Syndrome of Inappropriate Secretion of Antidiuretic Hormone

Abstract

Antidiuretic hormone (ADH) plays a prominent role in the control of volume and osmotic homeostasis. ADH, or arginine vasopressin, is secreted in the hypothalamus, travels down the hypothalamic-hypophysial tract coupled to a protein called neurophysin, and is stored in the posterior aspect of the hypophysis. From there, it eventually is liberated in the blood stream. The changes occurring in osmolality or volume are sensed by intracranial osmoreceptors and pressure or volume receptors located at the carotid and aortic sinuses, and left atrium, respectively. Once vasopressin enters the circulation, it follows a course to its specific receptor site on the contraluminal (blood) side of the collecting duct cells of the kidney where it initiates a chain of intracellular events through activation of cyclic AMP. This reaction brings about a striking increase in the luminal cell membrane permeability to water, urea, sodium and other solutes (1).These biochemical events may be inhibited or enhanced by a host of circumstances and might lead to derangements in body fluids.