Endothelin 1 (ET-1), also known as preproendothelin-1 (PPET1), is a potent vasoconstrictor that in humans is encoded by the EDN1 gene and produced by vascular endothelial cells. The protein encoded by this gene is proteolytically processed to release a secreted peptide termed endothelin 1. Endothelin 1 is one of three isoforms of human endothelin.