Role of plasma arginine vasopressin in the impaired water diuresis of isolated glucocorticoid deficiency in the rat

Copeptin Levels Before and After Transsphenoidal Surgery for Cushing Disease: A Potential Early Marker of Remission

Context

Arginine-vasopressin (AVP) and corticotropin-releasing hormone (CRH) act synergistically to stimulate secretion of adrenocorticotropic hormone (ACTH). There is evidence that glucocorticoids act via negative feedback to suppress AVP secretion.

Objective

Our hypothesis was that a post-operative increase in plasma copeptin may serve as a marker of remission of Cushing Disease (CD).

Design

Plasma copeptin was obtained in patients with CD before and daily on post-operative days 1-8 after transsphenoidal surgery. Peak post-operative copeptin levels and Δcopeptin values were compared among those in remission versus no remission.

Results

Forty-four patients (64% female, 7-55 years old) were included, and 19 developed neither DI nor SIADH. Thirty-three had follow-up at least 3 months post-operatively. There was no difference in peak post-operative copeptin in remission [6.1 pmol/L (4.3-12.1)] versus no remission [7.3 pmol/L (5.4-8.4), p=0.88].. Excluding those who developed DI or SIADH, there was no difference in peak post-operative copeptin in remission [10.2 pmol/L (6.9-21.0)] versus no remission [5.4 pmol/L (4.6-7.3), p= 0.20]. However, a higher peak post-operative copeptin was found in those in remission [14.6 pmol/L (±10.9) vs. 5.8 (±1.4), p=0.03]] with parametric testing. There was no difference in the Δcopeptin by remission status.

Conclusions

A difference in peak post-operative plasma copeptin as an early marker to predict remission of CD was not consistently present, although the data point to the need for a larger sample size to further evaluate this. However, the utility of this test may be limited to those who develop neither DI nor SIADH post-operatively.

A case of neonatal diabetes insipidus following dexamethasone for bronchopulmonary dysplasia

BACKGROUND

Diabetes insipidus (DI) is a disease resulting from defects in the arginine vasopressin system responsible for regulating body water homeostasis. It is characterized by polyuria with increased serum osmolality and sodium and can result from congenital or acquired disorders.

CLINICAL PRESENTATION

A baby was admitted to NICU for extreme prematurity (25 weeks gestation), extreme low birth weight (900 grams) and respiratory distress. He received one dose of Surfactant and was ventilated using high frequency jet ventilation for development of pulmonary interstitial emphysema. After nine days, he still required high settings with development of early chronic lung changes in the form of atelectasis. Therefore, he was started on a course of dexamethasone following the DART study protocol (Dexamethasone: A Randomized Trial). However, after six days (cumulative dose of 0.75 mg/kg/day) he developed polyuria (7.4 ml/kg/h) with increased serum sodium (150 mmol/L) and osmolality (348 mmol/L). He lost 85 grams of his weight in 24 hours, which represented a 9.8 %weight loss. The findings were suggestive of DI and given there were no apparent causes other than dexamethasone, it was discontinued. Over the following 48 hours, polyuria and hypernatremia gradually resolved, reaching 3.5 ml/kg/h, and 140 mmol/L respectively.

CONCLUSION

The use of dexamethasone is not an uncommon practice in tertiary care neonatal units. To our knowledge, our case is the first report of neonatal DI secondary to the use of dexamethasone. We recommend closely monitoring urine output and serum electrolytes in preterm infants receiving dexamethasone.

Central diabetes insipidus unmasked by corticosteroid therapy for cerebral metastases: beware the case with pituitary involvement and hypopituitarism

Patients with intra-cerebral metastases often receive glucocorticoids, particularly in the presence of peri-lesional vasogenic cerebral oedema. We present a case of presumptive lung carcinoma with cerebral metastases where central diabetes insipidus was unmasked after glucocorticoid administration and correction of undiagnosed central hypocortisolism.

Hyponatremia in Critically Ill Patients

Disorders of sodium and water metabolism are frequently encountered in hospitalized patients. Hyponatremia in critically ill patients can cause significant morbidity and mortality. Inappropriate treatment of hyponatremia can add to the problem. The diagnosis and management of salt and water abnormalities in critically ill patients is often challenging. The increasing knowledge about aquaporins and the role of vasopressin in water metabolism has enhanced our understanding of these disorders. The authors have outlined the general approach to the diagnosis and management of hyponatremia. A systematic approach by clinicians, using a detailed history, physical examination, and relevant diagnostic tests, will assist in efficient management of salt and water problems.

Case seminar: a young female with acute hyponatremia and a sellar mass

In familial cases of combined pituitary hormone deficiency the most common mutations are that of Prophet of Pit 1 (PROP1) gene. PROP1 mutations are associated with deficiencies of growth hormone, thyrotropin, prolactin, and gonadotropins (follicle-stimulating hormone and luteinizing hormone), with evolving adrenocorticotropin (ACTH) deficiency in some cases. On imaging in most patients the pituitary gland is hypoplastic, but occasionally transient pituitary enlargement is found. We report a 22-year-old female initially diagnosed at age 12 with familial hypopituitarism due to PROP1 mutation, who presented with coma and respiratory arrest (acute hyponatremia). She was urgently treated in Intensive Care Unit of Emergency Center with hypertonic saline and stress doses of hydrocortisone, which resulted in the fast increase of plasma osmolality resulting in the osmotic demyelination syndrome. Simultaneously and incidentally on computed tomography scan a large sellar and suprasellar mass were reported as possible Rathke's cleft cyst or craniopharyngioma. Once the patient was stable, ACTH deficiency was documented. She remained replaced with hydrocortisone and subsequently underwent transphenoidal surgery. The removed sellar content revealed no pituitary adenoma or pituitary cells, but only an eosinophilic, colloid-like mass, and necrotic acellular debris. Her sister with hypopituitarism had an empty sella. Genetic testing in both sisters revealed the same homozygous c.150delA mutation in PROP1 gene. Here we report two sisters with the same PROP1 mutation who presented in adulthood with different pituitary morphology, one of them with a large sellar and suprasellar mass, in which transphenoidal surgery provided an extremely rare opportunity for a histopathological analysis of the sellar content. Due to the lack of endocrine care during the transition period hypocortisolism which evolved, a consequence of PROP1 mutation, was not recognized. Empirical use of hydrocortisone in the Intensive Care in our patient with life-threatening acute hyponatremia was appropriate but because glucocorticoid therapy on its own corrects hyponatremia even after stopping hypertonic saline infusion, the risk for over-correction of hyponatremia in ACTH deficiency is high.

Hyponatremia in the intensive care unit

Hyponatremia is a common electrolyte disturbance encountered in the intensive care unit setting. The underlying etiology is multifactorial and includes processes that lead to both a baroreceptor-mediated and a baroreceptor independent increase in antidiuretic hormone release. Patients with hyponatremia have an increased mortality rate and therefore an understanding of the cause and treatment of this disorder is of paramount importance.

Treatment of hyponatremia

Hyponatremia is an electrolyte disorder that is defined by a serum sodium concentration of less than 136 mmol/L. Hyponatremia occurs at a high incidence. It is commonly associated with mild to moderate mental impairment. Hypoosmolar hyponatremia occurs in the setting of plasma volume deficiency ("hypovolemia", e. g. after gastrointestinal fluid loss), liver cirrhosis and cardiac failure ("hypervolemic" hyponatremia) and syndrome of inappropriate antidiuretic hormone secretion ("euvolemic" hyponatremia). Excessive antidiuretic hormone and continued fluid intake are the pathogenetic causes of these hyponatremias. Whereas hypovolemic hyponatremia is best corrected by isotonic saline, conventional proposals for euvolemic and hypervolemic hyponatremia consist of the following: fluid restriction, lithium carbonate, demeclocycline, urea and loop diuretic. None of these nonspecific treatments is entirely satisfactory. Recently a new class of pharmacological agents -orally available vasopressin antagonists, collectively called vaptans- have been described. A number of clinical trials using vaptans have been performed already. They showed vaptans to be effective, specific and safe in the treatment of euvolemic and hypervolemic hyponatremia.

Vaptans and the treatment of water-retaining disorders

Hyponatremia is a frequent and symptomatic electrolyte disorder for which specific treatments have been lacking. Hyponatremia is attributable to nonosmotic vasopressin stimulation and continued increased fluid intake. In the past, peptidic derivatives of arginine vasopressin proved that blockade of vasopressin V-2 receptors served to improve hyponatremia, however, these antagonists had intrinsic agonistic activity, too. In the past decade, random screening of molecules uncovered nonpeptide, orally available vasopressin antagonists without agonistic properties. The agents show competitive binding to the vasopressin V-2 receptor at an affinity comparable with that of arginine vasopressin. Four antagonists have undergone extensive study. Three of these agents--lixivaptan or VPA 985; SR 121 463 B; tolvaptan or OPC 41,061--are specific V-2 antagonists whereas conivaptan or YM 087 is a V-1/V-2 mixed antagonist. In animal and clinical studies all of the agents were able to correct water retention and hyponatremia in a dose-dependent manner. There was no tachyphylaxis, even when the agents were given over many weeks. It is expected that the clinical use of the agents will lead to a major improvement in the treatment of hyponatremia.

Regulation of collecting duct AQP3 expression: response to mineralocorticoid

Adrenocortical steroid hormones are importantly involved in the regulation of extracellular fluid volume. The present study was aimed at examining whether aldosterone and/or glucocorticoid regulates the abundance of aquaporin-3 (AQP3), -2, and -1 in rat kidney. In protocol 1, rats were adrenalectomized, followed by aldosterone replacement, dexamethasone replacement, or combined aldosterone and dexamethasone replacement (rats had free access to water but received a fixed amount of food). Protocol 2 was identical to protocol 1, except that all groups received fixed daily food and water intake. In both protocols 1 and 2, aldosterone deficiency was associated with increased fractional Na excretion and severe hyperkalemia. Semiquantitative immunoblotting revealed that aldosterone deficiency was associated with a dramatic downregulation of AQP3 abundance. Consistent with this, immunocytochemistry and immunoelectron microscopy revealed a marked decrease in AQP3 labeling in the basolateral plasma membranes of collecting duct principal cells. In contrast, AQP1 and AQP2 abundance and distribution were unchanged. Glucocorticoid deficiency revealed no changes in AQP3, -2, or -1 abundance. In protocol 3, Na restriction (to increase endogenous aldosterone levels) or exogenous aldosterone infusion in either normal rats or vasopressin-deficient Brattleboro rats was associated with a major increase in AQP3 abundance. In protocol 4, aldosterone levels were clamped by infusion of aldosterone, while Na intake was altered from a low to a high level. Under these circumstances, there were no changes in AQP3 or AQP2 abundance, although the level of the thiazide-sensitive Na-Cl cotransporter was decreased. In conclusion, the results uniformly demonstrate that aldosterone regulates AQP3 abundance independently of Na intake. In contrast, changes in glucocorticoid levels in these models do not influence AQP3 or AQP2 abundance. Therefore, in the collecting duct aldosterone may regulate, at least in part, AQP3 expression in addition to regulating Na and K transport.

Impairment of AVP regulation in 17alpha-hydroxylase deficiency, a unique form of adrenal insufficiency

17alpha-hydroxylase deficiency (17alpha-OHDS) results in decreased production of cortisol and sex steroids and hypokalemia secondary to excess mineralocorticoids. It has long been known that glucocorticoid deficiency is associated with impaired urinary dilution and increased secretion of vasopressin (AVP). On the other hand, chronic hypokalemia is a well-established cause of nephrogenic diabetes insipidus. We evaluated the status of AVP secretion in a patient with 17alpha-OHDS and in 8 normokalaemic control subjects during hypertonic saline infusion (5% NaCl 0.06 ml.kg.min.120 min). The patient was evaluated on 3 separate occasions: pre-treatment (PT), and daily treatment with 0.375 mg (T1) and 0.5 mg (T2) dexamethasone. Blood was collected for AVP, corticosterone (B), plasma osmolality (pOsm) and electrolyte determination. In the control group plasma AVP levels increased from 0.8 +/- 0.1 to 4.1 +/- 0.6 pmol/l and pOsm increased from 282 +/- 2 to 302 +/- 11.5 mosmol/kg. In the patient, plasma AVP levels increased from 9.3 to 12.3; 4.5 to 6.2; and 2.5 to 6.2 pmol/l, and pOsm increased from 282 to 302, from 290 to 307, and from 291 to 311 mosmol/kg during the PT, T1 and T2 conditions, respectively. Serum potassium levels were low (2.6 mmol/l) during PT and reached normal values after treatment. There was a significant negative correlation between plasma AVP and serum potassium levels (r=-0.71; p<0.001). The results originally indicate that high plasma AVP levels may be found in 17alpha-OHDS, suggesting an effect of F deficiency per se. In addition, a concealed partial nephrogenic diabetes insipidus secondary to chronic hypokalemia cannot be excluded.

Role of glucocorticoid hormones in arginine vasopressin gene regulation

The mechanism underlying increased AVP synthesis and release in glucocorticoid deficiency is not known. Therefore, the present study was undertaken to investigate whether the mechanism was at the level of AVP gene transcription. The AVP gene promoter contains a consensus GRE, a CRE, and four AP2 sites. To assess the functional importance of these sites, 5' deletions of the AVP promoter were created and transient transfections were performed. Promoter activity in hypothalamic cells transfected with deletions lacking the GRE or both the GRE and CRE exhibited higher activity when compared to longer constructs containing both sites. In neuroblastoma cells, only the deletion lacking the GRE exhibited increased AVP promoter activity over the longer construct. These results are consistent with the idea that glucocorticoids suppress AVP gene expression by acting on a GRE in the AVP promoter region. Further, dexamethasone inhibited AVP promoter activity by >50% in hypothalamic cells transfected with the GRE-containing construct. In conclusion, the data presented here support a central mechanism to explain, at least in part, the nonosmotic increase in AVP with glucocorticoid deficiency.

Hyponatremia and hypernatremia

Hyponatremia and hypernatremia are common electrolyte disorders resulting from disorders in water homeostasis. Hyponatremia usually results from defects in free water excretion, although increased intake may also contribute. The treatment of hyponatremia has been controversial because of the high associated morbidity and mortality and the observation that rapid correction of hyponatremia is associated with the development of central pontine myelinolysis. Mild hyponatremia should be treated with water restriction alone, whereas severe acute or symptomatic hyponatremia should initially be corrected rapidly until symptoms resolve followed by more gradual correction. In all cases, treatment should be individualized on the basis of severity, cause, and duration of the hyponatremia. Hypernatremia results from impaired water ingestion, although increased water losses are often contributory. Hospital-acquired hypernatremia is usually iatrogenic because of inadequate water prescription and is therefore preventable. Hypernatremia is also associated with high morbidity and mortality, both as a result of the underlying disease and inadequate treatment. The primary treatment of hypernatremia is water replacement-repleting water deficits and replacing ongoing losses. Additional treatment should be directed at eliminating excess water losses.

A case of Sheehan's syndrome with delirium

A 53 year old woman was brought to a psychiatric clinic because of delirium. Upon immediate examination, severe hyponatremia (105 mEq/L) was detected. She was suspected of having internal diseases and referred to our university hospital. When she reached our hospital she was delirious and showed excitement and agitation. Her electroencephalogram showed low voltage theta waves (20 microV) in all leads. She was hospitalized and diagnosed with acute tonsillar abscess and panhypopituitarism based on various endocrine tests. Her past history suggested that Sheehan's syndrome had developed after child-bearing at age 31, resulting in panhypopituitarism. After administration of antibiotics, the fever and tonsillar abscess gradually recovered, and the correction of electrolytes improved the level of consciousness, suggesting that the hyponatremia had been closely related to the clouding of consciousness. As the subsequent administration of cortisol kept the patient's serum sodium levels within the normal range, a decrease in plasma cortisol seemed to be the major cause of the hyponatremia. Psychological symptoms of panhypopituitarism often included abulia, apathy and occasionally coma. However, it is rare for a patient with panhypopituitarism to be misdiagnosed as having a psychiatric disease with delirium. This rare case is presented.

Hyponatraemia in AIDS

Hyponatraemia is very common in AIDS patients. It is observed in about 40-50% of hospitalized patients. It may contribute to overall mortality in advanced disease. Vasopressin measurements in these patients basically present two distinct syndromes: hyponatraemia and 'normal' vasopressin levels (i.e. measurable vasopressin) and hyponatraemia with suppressed vasopressin. Hyponatraemia with suppressed vasopressin is very rare and has only been observed in AIDS patients with dementia and primary polydipsia. Hyponatraemia and measurable vasopressin can be also divided into two syndromes. In some patients vasopressin is 'appropriately' elevated, i.e. in those with body fluid losses (diarrhoea) or chronic hypovolaemia (adrenal failure); these patients also present with hyperuricaemia and other signs of low blood volume. In other patients vasopressin is 'inappropriately' elevated in those with no clinical evidence of hypovolaemia (typically characterized by low serum uric acid levels) such as in Pneumocystis carinii pneumonia and other opportunistic infections leading to SIADH. CSWS is a relatively frequent complication in some patients with cerebral infection or tumour. High-dose trimethoprim (for Pneumocystis carinii prevention) acts as an amiloride-like drug and induces a clinical state characterized by hyponatraemia and hyperkalaemia which is indistinguishable from hyporeninaemic hypoaldosteronism. The mechanism of the hyponatraemia caused by other drugs (miconazole, pentamidine, amphotericin, vidarabine) is not as yet known.

Inappropriate secretion of antidiuretic hormone in isolated adrenocorticotropin deficiency

A 62-year-old man was admitted because of nausea and vomiting. Severe hyponatremia with renal sodium loss was found. Endocrinological studies revealed that the patient had isolated adrenocorticotropin (ACTH) deficiency and secondary adrenocortical insufficiency. Furthermore, an inappropriate secretion of antidiuretic hormone (ADH) in relation to the low plasma osmolality was observed at an early stage of hyponatremia. Hydrocortisone therapy effectively corrected his hyponatremia. Following the correction of hyponatremia, the value of free water clearance increased and the level of the plasma ADH decreased. Thus, the present case indicates that ACTH deficiency can cause the syndrome of inappropriate secretion of ADH.

Hyponatremia and inappropriate secretion of vasopressin (antidiuretic hormone) in patients with hypopituitarism

Severe hyponatremia occurs in some patients with untreated hypopituitarism, but it is not known whether such hyponatremia is caused by the hypersecretion of vasopressin (antidiuretic hormone). This report describes severe, symptomatic hyponatremia in five women 59 to 83 years old (serum sodium, 111 to 118 mmol per liter) who presented with hypopituitarism (which had been previously undiagnosed in four). Plasma vasopressin was inappropriately high (1.3 to 25.8 pmol per liter [1.4 to 28 ng per liter]) in relation to plasma osmolality (236 to 260 mOsm per kilogram of body weight). All five patients had normal renal function and no signs of dehydration or volume depletion. The hyponatremia was resolved within a few days after the institution of hydrocortisone therapy, after infusion of normotonic or hypertonic saline had been found to be less effective. When four of the patients were later restudied while receiving maintenance hydrocortisone treatment, the relation between plasma vasopressin and osmolality was normal. We conclude that ACTH deficiency may cause the syndrome of inappropriate secretion of antidiuretic hormone. The beneficial effect of hydrocortisone is probably exerted through the suppression of vasopressin secretion.

Dissociation between activation of the hypothalamo-hypophyseal antidiuretic system and the type of diuresis during acute intracranial hypertension. Experimental observation

Acute cerebral compression by a supra- and infratentorial balloon produced a triphasic pattern of diuresis. The 1st phase was characterized by polyuria associated with five fold increase of plasma (p) antidiuretic hormone (ADH) concentration, decreased urine osmolality in spite of natriuresis and blood pressure elevation. The 2nd phase was characterized by oliguria, a decrease of pADH and reduced urine Na+ concentration, whereas urine osmolality transiently increased. At this stage there was respiratory arrest and fall of blood pressure. The final stage was diabetes insipidus (DI), when EEG activity had disappeared. An increase of serum osmolality mainly occurred during the last DI phase. Serum Na+ concentration fluctuated slightly during the whole period of diuresis. These results present evidence, that the diuresis pattern reflects the hypothalamo-hypophyseal antidiuretic system (HHAS) reaction to acute intracranial pressure (ICP) increase with the vegetative symptoms of cerebral shock.

Effect of frusemide on urinary kallikrein excretion in the conscious rat: influence of adrenalectomy and DOCA treatment

The effect of subcutaneous frusemide administration on urinary kallikrein excretion was studied in the conscious state, in control, adrenalectomized and DOCA-treated adrenalectomized rats. Frusemide increased urinary kallikrein excretion in the three groups of rats. Urine volume and urinary sodium and potassium excretions were also increased. These responses were however suppressed by adrenalectomy but normalized by DOCA treatment. It is concluded that frusemide's stimulation of urinary kallikrein excretion in the conscious rat is modulated by mineralocorticoid activity.

Beneficial effect of thyroxin on recovery from toxic acute renal failure

To determine the effect of thyroxin (T4) on the recovery from toxic acute renal failure, rats were injected, subcutaneously, with K-dichromate (15 mg/kg) and at the peak of the renal injury, each animal was given either T4 (4 micrograms/100 g body weight, i.p.) or normal saline (NS). The T4-treated rats had significantly better CIn (669 +/- 35 microliter/min/100 g body weight), improved FENa (0.49 +/- 0.05%) and increased UOsm (835 +/- 50 mOsm/kg) as compared to animals given only NS (CIn 422 +/- 27; FENa 1.02 +/- 0.12; and UOsm 613 +/- 23). A similar dose of T4 given to non-injured control rats had no effect on renal function. The beneficial effect of T4 on dichromate injected rats was sustained and lead to more prompt recovery of glomerular function. To eliminate any hemodynamic effects of T4, an isolated perfused kidney preparation was utilized, and kidneys from dichromate injected rats treated with T4 had significantly better CIn, urine flow and FENa compared to rats given NS. Cellular morphology was better preserved in T4-treated animals. These data indicate that treatment with T4 results in enhanced recovery from an acute toxic renal insult and that this beneficial effect is unlikely to be related to nonspecific systemic effects of the hormone.

Addison's disease, psychosis, and the syndrome of inappropriate secretion of antidiuretic hormone

A case of tuberculous Addison's disease presenting with psychosis, profound hyponatraemia, and detectable plasma antidiuretic hormone is reported. Clinical and biochemical improvement after corticosteroid replacement was followed by relapse with further psychosis and inappropriate antidiuretic hormone secretion: both were promptly reversed by demethylchlortetracycline. The association of psychological symptoms with Addison's disease, the role of anti-diuretic hormone secretion in Addison's disease, and the inter-relationship between Addison's disease, psychosis and anti-diuretic hormone secretion are discussed.

Mechanism of increased renin release in the adrenalectomized rat. Adrenal insufficiency and renin

We have previously suggested that inhibition of renin release by sodium chloride is related to absorptive chloride transport in the loop of Henle. Infusion of sodium chloride fails to inhibit renin release in the adrenalectomized (Adx) rat, and dexamethasone restores renin responsiveness to sodium chloride. The purpose of the present study was to evaluate the relationship between loop function (urinary diluting and concentration capacity) and plasma renin concentration (PRC) in the Adx rat. After hypotonic sodium chloride infusion, free water clearance (CH2O) of Adx rats (0.56 ml/hr/100 g +/- 0.17 SE) was decreased (p less than 0.01) compared to controls (2.86 ml/hr/100 g +/- 0.29 SE); PRC of Adx rats (61.9 units/ml +/- 11.2 SE) was increased (p less than 0.01) above controls (6.0 units/ml +/- 1.7 SE). These differences persisted after administration of d(CH2)5Tyr(Et)VAVP, a potent ADH antagonist. In separate groups of animals, after water deprivation, urine concentration of Adx rat (1,401 mOsm/kg +/- 45 SE) was less (p less than 0.01) than that of controls (2,117 mOsm/kg +/- 169 SE). Dexamethasone normalized both CH2O and urinary concentrating ability and also decreased PRC in Adx rats. Thus, in the glucocorticoid deficient rat, increased renin release is associated with impaired loop function. The loop defect may account for high PRC that is not suppressed by sodium chloride.

Neurogenic disorders of osmoregulation

The osmolality of body fluids is normally maintained within a narrow range. This constancy is achieved largely via hypothalamic osmo-receptors that regulate thirst and arginine vasopressin, the antidiuretic hormone (ADH). Anything that interferes with the full expression of either osmoregulatory function exposes the patient to the hazards of abnormal increases or decreases in plasma osmolality. Hyposmolality is almost always due to a defect in water excretion. Increased intake may contribute to the problem but is rarely, if ever, a sufficient cause. Impaired water excretion can be due to a primary defect in the osmoregulation of ADH (inappropriate antidiuresis) or secondary to nonosmotic stimuli like hypovolemia or nausea. The two types differ in clinical presentation and treatment. Resetting of the ADH osmostat is commonly associated with resetting of the thirst osmostat. Hyperosmolarity is almost always due to deficient water intake. Excessive excretion may contribute to the problem but is never a sufficient cause. Impaired water intake can result from a defect in either the osmoregulation of thirst of the necessary motor responses. Thirst may be deficient because of primary osmoreceptor damage as in the syndrome of adipsic hypernatremia or secondary to nonosmotic influences on the set of the system. They are distinguishable by the clinical presentation as well as the type of ADH defects with which they are associated. So-called essential hypernatremia due to primary resetting of the osmostat has been postulated, but unambiguous evidence for such an entity has not yet been reported.