Properties of [3H]l-Desamino-8-D-Arginine Vasopressin as a Radioligand for Vasopressin V2-Receptors in Rat Kidney

[3H]l-Desamino-8-D-arginine vasopressin [3H] DDAVP was assessed as a radioligand for vasopressin V2-receptors by studying its membrane-binding characteristics and in vitro autoradiographic localization in rat kidney, a rich source of V2-receptors. [3H]DDAVP bound specifically to a single class of high affinity, low capacity sites in rat medullopapillary membranes. Specific [3H]DDAVP binding at 25 C reached equilibrium after 2 h of incubation and was saturable and linear with protein concentration up to 2.2 mg/ml protein. Saturation analysis gave an equilibrium dissociation constant (Kd) of 0.76 nM. Displacement of [3H] DDAVP binding by unlabeled arginine vasopressin (AVP) and related analogs gave the following order of potency, consistent with that expected for a V2-receptor: DDAVP = AVP – 1-desamino-AVP > lysine vasopressin > oxytocin > [l-(β-mercapto-β,β-cyclopentamethylene-propionic acid, 2-(O-methyl)tyrosine]AVP. The C-terminal metabolites of AVP, (pGlu4Cyt6)AVP-(4–9), and (pGlu4Cyt6)AVP-(4–8) did not...