Endothelins are 21 amino acid peptides that are produced ubiquitously by vascular endothelial cells, smooth muscle cells, and other cells in different organs. Endothelins are secreted as big-endothelins that are converted to active proteins by the endothelin-converting enzyme. These peptides possess many biological activities, such as vasoconstriction and mitogenesis, and are involved in numerous physiological and pathophysiological processes in humans. Elevated plasma levels of endothelin have been associated with heart failure, and increased immunoreactivity for endothelin is observed in transplant coronary artery disease. Endothelin-1 (ET-1) is known as the most potent vasoconstrictor substance. For research use only, not for use in diagnostic procedures.