DIABETES INSIPIDUS

pathological endocrine condition characterized by extreme thirst and excessive production of very dilute urine. The essential feature of the disorder appears to be a lack of antidiuretic hormone (vasopressin) or a blocking of its action. This hormone, produced by the hypothalamus, regulates the kidney's conservation of water and production of urine. The causes may be numerous: failure of osmoreceptors; tumours; inflammation of the hypothalamus or posterior pituitary lobe (neurohypophysis) by such diseases as syphilis or meningitis; granulomas; trauma, such as skull fracture or concussion; lesions; or failure of the tubules to respond to antidiuretic hormone. The form of the disorder that results from injury to the hypothalamic nucleus, which is the tract by which vasopressin is conveyed to the neurohypophysis for storage, is called supraoptic hypophyseal diabetes insipidus, or SHDI. Nephrogenic diabetes insipidus (NDI) results when the supplies of vasopressin are adequate but the kidney tubules are unresponsiveeither genetically or because of potassium depletion, high levels of serum calcium, or other disorders. SHDI can be alleviated by injections of vasopressin-like compounds of animal or synthetic origin; such treatment, however, is ineffective for NDI.