Kinase experiment:

To determine binding kinetic constants, liver or kidney plasma membranes are incubated with increasing concentrations of [3H]-AVP with or without excess (1 μM) unlabelled AVP to obtain a saturation curve. To investigate whether mozavaptan interacts competitively or noncompetitively, the saturation binding of [3H]-AVP is examined in the absence and presence of mozavaptan at concentrations of 0.3 μM and 1 μM in liver membranes and 3 nM, and 10 nM in kidney membranes. Data on the saturation curve are plotted according to the method of Scatchard and fitted by a regression analysis[1].

Animal experiment:

Rats: Mozavaptan is dissolved in DMSO at a concentration of 10 mM and diluted with assay buffer. Female Brattleboro rats homozygous for hypothalamic diabetes insipidus and weighing between 180 and 280g are used. Mozavaptan (30 mg/kg) and vehicle (5% gum arabic) are administered orally in a volume of 2 mL/kg and d(CH2)5Tyr(Et)VAVP (10pgkg-1) is administered in a volume of 1 mL/kg. Spontaneously voided urine is collected for 6h with metabolic cages. Both before and during the study, the rats received water and food ad libitum[1].

Mozavaptan (OPC31260) is a orally effective, nonpeptide vasopressin V2 receptor antagonist with an IC50 of 14 nM.

Mozavaptan causes a competitive displacement of [3H]-arginine vasopressin (AVP) binding to both V1 and V2 receptors with IC50 values of 1.2 μM and 14 nM, respectively. The Kd of [3H]-AVP is reduced significantly in both rat liver and kidney in the presence of mozavaptan (Kd=1.1 nM in liver, Kd=1.38 nM in kidney)[1].

Mozavaptan at doses of 10 to 100 μg/kg, i.v., inhibits the antidiuretic action of exogenously administered arginine vasopressin in water-loaded, alcohol-anaesthetized rats in a dose-dependent manner. Mozavaptan does not exert an antidiuretic activity suggesting that it is not a partial V2 receptor agonist. Mozavaptan dose-dependently increases urine flow and decreases urine osmolality after oral administration at doses of 1 to 30 mg/kg in normal conscious rats[1].

References:
[1]. Yamamura Y, et al. Characterization of a novel aquaretic agent, OPC-31260, as an orally effective, nonpeptide vasopressin V2 receptor antagonist. Br J Pharmacol. 1992 Apr;105(4):787-91.