The synthesis and secretion of endothelin in patients with COPD increase,106 and during the exacerbation of COPD, the level of endothelin further rises and participates in the formation of pulmonary hypertension.107,108 ET-1 can also stimulate the liver to produce more C-reactive protein (CRP) by up-regulating IL-6. Here, IL6 is linked to chronic obstructive pulmonary disease.