EDN1 and chronic obstructive pulmonary disease: Significant up-regulation of HIF-1α (COPD: 96.17 ± 30.88 pg/mL, COPD-PH: 119.29 ± 35.69 pg/mL, P < 0.001, Figure 1A) and ET-1 (COPD: 169.02 ± 40.21 pg/mL, COPD-PH: 224.73 ± 57.99 pg/mL, P < 0.001, Figure 1B) levels, and significant down-regulation of NO (COPD: 83.15 ± 22.94 μM, COPD-PH: 62.38 ± 19.70 μM, P < 0.001, Figure 1C) were revealed in the COPD-PH group.