Characterization of a novel non-peptide vasopressin V₁ receptor antagonist (OPC-21268) in the rat

A non-peptide, orally effective, vasopressin (AVP) V₁ receptor antagonist 1-{1-[4-(3-acetylaminopropoxy) benzoyl]-4-piperidyl}-3,4-dihydro-2(1H)-quinolinone (OPC-21268) has recently been described. This paper reports the in-vitro and in-vivo characterization of OPC-21268 binding to vasopressin receptors in rat liver and kidney. OPC-21268 caused a concentration-dependent displacement of the selective V₁ receptor antagonist radioligand, ¹²⁵I-labelled [d(CH₂)₅,sarcosine⁷]AVP to V₁ receptors in both rat liver and kidney medulla membranes. The concentration of OPC-21268 that displaced 50% of specific AVP binding (IC₅₀) was 40 ± 3 nmol/l for liver V₁ and 15 ± 2 nmol/l for kidney V₁ receptors (mean ± S.E.M.; n = 3). OPC-21268 had little effect on the selective V₂ antagonist radioligand [³H]desGly-NH₂⁹[d(CH₂)₅,D-Ile²,Ile⁴] AVP binding to V₂ receptors in renal medulla membranes (IC₅₀>0.1 mmol/l). After oral administration to rats, OPC-21268 was an effective V₁ antagonist in a time- and dose-dependent manner. Binding kinetic studies showed that OPC-21268 acted as a competitive antagonist at the liver V₁ receptor in vitro and in vivo, in addition to its in-vitro competitive effects at the renal V₁ receptor. OPC-21268 shows promise as an orally active V₁ antagonist.