BACKGROUND: The acute phase response is beneficial to the
animal in restoring homeostasis, and measuring the circulating
acute phase proteins, cytokines, and enzymes can be used to
evaluate the innate immune system's responses to invader agents
such as bacterial lipopolysaccharide. Measurement of these
parameters has shown to be useful as diagnostic and prognostic
markers in animal endotoxemia. OBJECTIVES: The aim of the
present experimental study was expression of the acute phase
response following the induction of endotoxemia by Escherichia
coli serotype O55:B5 in sheep and the relationships among the acute
phase response parameters during endotoxemia and their changing
patterns. METHODS: Five clinically healthy 1-year-old Iranian fattailed
ewes (25±1.5 kg, bodyweight) were randomly selected and
lipopolysaccharide from Escherichia coli serotype O55:B5 was
infused at 20 μg/kg intravenously to each animal. Fluid therapy was
performed in all ewes over 120 minutes after lipopolysaccharide
injection and continued for 180 minutes. Blood samples were
collected from all ewes prior and 1, 2, 3, 4, 5, 6, and 24 hours after
lipopolysaccharide injection and sera were separated. Serum
concentrations of haptoglobin, serum amyloid A, tumor necrosis
factor-alpha, interferon-gamma, superoxide dismutase, and
glutathione peroxidase were assayed. RESULTS: The rapid and
significant elevation of haptoglobin, serum amyloid A, tumor
necrosis factor-alpha, and interferon-gamma were seen after
endotoxemia induction. Serum concentrations of superoxide
dismutase and glutathione peroxidase were significantly decreased
after intravenous lipopolysaccharide infusion. The results of the
present experimental study showed that haptoglobin, serum
amyloid A, tumor necrosis factor-alpha, and interferon-gamma at
all hours studied after endotoxemia induction were positively
correlated together. These parameters were negatively correlated
with superoxide dismutase and glutathione peroxidase at all hours
after lipopolysaccharide infusion. CONCLUSIONS: The results of
the present experiment can provide evidence for associations
among acute phase proteins, cytokines, and enzymes and their
changes during endotoxemia in sheep.