AVPR2 and Hyponatremia: AVP is an endogenous hormone (Figure 1a) that mediates antidiuretic effects on the kidney by signaling through three class A GPCR subtypes: V1a and V1b receptors activate phospholipases via Gq/11, while the V2R activates adenylyl cyclase by interacting with Gs (Birnbaumer, 2000) and is a therapeutic target for hyponatremia, hypertension, and incontinence (Ball, 2007).