Abstract
A unique abnormality of osmoreceptors is reported in a child with hypothalamic hypopituitarism. Anterior pituitary testing revealed deficiency of GH, TSH and ACTH. The clinical course was characterized by fluctuation between dehydration of diabetes insipidus and coma of water intoxication. Plasma/Urine osmolality ranged from 263/110 mOsm/kg to 325/187 mOsm/kg. Osmotic threshold (OT) was determined by isovolemic infusion of hypertonic saline. An abrupt decrease of 30% or more of free water clearance defined the OT. During a hyponatremic episode the OT was detected at 263mOsm/kg. While hypernatremic OT was found at 300 mOsm/kg. These values are significantly different from the 286.6± 0.9 (M±SD) mOsm/kg found in 6 healthy volunteers. The presence of endogenous vasopressin, and the normally functioning volume receptors was demonstrated by the normal urine concentration when dehydrated. With plasma osmolality as high as 3O7mOsm/kg the child denied any feeling of thirst. The data indicate an instability of the osmoreceptors and a deficiency of thirst mechanism with intact volume receptors.
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