ANTIDIURETIC AGENTS are used principally in the treatment of pituitary-originated (‘cranial’) diabetes insipidus, where they are used to counteract the underproduction of antidiuretic hormone (ADH; also called vasopressin), which is characteristic of this disease. This is a cyclic nonapeptide hormone secreted by the posterior pituitary gland, and occurs in mammals in two main forms. In most mammals including humans, the form is arginine vasopressin (argipressin), which can be used by injection. The porcine form is lysine vasopressin (lypressin; Lys8–vasopressin), which can be used in a nasal spray, as it can be absorbed by the nasal mucosa. Desmopressin is a synthetic analogue of arginine vasopressin that can be used as a nasal spray and by mouth. Terlipressin is a triglycyl derivative of lysine vasopressin, and can be used by injection (it is an inactive prodrug converted in vivo to lypressin). These are all (V subtype) VASOPRESSIN RECEPTOR AGONISTS, and the required antidiuretic activity is mediated principally at the V2-receptors of the kidney, rather than the V1-receptors that cause a vasopressor effect. See PITUITARY HORMONES.