Diabetes Insipidus

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Diabetes insipidus is an uncommon form of diabetes which results either from a failure of the pituitary gland to secrete enough antidiuretic hormone (ADH) or a failure of the kidneys to respond to ADH. The main symptoms are excessive thirst and the passing of large quantities of dilute urine. If water is unobtainable or witheld, the affected person becomes dehydrated and will eventually become comatose. The condition is treated by giving analogues of ADH such as lypressin or desmopressin.

ADH is a small peptide – formed from only 9 amino acids. It is synthesised in the hypothalamus and released from the posterior lobe of the pituitary. The output of ADH is influenced by the osmolarity of the blood and information coming to the hypothalamus from baroreceptors monitoring blood pressure. ADH increases the permeability of the collecting ducts in the kidney to water and urea. It also stimulates the active resoption of sodium chloride by the ascending limb of the loop of Henle and the collecting ducts. The production of ADH is linked with the neurological processes involved in thirst.

Diabetes insipidus can be inherited, but this is rare. Usually it is caused by head injuries, brain tumours, or infections of the brain.

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