[Hypodypsia and selective dysfunction of osmoreceptors in the hypernatremia syndrome]

We studied a patient with the rare syndrome of chronic hypernatremia associated with a frontal expansive process. The pituitary function was evaluated during dynamic tests bearing on radioimmunoassay of serum neurophysins levels. A test of water restrictionloading was performed during which urine appeared diluted (190-200 mOsm/kg) while the degree of serum osmolality was high (310-317 mOsm/kg). An hemodynamic stimulation resulted in a significant increase in serum neurophysins (from 3.5 +/- 0.3 to 5.5 +/- 0.2 ng/ml). After one intravenous injection of 2 mg nicotine, vomiting was observed, followed by a sharp rising of serum neurophysins levels (from 3.2 +/- 0.5 to 10.6 +/- 0.2 ng/ml). During hypertonic saline infusion, serum osmolality increased from 270 to 310 mOsm/kg, while neurophysins showed no significant change. Such results evidence a selective impairment of the hypothalamic-neurohypophyseal response to osmotic stimuli, with intact mechanisms of non-osmotic stimulation. In this patient, natremia was brought back to normal values by adequate water supply.