Endothelin.

Endothelin (ET) belongs to a family of 21 amino acid peptides comprising at least three isoforms in man. Originally identified as an endothelium-derived vasoconstrictive substance, ET arises from a precursor peptide which is cleaved and released by a specific ET-converting enzyme. ET exerts multiple pharmacological effects through its own receptors. Among them, ET evokes the sustained and poorly reversible contraction of isolated vascular preparations and induces in vivo a long-lasting pressor effect preceded by transient hypotension. The mechanism of action of ET is not yet clarified although ET has been shown to stimulate phospholipase C and protein kinase C. It seems probable that this peptide acts more as a paracrine or autocrine signal than a circulating hormone. The availability of specific receptor antagonists and inhibitors of its biosynthesis will allow to understand the biological relevance of this novel family of peptides.