Abstract： Background It has been shown that neurohumoral factors other than mechanical obstruction are involved in the pathophysiology of acute pulmonary thromboembolism (APTE). The aim of this study was to investigate the effects of thrombolytic drugs, a selective endothelin-1 receptor (ET-1R) antagonist alone or their combination on APTE in a canine model.Methods Twenty dogs were randomly assigned to five groups: sham, model, urokinase (UK), BQ123, and combination (UK plus BQ123). The dogs in the sham group underwent sham surgery. APTE was induced in the other four groups by intravenous injection of autologous blood clots. Dogs in the UK, BQ123 and combination groups received UK, BQ123 (a selective ET-1R antagonist), or UK plus BQ123, respectively. The dogs in the model group were given saline. Mean pulmonary artery pressure (mPAP), serum concentrations of ET-1, thromboxane (TXB2), and tumor necrosis factor (TNF)-α were determined at different time points following the induction of APTE.Results UK and BQ123 alone markedly decreased mPAP in APTE. By comparison, the reduction was more significant in the combination group. Compared with the sham group ((-0.90±0.61) mmHg), mPAP increased by (7.44±1.04), (3.42±1.12) and (1.14±0.55) mmHg in the model group, UK alone and BQ123 alone groups, respectively, and decreased by (2.24±0.67) mmHg in the combination group (P <0.01). Serum ET-1 concentrations in the BQ123 and combination groups were (52.95±8.53) and (74.42±10.27) pg/ml, respectively, and were significantly lower than those in the model and UK groups ((84.56±7.44) and (97.66±8.31) pg/ml respectively; P <0.01). Serum TNF-α concentrations were significantly lower in the BQ123 group than in the model, UK and combination groups (P <0.05).Conclusions Our results indicate that the selective ET-1R antagonist BQ123 not only reduces the increase of mPAP and serum ET-1 level, but also inhibits the production of TNF-α, and attenuates the local inflammatory response induced by APTE. Selective ET-1R antagonists may be beneficial to the treatment of APTE, particularly when used in combination with a thrombolytic agent.