Effect of the endothelin receptor antagonist SB217242 on hypoxic vasodilation. (A) Effect of the endothelin receptor antagonist SB217242 (10 μM) on concentration-response curves for oxygen (O2) lowering in coronary arterial segments with and without endothelium contracted with PGF2α (10 μM). (B) Tissue ET-1 in arteries exposed to 1 h of hypoxia (5% CO2, 95% N2) compared to normoxic controls. By adding ET-1 (10-7 M) to the organ bath we were able to measure ET-1 (P < 0.001). (C) Concentration-response curves for increasing concentrations of ET-1 in coronary artery segments with and without endothelium and constricted with PGF2α (10 μM) and subsequently exposed to 1% O2 or 95% O2 for 30 min as well as during the rest of the experiments. Results are means ± SEM of 4-9 experiments. Differences were evaluated with two-way ANOVA followed by Bonferroni post-test: * P < 0.05, ** P < 0.01, ***P < 0.001 compared to control.