Endothelins are peptides with receptors and effects in many body organs. Endothelin constricts blood vessels and raises blood pressure. The endothelins are normally kept in balance by other mechanisms, but when overexpressed, they contribute to high blood pressure (hypertension), heart disease, and potentially other diseases. Endothelins are 21-amino acid vasoconstricting peptides produced primarily in the endothelium having a key role in vascular homeostasis. Endothelins are implicated in vascular diseases of several organ systems, including the heart, lungs, kidneys, and brain. As of 2018, endothelins remain under extensive basic and clinical research to define their roles in several organ systems. Etymology Endothelins derived the name from their isolation in cultured endothelial cells. Isoforms There are three isoforms of the peptide (identified as ET-1, -2, -3), each encoded by a separate gene, with varying regions of expression and binding to at least four known endothelin receptors, ETA, ETB1, ETB2 and ETC. The human genes for endothelin-1 (ET-1), endothelin-2 (ET-2), and endothelin-3 (ET-3) are located on chromosomes 6, 1, and 20, respectively. Mechanism of action and function Endothelin functions through activation of two G protein-coupled receptors, endothelinA and endothelinB receptor (ETA and ETB, respectively). These two subtypes of endothelin receptor are distinguished in the laboratory by the order of their affinity for the three endothelin peptides: the ETA receptor is selective for ET-1, whereas the ETB receptor has the same affinity for all three ET peptides. The two types of ET receptor are distributed across diverse cells and organs, but with different levels of expression and activity, indicating a multiple-organ ET system. Most endothelin receptors in the human cerebral cortex (~90%) are of the ETB subtype. Endothelin-1 is the most powerful endogenous chemical affecting vascular tone across organ systems. Secretion of endothelin-1 from the vascular endothelium signals vasoconstriction and influences local cellular growth and survival. ET-1 has been implicated in the development and progression of several cardiovascular diseases, such as atherosclerosis and hypertension. Endothelin also has roles in mitogenesis, cell survival, angiogenesis, bone growth, nociceptor function, and cancer onset mechanisms. Clinically, anti-ET drugs are used to treat pulmonary arterial hypertension. Endothelin-2 differs from endothelin-1 by two amino acids, and sometimes has the same affinity as endothelin-1 for ETA and ETB receptors. Studies have shown that endothelin-2 plays a significant role in ovarian physiology and could impact the pathophysiology of heart failure, immunology, and cancer. Physiological effects Endothelins are the most potent vasoconstrictors known.