Arginine vasopressin
Mechanism of action of arginine vasopressin (AVP) on the epithelial cells of the late distal tubules, collecting tubules, and collecting ducts. AVP binds to its V2 receptors, which are coupled with stimulatory G proteins (Gs) that activate adenylate cyclase (AC) and stimulate formation of cyclic adenosine monophosphate (cAMP). This, in turn, activates protein kinase A and phosphorylation of intracellular proteins, causing movement of aquaporin-2 (AQP-2) to the luminal side of the cell membrane. The molecules of AQP-2 fuse together to form water channels. On the basolateral side of the cell membrane are other aquaporins, AQP-3 and AQP-4, that permit water to flow out of the cell, although these aquaporins do not appear to be regulated by AVP.