Effect of BQ123 on vasoconstriction as a result of either hypoxia or endothelin‐1 in perfused rat lungs

A possible role of endothelin (ET)-1 in mediating hypoxic pulmonary vasoconstriction (HPV) was examined by comparing haemodynamic differences between ET-1-induced vasoconstriction and HPV in isolated perfused rat lungs. An ETA receptor antagonist (BQ123) was also employed to assess the effects of ET-1. The pulmonary arterial pressure (Ppa) was significantly increased by alveolar hypoxia (3% O2) and by ET-1 (5 nM). The pulmonary microvascular pressure was not changed by hypoxia, but increased more than two-fold by ET-1 (P < 0.01). Hypoxia significantly increased pulmonary arterial resistance (P < 0.01) while ET-1 significantly increased pulmonary venous resistance (P < 0.01), and slightly increased arterial resistance. Lung weight was increased by ET-1 and decreased by hypoxia, accompanied by similar Ppa responses in both cases. BQ123 (10(-6) M and 10(-5) M) did not influence the changes in Ppa and lung weight induced by hypoxia or angiotensin II (0.3 micrograms). BQ123 did, however, suppress (P < 0.05) the increase in Ppa and lung weight induced by 5 nM ET-1. Thus, it appears unlikely that ET-1 is involved in changes in pulmonary vascular tone during acute HPV.