EDN1 and cyclic hematopoiesis: The major findings of this study are as follows: (1) mtROS contribute to the progression of CH-induced PH, right ventricular hypertrophy, and pulmonary arterial remodeling; (2) CH increases mtROS levels in PASMCs independent of endothelial influences, leading to enhanced basal arterial tone; (3) the endothelium markedly potentiates mtROS-dependent increases in arterial tone following CH; and (4) this effect of the endothelium is mediated by ET-1-induced stimulation of PASMC mtROS production.