Since (i) chronic hypoxia is responsible for some PH forms, such as in PH associated with chronic obstructive pulmonary diseases (COPD) [41], and (ii) previous data in the literature showed that hypoxia is able to enhance NGF expression in other cell types [42], we also investigated whether hypoxia may alter NGF pulmonary arterial secretion. Here, NGF is linked to chronic obstructive pulmonary disease.