Diabetes insipidus

Thirst is regulated in man and mammals by osmoreceptors in the supra-optic nuclei of the hypothalamus. An increase in plasma osmolality releases vasopressin from glandular neurones in these nuclei, which is then loosely bound to a carrier protein, neurophysin, and passes down the meons of the supra:opitico-hypophysial tract of the posterior lobe of the pituitary gland. Release of vasopressin also occurs, even if plasma osmolality is Iow, under the stimulus of pain, excitement, alpha-adrenergic agents, op~altes, hariblturates and niootline, and in smtes of rapid plasma or extra-cellular.. fluid loss, for example, haemorrhage and burns. Vasopressin release is inhibited by alcohol. Vasopressin, like its companion hormone oxytocin, is a. cyclic polypetide of 9 amino-acids. Man and most mammals produce arginine-vasopressin, the pig and the hippopotamus lysine-vasopressin. Vasopressin increases the permeability of the distal and collecting tubules of the renal nephron to water, thus potentiating water reabsorption. This action is mediated by cyclic 3: 5: adenosine-mono-phosphate which promotes active sodium ion transport across the cell membrane