical signs of disease, and hemodymanic, metabolic, and hematologic variables were significant and characteristic of endotoxemia. Serum interleukin-6 (IL-6) activity and tumor necrosis factor (TNF) concentrations were increased above baseline values from 1 to 8 hours and 1 to 2 hours, respectively.

Conclusions and Clinical Relevance

Plasma and urine NO concentrations did not increase in horses after administration of a low dose of endotoxin, despite induction of an inflammatory response, which was confirmed by increased TNF and IL-6 values characteristic alterations in clinical signs of disease, and hematologic, hemodynamic and metabolic variables. (Am J Vet Res 1999:60:969-976)

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