The multifarious physiological effects of the neurohypophysial peptide hormones [arginine8]vasopressin (AVP) and oxytocin (OT) are mediated by a family of related G-protein-coupled receptors (GPRs). The V1a, V1b, and V2 subtypes of vasopressin receptor (VPR) and the oxytocin receptor (OTR) have now been cloned from several species. This has confirmed that although they are distinct proteins, they have related pharmacological characteristics and possess sequence homology. Identification of the domains/residues within these receptor proteins which give rise to the similarities/differences exhibited is of fundamental importance. With particular reference to the V1a receptor (V1aR) and the OTR, we have used a combination of site-directed mutagenesis, specific chemical modification and peptide mimetic approaches to investigate receptor:ligand interaction. In addition, the role of glycosylation of the extracellular loops of the rat V1aR has been addressed. This utilised a combination of site-directed mutagenesis and metabolic labelling in an in vitro translation system.
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