Pathogenesis of chronic hypernatremia with dehydrated and non-dehydrated states in hypothalamic space-occupying lesions.

The present study was undertaken to determine pathophysiology of body water control in hypernatremic subjects with hypothalamic space-occupying lesions. Eight subjects with hypothalamic space-occupying lesions were divided into two groups of hypernatremia in the presence or absence of body water deficit. In 5 dehydrated hypernatremic subjects whose ages ranged from 20 to 67 years, serum sodium (Na) levels were 156.4 +/- 3.1 mmol/l; plasma osmolality (Posm), 320.6 +/- 9.8 mmol/kg; and urinary osmolality (Uosm), 246.8 +/- 46.7 mmol/kg under ad libitum water drinking. In 3 non-dehydrated hypernatremic subjects whose ages ranged from 21 to 32 years, serum Na levels were 150.3 +/- 5.4 mmol/l; Posm, 300.3 +/- 11.6 mmol/kg; and Uosm, 738.7 +/- 237.1 mmol/kg. Serum Na levels had a positive correlation with hematocrit (Ht) in 2 of 5 subjects with dehydration, but it totally disappeared in the 3 subjects without dehydration. Plasma arginine vasopressin (AVP) levels were 0.7 +/- 0.1 pmol/l, and there was no response of AVP release to intravenous administration of 5% NaCl in the subjects with dehydration. Plasma AVP was 0.7 +/- 0.1 pmol/l, and there was the reduced response of AVP release to 5% NaCl in those without dehydration. In one of 3 subjects a positive correlation between Posm and plasma AVP levels was obtained. Drinking behavior was totally abolished in the subjects with dehydration, and partly reduced in those without dehydration. The present study indicates that hypothalamic space-occupying lesions causes central diabetes insipidus and hypodipsia, and that sporadic and paradoxical release of AVP, enhanced renal concentrating ability and reduced drinking behavior may possess body water minimally in the hypernatremic subjects without water deficit.