Effects of a dual endothelin-I receptor antagonist on airway obstruction and acute lung injury in sheep following smoke inhalation and burn injury

Studies have suggested that ET-I (endothelin-I) is associated with lung injury, airway inflammation and increased vascular permeability. In the present study we have tested the hypothesis that treatment with a dual ET-I receptor antagonist will decrease airway obstruction and improve pulmonary function in sheep with combined S + B (smoke inhalation and burn) injury. Twelve sheep received S + B injury using the following protocol: six sheep were treated with tezosentan, an ET_A and ET_B receptor antagonist, and six sheep received an equivalent volume of vehicle. Physiological and morphological variables were assessed during the 48 h study period and at the end of the study. There was no statistically significant difference in the PaO ₂/FiO₂ (partial pressure of O₂ in arterial blood/fraction of O₂ in the inspired gas) ratio of the tezosentan-treated animals compared with controls; however, lung lymph flow was significantly higher (P < 0.05) in the treated animals. PVRI (pulmonary vascular resistance index) was significantly reduced (P < 0.05) in the tezosentan-treated animals. Assessment of NOx (nitric oxide metabolite) levels in plasma and lymph showed significantly elevated (P < 0.05) levels in the tezosentan-treated animals compared with levels in untreated sheep. The degree of bronchial obstruction was similar in both treated and control sheep; however, bronchiolar obstruction was reduced in sheep treated with tezosentan. Histopathologically, no difference in the degree of parenchymal injury was detected. In conclusion, administration of a dual ET-I receptor antagonist prevented an increase in PVRI after injury and reduced the degree of bronchiolar obstruction in sheep with S + B; however, treated sheep showed higher levels of NOx and increased lung lymph flow. Tezosentan treatment was ineffective in protecting against acute lung injury in this model.