PROPERTIES OF A NEW RADIOIODINATED ANTAGONIST FOR HUMAN VASOPRESSIN V-2 AND V-1A RECEPTORS

A vasopressin receptor antagonist, 1-(beta-mercapto-beta,beta-pentamet hylenepropionic acid), 2-O-ethyl-D-tyrosine, 4-valine, 9-tyrosylamide] arginine vasopressin (d(CH2)(5)[o-ethyl-D-Tyr(2),Tyr-NH29]AVP), has b een prepared. This antagonist is a potent antiantidiuretic, antivasopr essor and antioxytocic peptide with pA(2) values of 7.69-7.94 and affi nities of 1.12-11.0 nM. When radioiodinated at the phenyl moiety of th e tyrosylamide residue at position 9, this peptide was demonstrated to bind to vasopressin V-2 and V-1a receptors with a dissociation consta nt 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.