Endothelins (ET) show potent constrictor activity in vascular and non-vascular smooth muscle. This family of 21-amino acid peptides exists in at least three isoforms - ET-1, ET-2, and ET-3, and is produced in endothelial and epithelial cells. ET's can mediate biological effects in cells and tissues, and have been shown to bind to an ET receptor in the lung, kidney, heart, and liver. Endothelin 1 is expressed in lung, placental stem villi vessels and in cultured placental vascular smoot