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

Objective-To quantify plasma and urine nitric oxide (NO) concentrations bef ore 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) o ver 30 minutes. Three sentinel horses received an equivalent volume of sali ne (0.9% NaCl) solution over the same time. Clinical signs of disease and h emodynamic variables were recorded, and urine and plasma samples were obtai ned to measure NO concentrations prior to endotoxin infusion (t = 0) and ev ery hour until postinfusion hour (PIH) 6, then every 2 hours until PIH 24. Blood for hematologic and metabolic analyses and for serum cytokine bioassa ys 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 appare nt, but urine NO concentrations significantly decreased at 4 and 20 to 24 h ours in endotoxin-treated horses. Also in endotoxin-treated horses, alterat ions in clinical signs of disease, and hemodymanic, metabolic, and hematolo gic variables were significant and characteristic of endotoxemia. Serum int erleukin-6 (IL-6) activity and tumor necrosis factor (TNF) concentrations w ere increased above baseline values from 1 to 8 hours and 1 to 2 hours, res pectively. Conclusions and Clinical Relevance-Plasma and urine NO concentrations did n ot increase in horses after administration of a low dose of endotoxin, desp ite induction of an inflammatory response, which was confirmed by increased TNF and IL-6 values characteristic alterations in clinical signs of diseas e, and hematologic, hemodynamic and metabolic variables.