Introduction: Endothelin-1(ET-1), a peptide of 21 amino acid residues, is the most potent vasoconstrictive substance known. Originally isolated from aortic endothelial cells, ET-1 is now known to be one of a family of three mammalian vasoactive peptides that also includes Endothelin-2 (ET-2) and Endothelin-3 (ET-3). These related peptides differ from ET-1 at two and six amino acid residue positions, respectively. A fourth peptide, vasoactive intestinal contractor (VIC), is sometimes classified a