Urotensin-II (UT) receptor ligand; behaves as a silent antagonist in most in vitro assays and in vivo, but does retain small residual agonist activity under certain conditions in some assays. Competitively antagonizes U-II induced contractions in the rat aorta (pIC50 = 7.46) and prevents plasma extravasation elicited by U-II in mice in vivo. MW (observed): 1061.24.