n. any one of a class of peptide hormones, consisting of chains of 21 amino acids, that are synthesized by endothelial cells, often of large blood vessels. They are the most powerful known stimulants of smooth muscle (such as that in the walls of arteries) and are believed to be important causes of hypertension. The drug bosentan, which blocks receptors for endothelin-1, is administered by mouth for the treatment of pulmonary hypertension.
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