Pulmonary and systemic effects of inhaled endotoxin in control and heaves horses

To investigate whether inhaled endotoxin contributes to airway inflammation and dysfunction in stabled horses, control (n = 6) and asymptomatic heaves (previously termed chronic obstructive pulmonary disease)-susceptible (n = 7) horses were given inhalation challenges with 20, 200 and 2000 mug of so luble Salmonella typhimurium Ra60 lipopolysaccharide (LPS), LPS inhalation induced a dose-dependent neutrophilic airway inflammatory response in both groups. Inhalation with 2000 mug of LPS also induced detectable lung dysfun ction in the heaves group, LPS inhalation did not alter clinical score, tra cheal secretion volume or airway reactivity in either group. The no-respons e thresholds were lower for the heaves group (< 20 mug for airway inflammat ion; 200 to 2000 mug for lung dysfunction) than for the control group (20 t o 200 mug for airway inflammation; > 2000 mug for lung dysfunction), To ena ble comparison of these threshold levels with airborne endotoxin concentrat ions in stables, horses also received a 5 h duration hay/straw challenge, d uring which the total and respirable airborne endotoxin concentrations were determined. Comparison of the effects of acute LPS inhalation and hay/stra w challenges suggest that inhaled endotoxin is not the sole cause of heaves , However, it is likely that it contributes to airway inflammation, both in heaves horses in concert with other inhalants, and in normal horses when t hey are exposed to high levels in poor stable environments.