EDN1 and Hypertension: 35Thus, in general, it was the more severe forms of experimental hypertension that exhibited enhanced ET-1 expression and responded to ETRA with lowering of BP. Together with enhanced vascular tone in hypertensive humans [32] and exaggerated expression of ET-1 in the endothelium of small arteries in humans with uncontrolled hypertension [33], this suggested that hypertensive patients with difficult-to-control hypertension would be prime candidates for treatment with ETRA.