EDN1 and endothelial dysfunction: 2007). In CIH rats, circulating ET‐1 levels and the sensitivity of the vasoconstrictor response to ET‐1 were also increased (Kanagy et al. 2001; Brunner et al. 2006). Moreover, previous studies have shown that ET‐1 and ET receptors play a key role in CIH‐induced endothelial dysfunction and augmented vasoconstriction of aortas and pulmonary arteries in rats (Guo et al. 2013; Wang et al. 2013).