AVPR2 and Hyponatremia: Muta et al. (1989) showed that 1 mM chlorpropamide reduced AVP binding to the V2R within the rat renal tubular basolateral membrane in a competitive manner, indicating that chlorpropamide acts on the V2R (Muta et al., 1989). Using a radioiodinated derivative of AVP with high specific activity and high affinity for the V2R, Hensen et al. (1995) showed that low-dose oral chlorpropamide increased the V2R density without altering plasma AVP concentrations (Hensen et al., 1995); the V2R upregulation was therefore postulated to underlie chlorpropamide-induced hyponatremia.