Clofibrate-induced antidiuresis

Diagnosis and Management of Central Diabetes Insipidus in Adults

Central diabetes insipidus (CDI) is a clinical syndrome which results from loss or impaired function of vasopressinergic neurons in the hypothalamus/posterior pituitary, resulting in impaired synthesis and/or secretion of arginine vasopressin (AVP). AVP deficiency leads to the inability to concentrate urine and excessive renal water losses, resulting in a clinical syndrome of hypotonic polyuria with compensatory thirst. CDI is caused by diverse etiologies, although it typically develops due to neoplastic, traumatic, or autoimmune destruction of AVP-synthesizing/secreting neurons. This review focuses on the diagnosis and management of CDI, providing insights into the physiological disturbances underpinning the syndrome. Recent developments in diagnostic techniques, particularly the development of the copeptin assay, have improved accuracy and acceptability of the diagnostic approach to the hypotonic polyuria syndrome. We discuss the management of CDI with particular emphasis on management of fluid intake and pharmacological replacement of AVP. Specific clinical syndromes such as adipsic diabetes insipidus and diabetes insipidus in pregnancy as well as management of the perioperative patient with diabetes insipidus are also discussed.

Central Diabetes Insipidus Masked by Uncontrolled Diabetes Mellitus: A Challenging Case Managed With Indapamide

A 44-year-old man with a history of traumatic brain injury (TBI) presented to the emergency room (ER) with diabetic ketoacidosis (DKA). After resolution of DKA, the patient had persistent polyuria (up to 5.5 L/24 h) associated with low specific gravity (1.002-1.005) and severe hypernatremia (up to 186 mmol/L) that led us to consider the possibility of central diabetes insipidus (DI). Due to the lack of desmopressin availability in our country, we managed the patient using indapamide. Polydipsia and polyuria in a patient with controlled diabetes mellitus (DM) should raise suspicion for alternative etiologies, including DI. Appropriate fluid management during hospitalization is critical to avoid life-threatening complications. TBI is an important cause of central DI and should be treated with desmopressin, an arginine-vasopressin (AVP) analog. In the absence of desmopressin, alternative options can help patients with central DI, including thiazides, carbamazepine, chlorpropamide, among others less studied.

Management of central diabetes insipidus

The treatment of central diabetes insipidus has not changed significantly in recent decades, and dDAVP and replacement of free water deficit remain the cornerstones of treatment. Oral dDAVP has replaced nasal dDAVP as a more reliable mode of treatment for chronic central diabetes insipidus. Hyponatraemia is a common side effect, occurring in one in four patients, and should be avoided by allowing a regular break from dDAVP to allow a resultant aquaresis. Hypernatraemia is less common, and typically occurs during hospitalization, when access to water is restricted, and in cases of adipsic DI. Management of adipsic DI can be challenging, and requires initial inpatient assessment to establish dose of dDAVP, daily fluid prescription, and eunatraemic weight which can guide day-to-day fluid targets in the long-term.

Nephrogenic Diabetes Insipidus

Body fluid homeostasis is essential for normal life. In the maintenance of water balance, the most important factor and regulated process is the excretory function of the kidneys. The kidneys are capable to compensate not only the daily fluctuations of water intake but also the consequences of fluid loss (respiration, perspiration, sweating, hemorrhage). The final volume and osmolality of the excreted urine is set in the collecting duct via hormonal regulation. The hormone of water conservation is the vasopressin (AVP), and a large volume of urine is produced and excreted in the absence of AVP secretion or if AVP is ineffective in the kidneys. The aquaporin-2 water channel (AQP2) is expressed in the principal cells, and it plays an essential role in the reabsorption of water in the collecting ducts via type 2 vasopressin receptor (V2R)-mediated mechanism. If neural or hormonal regulation fails to operate the normal function of AVP-V2R-AQP2 system, it can result in various diseases such as diabetes insipidus (DI) or nephrogenic syndrome of inappropriate diuresis (NSIAD). The DI is characterized by excessive production of hyposmotic urine ("insipidus" means tasteless) due to the inability of the kidneys to concentrate urine. In this chapter, we focus and discuss the pathophysiology of nephrogenic DI (NDI) and the potential therapeutic interventions in the light of the current experimental data.

Adipsic diabetes insipidus in adult patients

INTRODUCTION

Adipsic diabetes insipidus (ADI) is a very rare disorder, characterized by hypotonic polyuria due to arginine vasopressin (AVP) deficiency and failure to generate the sensation of thirst in response to hypernatraemia. As the sensation of thirst is the key homeostatic mechanism that prevents hypernatraemic dehydration in patients with untreated diabetes insipidus (DI), adipsia leads to failure to respond to aquaresis with appropriate fluid intake. This predisposes to the development of significant hypernatraemia, which is the typical biochemical manifestation of adipsic DI.

METHODS

A literature search was performed to review the background, etiology, management and associated complications of this rare condition.

RESULTS

ADI has been reported to occur in association with clipping of an anterior communicating artery aneurysm following subarachnoid haemorrhage, major hypothalamic surgery, traumatic brain injury and toluene exposure among other conditions. Management is very difficult and patients are prone to marked changes in plasma sodium concentration, in particular to the development of severe hypernatraemia. Associated hypothalamic disorders, such as severe obesity, sleep apnoea and thermoregulatory disorders are often observed in patients with ADI.

CONCLUSION

The management of ADI is challenging and is associated with significant morbidity and mortality. Prognosis is variable; hypothalamic complications lead to early death in some patients, but recent reports highlight the possibility of recovery of thirst.

Use of Chlorothiazide in the Management of Central Diabetes Insipidus in Early Infancy

Management of central diabetes insipidus in infancy is challenging. The various forms of desmopressin, oral, subcutaneous, and intranasal, have variability in the duration of action. Infants consume most of their calories as liquids which with desmopressin puts them at risk for hyponatremia and seizures. There are few cases reporting chlorothiazide as a temporizing measure for central diabetes insipidus in infancy. A male infant presented on day of life 30 with holoprosencephaly, cleft lip and palate, and poor weight gain to endocrine clinic. Biochemical tests and urine output were consistent with central diabetes insipidus. The patient required approximately 2.5 times the normal fluid intake to keep up with the urine output. Patient was started on low renal solute load formula and oral chlorothiazide. There were normalization of serum sodium, decrease in fluid intake close to 1.3 times the normal, and improved urine output. There were no episodes of hyponatremia/hypernatremia inpatient. The patient had 2 episodes of hypernatremia in the first year of life resolving with few hours of hydration. Oral chlorothiazide is a potential bridging agent for treatment of central DI along with low renal solute load formula in early infancy. It can help achieve adequate control of DI without wide serum sodium fluctuations.

Diabetes insipidus: The other diabetes

Diabetes insipidus (DI) is a hereditary or acquired condition which disrupts normal life of persons with the condition; disruption is due to increased thirst and passing of large volumes of urine, even at night. A systematic search of literature for DI was carried out using the PubMed database for the purpose of this review. Central DI due to impaired secretion of arginine vasopressin (AVP) could result from traumatic brain injury, surgery, or tumors whereas nephrogenic DI due to failure of the kidney to respond to AVP is usually inherited. The earliest treatment was posterior pituitary extracts containing vasopressin and oxytocin. The synthetic analog of vasopressin, desmopressin has several benefits over vasopressin. Desmopressin was initially available as intranasal preparation, but now the oral tablet and melt formulations have gained significance, with benefits such as ease of administration and stability at room temperature. Other molecules used for treatment include chlorpropamide, carbamazepine, thiazide diuretics, indapamide, clofibrate, indomethacin, and amiloride. However, desmopressin remains the most widely used drug for the treatment of DI. This review covers the physiology of water balance, causes of DI and various treatment modalities available, with a special focus on desmopressin.

The renal concentrating mechanism and the clinical consequences of its loss

The integrity of the renal concentrating mechanism is maintained by the anatomical and functional arrangements of the renal transport mechanisms for solute (sodium, potassium, urea, etc) and water and by the function of the regulatory hormone for renal concentration, vasopressin. The discovery of aquaporins (water channels) in the cell membranes of the renal tubular epithelial cells has elucidated the mechanisms of renal actions of vasopressin. Loss of the concentrating mechanism results in uncontrolled polyuria with low urine osmolality and, if the patient is unable to consume (appropriately) large volumes of water, hypernatremia with dire neurological consequences. Loss of concentrating mechanism can be the consequence of defective secretion of vasopressin from the posterior pituitary gland (congenital or acquired central diabetes insipidus) or poor response of the target organ to vasopressin (congenital or nephrogenic diabetes insipidus). The differentiation between the three major states producing polyuria with low urine osmolality (central diabetes insipidus, nephrogenic diabetes insipidus and primary polydipsia) is done by a standardized water deprivation test. Proper diagnosis is essential for the management, which differs between these three conditions.

Syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in malignant disease

The first clinical case of a patient with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) was presented by Schwartz et al. in 1957 (Am J Med 1957; 23: 529-42), describing two patients with lung cancer who developed hyponatraemia associated with continued urinary sodium loss. They postulated that the tumours led to the inappropriate release of antidiuretic hormone (ADH), later discovered to consist of arginine-vasopressin (AVP). This suggestion was later confirmed in several studies. The clinical description of the syndrome has changed little since the original observation, and the cardinal findings of SIADH are as follows: (i) hyponatraemia with corresponding hypo-osmolality of the serum and extracellular fluid, (ii) continued renal excretion of sodium. (iii) absence of clinical evidence of fluid volume depletion, (iv) osmolality of the urine greater than that appropriate for the concomitant osmolality of the plasma, i.e. urine less than maximal diluted, and (v) normal function of kidneys, suprarenal glands and thyroid glands. Measurement of AVP in plasma is not a part of the definition of SIADH. SIADH may be caused by a variety of malignant tumours, but may also be caused by various other conditions, such as disorders involving the central nervous system, intrathoratic disorders such as infections, positive pressure ventilation and conditions with decrease in left atrial pressure. Also, a large number of pharmaceutical agents have been shown to produce SIADH, including a number of cytotoxic drugs such as vincristine, vinblastine, cisplatin, cyclophosphamide, and melphalan. A broad spectrum of malignant tumours has been reported to cause SIADH; however, most of these observations have been in case reports including very few patients. This includes a number of primary brain tumours, haematologic malignancies, intrathoracic non-pulmonary cancers, skin tumours, gastrointestinal cancers, gynaecological cancer, breast-and prostatic cancer, and sarcomas. Larger series of patients have revealed that SIADH occurs in 3% of patients with head and neck cancer (47 cases out of 1696 patients), in 0.7% of patients with non-small-cell lung cancer (three cases out of 427 patients), and in 15% of cases of small-cell lung cancer (214 cases out of 1473 patients). The optimal therapy for SIADH is to treat the underlying malignant disease. If this is not possible, or if the disease has become refractory, other treatment methods are available such as water restriction, demeclocycline therapy, or, in severe cases, infusion of hypertonic saline together with furosemide during careful monitoring.

Deletion of the vaccinia virus B5R gene encoding a 42-kilodalton membrane glycoprotein inhibits extracellular virus envelope formation and dissemination

The structure, formation, and function of the virion membranes are among the least well understood aspects of vaccinia virus replication. In this study, we investigated the role of gp42, a glycoprotein component of the extracellular enveloped form of vaccinia virus (EEV) encoded by the B5R gene. The B5R gene was deleted by homologous recombination from vaccinia virus strains IHD-J and WR, which produce high and low levels of EEV, respectively. Isolation of recombinant viruses was facilitated by the insertion into the genome of a cassette containing the Escherichia coli gpt and lacZ genes flanked by the ends of the B5R gene to provide simultaneous antibiotic selection and color screening. Deletion mutant viruses of both strains formed tiny plaques, and those of the IHD-J mutant lacked the characteristic comet shape caused by release of EEV. Nevertheless, similar yields of intracellular infectious virus were obtained whether cells were infected with the B5R deletion mutants or their parental strains. In the case of IHD-J, however, this deletion severely reduced the amount of infectious extracellular virus. Metabolic labeling studies demonstrated that the low extracellular infectivity corresponded with a decrease in EEV particles in the medium. Electron microscopic examination revealed that mature intracellular naked virions (INV) were present in cells infected with mutant virus, but neither membrane-wrapped INV nor significant amounts of plasma membrane-associated virus were observed. Syncytium formation, which occurs in cells infected with wild-type WR and IHD-J virus after brief low-pH treatment, did not occur in cells infected with the B5R deletion mutants. By contrast, syncytium formation induced by antibody to the viral hemagglutinin occurred, suggesting that different mechanisms are involved. When assayed by intracranial injection into weanling mice, both IHD-J and WR mutant viruses were found to be significantly attenuated. These findings demonstrate that the 42-kDa glycoprotein of the EEV is required for efficient membrane enwrapment of INV, externalization of the virus, and transmission and that gp42 contributes to viral virulence in strains producing both low and high levels of EEV.

Statistical analysis of sparse infection data and its implications for retroviral treatment trials in primates

Reports on retroviral primate trials rarely publish any statistical analysis. Present statistical methodology lacks appropriate tests for these trials and effectively discourages quantitative assessment. This paper describes the theory behind VACMAN, a user-friendly computer program that calculates statistics for in vitro and in vivo infectivity data. VACMAN's analysis applies to many retroviral trials using i.v. challenges and is valid whenever the viral dose-response curve has a particular shape. Statistics from actual i.v. retroviral trials illustrate some unappreciated principles of effective animal use: dilutions other than 1:10 can improve titration accuracy; infecting titration animals at the lowest doses possible can lower challenge doses; and finally, challenging test animals in small trials with more virus than controls safeguards against false successes, "reuses" animals, and strengthens experimental conclusions. The theory presented also explains the important concept of viral saturation, a phenomenon that may cause in vitro and in vivo titrations to agree for some retroviral strains and disagree for others.

Diabetes insipidus and pregnancy

A case of a pregnant woman with diabetes insipidus is reported. The course of the pregnancy was uneventful except for a slightly increased need for vasopressin during the last trimester. Neurophysin levels increased at a rate similar to that seen in the normal pregnant state. The combination of normal neurophysin physiology and undisturbed spontaneous labor demonstrating normal oxytocin secretion suggests that there is a singular deficiency of antidiuretic hormone in essential diabetes insipidus.

Drug prescribing in renal failure: dosing guidelines for adults

The data base for rational guidelines to safe, efficacious drug prescribing in adults with renal insufficiency are presented in tabular form. Current medical literature was extensively surveyed to provide as much specific information as possible. When information is lacking, however, recommendations are based on pharmacokinetic variables in normal subjects. Nephrotoxicity, important adverse effects, and special considerations in renal patients are noted. Adjustments are suggested for hemodialysis and peritoneal dialysis when appropriate.

Drug-induced electrolyte disorders

A wide variety of pharmacologic agents have been implicated in a number of electrolyte disorders. The present review focuses on abnormalities of sodium, potassium, calcium, magnesium, and phosphate. Several mechanisms are involved in the pathogenesis of these disorders. These involve stimulation and modulation of other hormones (e.g., antidiuretic hormone, renin-angiotensin system, parathyroid hormone), damage to renal tubules, and, in some cases, a combination of factors. Recognition of these abnormalities is important because their presence may be life threatening or may aggravate the side effects of the drug itself.

Drug-induced electrolyte abnormalities

Drugs can interfere with the normal intake, elimination, regulation and total body distribution of electrolytes. These drug-induced abnormalities may be dramatic and life threatening, posing diagnostic and management problems to the physician who is not familiar with them. Serum potassium concentrations can be altered as potassium shifts between the tissue and plasma compartments secondary to drug actions. In addition, drugs have been shown to interfere with the normal physiological functioning of the kidney with respect to potassium homeostasis, as well as the renin-aldosterone axis. The regulation of serum sodium levels is integrally related to the regulation of total body water. Thus, drugs that alter the regulation of antidiuretic hormone secretion and its action on the kidney can result in large changes in serum sodium concentrations. Abnormal losses or intake of sodium related to drug use can also have profound effects in the plasma compartment. The normally fine regulation of serum calcium concentrations can be easily upset by pharmacological therapy at the level of parathyroid hormone secretion and action, bone metabolism or renal calcium excretion. Through awareness of these drug-induced changes in electrolytes and the mechanisms involved, subtle and often dangerous problems in clinical management can be handled rationally.

Treatment of diabetes insipidus complicated by diabetes mellitus with chlorpropamide and clofibrate

A patient with severe idiopathic diabetes insipidus, complicated by diabetes mellitus, was first treated with a combination o clofibrate and chlorpropamide. Urine volume dropped from 18 litres/day (CH2O = 10.5 ml/min) to 3.1-5.1 litres/day (CH2O = -0.1 -+1.1 ml/min) under treatment. Ten months after the beginning of therapy treatment was maintained with chlorpropamide alone; no significant rise in urine volume was observed. After 18 months when therapy was stopped for 5 days urine volume rose to 11.7 litres/day maximum (CH2O = 6.6 ml/min). No obvious side effects occurred under treatment during a follow up for over 18 months. Serum levels for arginine vasopressin before and under treatment were below 1.0 pg/ml. Determination of free water clearance (CH2O) proved to be a highly sensitive and simple method for follow up controls. It is discussed whether the coincidental manifestation of diabetes insipidus and diabetes mellitus may be caused by a single molecular lesion. This hypothesis is supported by data which imply that in both disease chlorpropamide acts via a common molecular mechanism, the blocking of endogenous prostaglandin E2 biosynthesis. Finally a treatment with oral "non-hormonal" drugs like clofibrate and chlorpropamide should be taken into consideration in some cases of diabetes insipidus as is demonstrated by this case report.

The clinical physiology of water metabolism. Part II: Renal mechanisms for urinary concentration; diabetes insipidus

The renal reabsorption of water independent of solute is the result of the coordinated function of the collecting duct and the ascending limb of the loop of Henle. The unique juxtaposition of the ascending and descending portions of the loop of Henle and of the vasa recta permits the function of a counter-current multiplier system in which water is removed from the tubular lumen and reabsorbed into the circulation. The driving force for reabsorption is the osmotic gradient in the renal medulla which is dependent, in part, on chloride (followed by sodium) pumping from the thick ascending loop of Henle. Urea trapping is also thought to play an important role in the generation of a hypertonic medullary interstitium. Arginine vasopressin (AVP) acts by binding to receptors on the cell membrane and activating adenylate cyclase. This, inturn, results in the intracellular accumulation of cyclic adenosine monophosphate (AMP) which in some fashion abruptly increases the water permeability of the luminal membrane of cells in the collecting duct. As a consequence, water flows along an osmotic gradient out of the tubular lumen into the medullary interstitium. Diabetes insipidus is the clinical condition associated with either a deficiency of or a resistance to AVP. Central diabetes insipidus is due to diminished release of AVP following damage to either the neurosecretory nuclei or the pituitary stalk. Possible causes include idiopathic, familial, trauma, tumor, infection or vascular lesions. Patients present with polyuria, usually beginning over a period of a few days. The diagnosis is made by showing that urinary concentration is impaired after water restriction but that there is a good response to exogenous vasopressin therapy. Nephrogenic diabetes insipidus can be identified by a patient's lack of response to AVP. Nephrogenic diabetes insipidus is caused by a familial defect, although milder forms can be acquired as a result of various forms of renal disease. Central diabetes insipidus is eminently responsive to replacement therapy, particularly with dDAVP, a long lasting analogue of AVP. Nephrogenic diabetes insipidus is best treated with a combination of thiazide diuretics as well as a diet low in sodium and protein.

Transsphenoidal hypophysectomy for disseminated carcinoma of the prostate gland. Results in 53 patients

Transsphenoidal microsurgical hypophysectomy was performed in 53 men with disseminated carcinoma (Stage IV) of the prostate gland. The mean age was 64.8 years. Forty-three of the 53 men had severe pain due to their disease. Significant pain relief was obtained following hypophysectomy, usually within 24 hours, in 39 (91%) of these 43 patients. Objective remission occurred in 16 (36%) of 45 patients in whom the follow-up review was adequate to make this decision. Although dramatic, pain relief was not permanent in every patient. Four patients died in the early postoperative period, and in one, death was directly related to the operative procedure. Significant complications included partial diabetes insipidus in 40 cases (75.5%), and cerebrospinal fluid leaks in six (11.3%). The authors conclude that hypophysectomy is an appropriate operation in patients with disseminated carcinoma of the prostate gland, particularly when pain is a significant feature of the illness. Further, the transsphenoidal microsurgical approach appears to be the operative procedure of choice for performing hypophysectomy.

Mannitol osmolar clearance in diabetes insipidus of children

A modified technique of amnnitol-induced diuresis is described, in order to assess renal concentrating ability in infants and children. The infusion of 10% mannitol in 0.9% saline avoided the hypertonic saline overload and the fluid restriction period, both badly tolerated by infants and small children. In a control group of children aged from two months to seven years, the values of T(H2O) plotted against C(OSM) allowed to calculate the adjustment curve y=0.80x0.75, r=0.98 (p is less than 0.0001). In six patients with pituitary diabetes insipidus (PDI), the test was used in order to quantify the degree of ADH deficiency and evaluate the carbamazepine and clofibrate effect, in the renal concentrating mechanism. The test was tolerated perfectly in every case, obtaining qualitative and quantitative data and avoiding the hyponatremia and hypokalemia produced by the mannitol.

1-deamino-8-D-arginine vasopressin in the treatment of central diabetes insipidus in childhood

The effectiveness of therapy with carbamazepine and clofibrate (oral therapy), intramuscular pitressin-in-oil, and intranasal 1-deamino-8-D-arginine vasopressin has been compared in 15 children with partial or complete central diabetes insipidus. Mean daily urine volume without therapy was 5.4 l and dropped to 1.1 and 1.6 l/day while receiving pitressin and DDAVP, respectively. Oral agents decreased the daily urine volume to 2.2 l in patients with partial DI, with good symptomatic control except for some nocturia. These agents had no effect in patients with complete DI and did not alter pitressin requirements. Duration of pitressin action was 24 to 36 hours with a significant incidence of hyponatremia. The duration of DDAVP effect was 8 to 20 hours, varying in individual patients. Children with partial DI required smaller doses of DDAVP and the duration of action was longer than in those with complete DI. Control of serum electrolytes was excellent using two doses per day and nocturia was eliminated. All patients who had received pitressin had growth hormone antibodies, but continued to grow normally unless there was pre-existing growth hormone deficiency. These antibodies gradually disappeared after approximately one year of therapy with oral agents or DDAVP. DDAVP did not alter growth hormone, cortisol, or prolactin levels during sleep. DDAVP is the antidiuretic therapy of choice in children with either complete or partial DI; to date, no side effects have been demonstrated.

Transsphenoidal microsurgery for pituitary tumors associated with hyperprolactinemia

The results of transsphenoidal microsurgery in treating 37 patients (30 women and seven men) with pituitary tumors associated with hyperprolactinemia are presented. Immediate (10-day) postoperative fasting prolactin levels were normal (less than 25 ng/ml) in 19 of 26 patients whose preoperative prolactin level was less than 200 ng/ml, and in only three of 11 patients in whom preoperative prolactin was greater than 200 ng/ml. Twelve of 13 patients with normal preoperative pituitary-target organ function maintained normal axes postoperatively. Thirteen other patients had preoperative deficiencies in one or more pituitary-target organ axes. Postoperatively, in these latter 13 patients, a pituitary-target organ axis that was deficient preoperatively returned to normal in six cases; there was no change in five, and there was impairment in another axis in four instances. Although gross total tumor removal was believed to be complete in 35 of 37 patients, serial postoperative prolactin determinations in four of these 35 patients indicate tumor regrowth. The authors conclude that transsphenoidal microsurgery is currently the operative procedure of choice for the majority of pituitary tumors associated with hyperprolactinemia.

Water metabolism

Total body water is finely regulated and controls of intake and output are maximally activated by small osmotic changes. Sensors in the hypothalamus invoke the fluid repletion or depletion reactions through changes in thirst, urine concentration and solute intake. Antidiuretic hormone controls urinary concentration and is released mainly in response to osmotic stimuli. However, the threshold and sensitivity of this response are affected by non osmotic stimuli. Urine concentration varies in response to antidiuretic hormone only if the distal tubule, collecting duct and hypertonic medullary interstitum are intact. The capacity to conserve or excrete water depends on the osmolar load and an efficient urinary concentrating or diluting mechanism.

Disorders of thirst are uncommon and often associated with abnormal antidiuretic hormone secretion. Disorders of urine concentration and dilution are common in illness and reflect abnormalities of antidiuretic hormone secretion or the renal mechanisms generating the osmotic gradient. When urine concentrating capacity is impaired ( true or nephrogenic diabetes insipidus) water depletion occurs only when thirst fails or access to water is denied. When urine diluting ability is impaired, water excess occurs when the osmolar load and minimum urinary osmolality generated are inadequate for the fluid intake.

Hyper-osmolality and hypo-osmolality are usually caused by abnormal water metabolism although they may be associated with abnormalities of solute metabolism. The various clinical syndromes are determined by the primary disease, and the associated fluid volume and osmolar abnormalities.

Inappropriate secretion of antidiuretic hormone. An overview of the syndrome

The syndrome of inappropriate secretion of antidiuretic hormone is characterized by production of less than maximally dilute urine in the presence of hypotonic plasma. It may be secondary to malignant disease, central nervous system disorders, or pulmonary disease, among other conditions, or it may be idiopathic. Manifestations are those of water intoxication, eg, confusion, fatigue, nausea, headache, and neurologic signs. The pathogenesis is not completely understood. Restriction of fluid intake to obtain a negative water balance is effective treatment.

Comparison of clofibrate and chlorpropamide in vasopressin-responsive diabetes insipidus

Six patients with vasopressin-responsive diabetes insipidus (DI) received clofibrate and chlorpropamide, singly and in combination. Decrease in urinary output averaged (mean +/- SEM): (1) clofibrate 2 g/day, 47% +/- 6%; (2) chlorpropamide 250 mg/day 59% +/- 5%; (3) clofibrate 2 g/day plus chlorpropamide 125 mg/day, 54% +/- 7%; (4) clofibrate 2 g/day plus chlorpropamide 250 mg/day 61% +/- 4%. Water deprivation tests before and during treatment showed significantly higher basal, final, and peak urinary osmolalities (Uosm) and lower free water clearance (CH20) on chlorpropamide, singly and in combination: clofibrate raised Uosm less but significantly decreased CH2O. Water load tests before and during treatment showed that chlorpropamide, singly and in combination, markedly decreased maximal urinary flow, maximal CH2O, percentage water load excreted, and increased minimal Uosm; clofibrate significantly decreased maximal urinary flow and CH2O only. One patient responded only to combination therapy. Chlorporpamide caused serious hypoglycemia in three of six patients. Clofibrate had no significant side effects.

Pathophysiologic and pharmacologic alterations in the release and action of ADH

The physiologic factors involved in vaseopressin (ADH) release and action are reviewed with emphasis on the interaction between osmotic and volume stimuli to the discharge of ADH. Abnormalities in reception of stimuli to ADH release, and in the impaired synthesis and release of ADH, are reviewed in relation to the causes of diabetes insipidus, and information on the biochemical changes which have been described in patients with nephrogenic diabetes insipidus is also discussed. We summarize the pathologic lesions and associated diseases found in 54 of our patients with diabetes insipidus. Criteria for establishing the diagnosis of diabetes insipdus are reviewed with emphasis on the dehydration test, including the importance of measuring plasma osmolality at the conclusion of water deprivation. Treatment of diabetes insipidus is briefly discussed with emphasis on the use of DDAVP and oral agents. The syndrome of inappropriate ADH secretion (SIADH) is reviewed including our experience with 39 patients. The differential diagnosis of SIADH, including the value of water loading and the measurement of ADH levels, is discussed. We comment on treatment of these patients including the use of investigational drugs. Lastly, we review the pharmacologic features and clinical relevance of some drugs which alter the release and action of ADH.

DDAVP in the treatment of central diabetes insipidus

DDAVP, 1-desamino-8-d-arginine-vasopressin, is a synthetic analogue of vasopressin with increased antidiuretic activity and decreased pressor activity. Whereas the antidiuretic-to-pressor ratio of arginine vasopressin is 1, the antidiuretic-to-pressor ratio of DDAVP is 4000. When administered as an intranasal spray, 5 to 20 mug of DDAVP produced eight to 20 hours of antidiuresis in patients with complete central diabetes insipidus. The minimum recommended therapeutic dose resulted in a maximum antidiuresis in most patients. No side effects of the drug were noted in clinical trials. DDAVP thus gives promise of becoming the standard treatment of severe central diabetes insipidus.

Drug treatment of hyperlipidemia

The most frequent indication for treatment of hyperlipidemia is for prevention of arteriosclerosis, a suspected but unproved benefit. The cornerstone of treatment of primary hyperlipidemia is diet; drugs may be added to, but do not replace, diet. When a drug is used with any patient, its potential benefits and hazards must be carefully weighed for the given subject. The subjects should be carefully followed and observed for side effects. Plasma lipids should be monitored during the course of treatment. Five drugs have been approved by the U.S. Food and Drug Administration for the treatment of hyperlipidemia: cholestyramine, clofibrate, nicotinic acid, sodium dextrothyroxine and beta-sitosterol. The use, the actions and the side effects of each and of several nonapproved agents are discussed.