18 – Vla Vasopressin Receptors: Studies with Radioiodinated Ligand

Publisher Summary The nonapeptides [Arg 8 ]vasopressin (AVP) and oxytocin (OT) are closely related members of a hormone family that differ by only two amino acids. They are derived from the same ancestral gene and are secreted from the posterior pituitary of male and female mammals. Receptors for vasopressin and OT have been characterized in a large number of tissues and cell types. It has been proposed that a functional criterion can be used to distinguish two vasopressin receptor subtypes, V 1 and V 2 . Receptors of the V 2 type were defined as the renal adenylate cyclase-coupled receptors involved in the antidiuretic effect of vasopressin. Receptors of the V 1a type were defined as the receptors present in hepatocytes that mediate increased inositol lipid turnover and cause a rise in cytosolic calcium. Receptors of the V 1b type are the receptors that are present in the adenohypophysis, have a low affinity for vasopressin antagonists, and are coupled to an inositol lipid turnover. OT receptor-mediated stimulation of inositol phosphates has been demonstrated in the myometrium from several mammalian species, indicating that OT receptors and vasopressin receptors of the V 1 subtype exhibit functional similarities.