A hormone, secreted by the posterior pituitary gland, that stimulates reabsorption of water by the kidneys and thus controls the concentration of body fluids (i.e. osmolarity) and also blood pressure. ADH is produced by specialized nerve cells in the hypothalamus of the brain and is transported to the posterior pituitary in the bloodstream. Secretion is stimulated by signals from osmoreceptors in the hypothalamus, which detect increased osmolarity, and inhibited by signals from baroreceptors in the great arteries, which detect increases in blood pressure. ADH causes increased insertion of aquaporins in the collecting ducts of the kidneys, thereby allowing more water to pass from the collecting duct fluid into the renal medulla. Deficiency of ADH results in a disorder known as diabetes insipidus, in which large volumes of urine are excreted; it is treated by administration of natural or synthetic hormone. See also neurophysin.