Defects in osmoregulation of vasopressin secretion. A report of four cases

Neural Substrate Essential for Suppression of Vasopressin Secretion and Excretion of a Water Load

Suppression of vasopressin secretion to very low levels is essential for the excretion of excess water. To investigate a role for the preoptic brain region in the suppression of vasopressin secretion and the excretion of a water load, lesions were made in the vicinity of the lamina terminalis in ewes (LTX-sheep) and responses to water-loading or reduction of cerebrospinal fluid NaCl by i.c.v. isotonic mannitol solution were investigated. In normal conscious sheep, intraruminal water-loading resulted in the urine flow rate increasing and urine osmolality decreasing within 1 h, such that renal free water clearance (CH 2O ) increased from -1.02 ± 0.16 ml/min (mean ± SEM) to a maximum of +4.99 ± 0.62 ml/min at 2.5 h after water-loading (P < 0.05, n = 6). Plasma vasopressin levels fell from 0.88 ± 0.17 pg/ml to undetectable levels (< 0.4 pg/ml, n = 4). In LTX-sheep (n = 6), CH 2O did not change significantly after water-loading (-1.78 ± 0.13 to -2.03 ± 0.49 ml/min at 2.5 h after water-loading). Plasma vasopressin levels were inappropriately elevated in water-loaded LTX-sheep (n = 3). Intracerebroventricular mannitol (1 ml/h for 2 h) resulted in a water diuresis and increase in CH 2O (-1.16 ± 0.12 to +2.81 ± 0.58 ml/min, P < 0.05) after 2 h in normal sheep, and plasma vasopressin levels fell significantly from to 0.88 ± 0.23 pg/ml to < 0.4 pg/ml (P < 0.05, n = 6). However, in LTX-sheep, there was no change in CH 2O (-1.31 ± 0.14 to -1.35 ± 0.12 ml/min) or the plasma vasopressin concentration (1.47 ± 0.18 to 1.60 ± 0.44 pg/ml, not significant) with i.c.v. mannitol. The results suggest that an inhibitory pathway from the vicinity of the median preoptic nucleus to the supraoptic and hypothalamic paraventricular nuclei plays an important role in the suppression of vasopressin secretion and the excretion of excess water.

24-hour cerebrospinal fluid levels of vasopressin in hydrocephalic patients

The variation in vasopressin concentrations of ventricular cerebrospinal fluid and plasma throughout a 24-h period was studied in 10 patients with hydrocephalus. In 6 control patients, the diurnal variation in plasma vasopressin concentrations was studied. Vasopressin concentrations were determined by radioimmunoassay in plasma and in extracted and unextracted cerebrospinal fluid. Cortisol and osmolality in plasma were also measured. Vasopressin concentrations measured in extracted cerebrospinal fluid showed only small intra- and interindividual variation, while the corresponding values for unextracted cerebrospinal fluid were 2-5-fold higher and showed more variation. Plasma vasopressin concentrations varied considerably throughout the 24-h period in the individual hydrocephalic patient and between the patients. The pattern of variation was inconstant with no circadian rhythm, and the variation was not related to any changes in plasma osmolality, blood pressure or intracranial pressure. In some of the patients, the normal diurnal pattern of variation in plasma cortisol was broken, however, without a relation to the observed fluctuations in vasopressin concentrations. The abnormal variation of plasma vasopressin and cortisol was considered to reflect stress in connection with the intracranial pressure monitoring procedure. In the control patients, plasma vasopressin showed only small variations and plasma cortisol showed a normal diurnal rhythm. It is concluded that cerebrospinal fluid vasopressin concentration in patients with hydrocephalus is very constant throughout the day, even when plasma vasopressin concentrations show marked episodic increases. Thus, a circadian rhythm in the cerebrospinal fluid vasopressin concentration, as reported in several animal species, could not be confirmed in these patients.

CSF and plasma vasopressin concentrations in dementia

In 16 patients with primary degenerative dementia mean CSF vasopressin concentration was lower (0.9 +/- 0.1 pg/ml (mean +/- SEM)) than in 28 control patients (1.3 +/- 0.1 (mean +/- SEM)) (p less than 0.01). In 18 patients with normal pressure hydrocephalus and potentially reversible dementia mean CSF vasopressin concentration (1.2 pg/ml +/- 0.1 (mean +/- SEM)) was not different from that found in controls. Several of the demented patients had inappropriate plasma vasopressin concentrations suggesting a defect in osmoregulation. These findings encourage further clinical trials of vasopressin in patients with primary degenerative dementia, but it is emphasised that the low CSF vasopressin concentration in these patients might be only a nonspecific phenomenon due to the diffuse loss of cells within the central nervous system.