The big endothelins comprise residues 53-90 (human big ET-1) and 53-91 (porcine big ET-1) of the endothelin precursor (preproendothelin). Compared to the mature endothelin-1 (ET-1), both peptides show less vasoconstrictor activity in vitro, but similar pressor effects in vivo. Former CAS-number 121014-54-8.