1. A 21-amino acid peptide originally derived from endothelial cells. It is an extremely potent vasoconstrictor. Three different gene products have been identified, endothelin 1, endothelin 2, and endothelin 3; they are found in brain, kidney, and endothelium (endothelin 1), intestine (endothelin 2), and intestine and adrenal gland (endothelin 3).
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