Properties of a new radioiodinated antagonist for human vasopressin V-2 and V-1a receptors

A vasopressin receptor antagonist, [1-(beta-mercapto-beta,beta-pentamethylenepropionic acid), 2-O-ethyl-D-tyrosine, 4-valine, 9-tyrosylamide] arginine vasopressin (d(CH2)(5)[o-ethyl-D-Tyr(2),Tyr-NH29]AVP), has been prepared. This antagonist is a potent antiantidiuretic, antivasopressor and antioxytocic peptide with pA(2) values of 7.69-7.94 and affinities of 1.12-11.0 nM. When radioiodinated at the phenyl moiety of the tyrosylamide residue at position 9, this peptide was demonstrated to bind to vasopressin V-2 and V-1a receptors with a dissociation constant of 0.22-0.75 nM. This ligand is a good tool for further studies on human vasopressin V, receptor localization and characterization, when used in combination with a selective vasopressin V-1a ligand. (C) 1997 Elsevier Science B.V.