Demeclocycline-induced nephrogenic diabetes insipidus. In-vivo and in-vitro studies

The laboratory investigation of diabetes insipidus: A review

Diabetes insipidus (DI) is a group of disorders that lead to inappropriate production of large volumes of dilute urine. The three main forms are central DI (CDI), nephrogenic DI (NDI) and primary polydipsia (PP). Differentiating CDI/NDI from PP is important as patients with true DI are at risk of severe dehydration without treatment. Biochemical testing is key in the diagnosis of DI. The indirect water deprivation test (WDT) is commonly used in the investigation of DI but has drawbacks including being cumbersome and sometimes producing equivocal results. Direct measurement of AVP has theoretical advantages but has generally only been used in specialist centres. Disadvantages include the requirement to measure AVP under hypertonic stimulation and pre-analytical/analytical challenges. Copeptin (CT-proAVP) is a proxy marker for AVP that is more stable, easier to measure and has been studied more widely in recent years. Historically, the evidence supporting the diagnostic performance of these tests has been relatively poor, being based on a few small, usually single-centre studies. However more recent, well-designed prospective studies are improving the evidence base for investigation of DI. These studies have focused on the utility of copeptin measurements during stimulation tests. There is evidence that measurement of copeptin under stimulation offers improved diagnostic performance compared to the WDT. There is currently a lack of systematic, evidence-based guidelines on the diagnosis of DI, but as the quality of the evidence defining the diagnostic performance of tests for DI continues to improve, a clearer consensus on the optimal approach should become achievable.

Syndrome of Inappropriate Antidiuresis: From Pathophysiology to Management

Hyponatremia is the most common electrolyte disorder, affecting more than 15% of patients in the hospital. Syndrome of inappropriate antidiuresis (SIAD) is the most frequent cause of hypotonic hyponatremia, mediated by nonosmotic release of arginine vasopressin (AVP, previously known as antidiuretic hormone), which acts on the renal V2 receptors to promote water retention. There are a variety of underlying causes of SIAD, including malignancy, pulmonary pathology, and central nervous system pathology. In clinical practice, the etiology of hyponatremia is frequently multifactorial and the management approach may need to evolve during treatment of a single episode. It is therefore important to regularly reassess clinical status and biochemistry, while remaining alert to potential underlying etiological factors that may become more apparent during the course of treatment. In the absence of severe symptoms requiring urgent intervention, fluid restriction (FR) is widely endorsed as the first-line treatment for SIAD in current guidelines, but there is considerable controversy regarding second-line therapy in instances where FR is unsuccessful, which occurs in around half of cases. We review the epidemiology, pathophysiology, and differential diagnosis of SIAD, and summarize recent evidence for therapeutic options beyond FR, with a focus on tolvaptan, urea, and sodium-glucose cotransporter 2 inhibitors.

Overcoming Challenges: Doxycycline as an Alternative Treatment for Hyponatremia in Managing Syndrome of Inappropriate Secretion of Anti-diuretic Hormone (SIADH) in Small Cell Lung Cancer (SCLC): A Case Report

Hyponatremia, a common complication in small cell lung cancer (SCLC), can arise from various causes such as cancer itself, its treatment, paraneoplastic syndrome-induced SIADH secretion (syndrome of inappropriate anti-diuretic hormone secretion), and brain metastasis. While fluid restriction is the initial approach, refractory cases require pharmacological intervention in managing hyponatremia secondary to SIADH. This case report presents doxycycline as an alternative treatment option for a patient with refractory hyponatremia and SCLC with brain metastases, resulting in improved serum sodium levels. However, the use of doxycycline was associated with acute pancreatitis, prompting its discontinuation without establishing a definitive causal relationship. This case report highlights the importance of alternative treatments in resource-limited settings and emphasizes personalized care for hyponatremia in SCLC patients. Doxycycline can be an option, but safety and effectiveness require further study.

Vasopressin-aquaporin-2 pathway: recent advances in understanding water balance disorders

The alteration of water balance and related disorders has emerged as being strictly linked to the state of activation of the vasopressin–aquaporin-2 (vasopressin–AQP2) pathway. The lack of responsiveness of the kidney to the vasopressin action impairs its ability to concentrate the urine, resulting in polyuria, polydipsia, and risk of severe dehydration for patients. Conversely, non-osmotic release of vasopressin is associated with an increase in water permeability in the renal collecting duct, producing water retention and increasing the circulatory blood volume. This review highlights some of the new insights and recent advances in therapeutic intervention targeting the dysfunctions in the vasopressin–AQP2 pathway causing diseases characterized by water balance disorders such as congenital nephrogenic diabetes insipidus, syndrome of inappropriate antidiuretic hormone secretion, nephrogenic syndrome of inappropriate antidiuresis, and autosomal dominant polycystic kidney disease. The recent clinical data suggest that targeting the vasopressin–AQP2 axis can provide therapeutic benefits in patients with water balance disorders.

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.

Hereditary Nephrogenic Diabetes Insipidus: Pathophysiology and Possible Treatment. An Update

Under physiological conditions, excessive loss of water through the urine is prevented by the release of the antidiuretic hormone arginine-vasopressin (AVP) from the posterior pituitary. In the kidney, AVP elicits a number of cellular responses, which converge on increasing the osmotic reabsorption of water in the collecting duct. One of the key events triggered by the binding of AVP to its type-2 receptor (AVPR2) is the exocytosis of the water channel aquaporin 2 (AQP2) at the apical membrane the principal cells of the collecting duct. Mutations of either AVPR2 or AQP2 result in a genetic disease known as nephrogenic diabetes insipidus, which is characterized by the lack of responsiveness of the collecting duct to the antidiuretic action of AVP. The affected subject, being incapable of concentrating the urine, presents marked polyuria and compensatory polydipsia and is constantly at risk of severe dehydration. The molecular bases of the disease are fully uncovered, as well as the genetic or clinical tests for a prompt diagnosis of the disease in newborns. A real cure for nephrogenic diabetes insipidus (NDI) is still missing, and the main symptoms of the disease are handled with s continuous supply of water, a restrictive diet, and nonspecific drugs. Unfortunately, the current therapeutic options are limited and only partially beneficial. Further investigation in vitro or using the available animal models of the disease, combined with clinical trials, will eventually lead to the identification of one or more targeted strategies that will improve or replace the current conventional therapy and grant NDI patients a better quality of life. Here we provide an updated overview of the genetic defects causing NDI, the most recent strategies under investigation for rescuing the activity of mutated AVPR2 or AQP2, or for bypassing defective AVPR2 signaling and restoring AQP2 plasma membrane expression.

Treatment of Severe Hypervolemic Hyponatremia in a Child With Pneumonia

A 21-month-old boy came to our attention because of pneumonia. His weight increased before presentation, and his blood test results showed hyponatremia (116 mEq/L), low plasma osmolarity (241 mOsm/L), and high urine osmolarity (435 mOsm/L). He was treated with 0.9% sodium chloride solution and intravenous furosemide, and sodium levels rose up to 135 mEq/L in 36 hours. No standard treatment is available for severe hyponatremia in children. The use of vaptans in pediatric patients is described in literature, but it lacks evidence about safety and effectiveness. We suggest that furosemide administration plus salt replacement is effective in restoring normal values of plasma sodium concentration in severe euvolemic and hypervolemic hyponatremia.

Renal aquaporins and water balance disorders

Aquaporins (AQPs) are a 13 member family (AQP0-12) of proteins that act as channels, through which water and, for some family members, glycerol, urea and other small solutes can be transported. Aquaporins are highly abundant in kidney epithelial cells where they play a critical role with respect to water balance. In this review we summarize the current knowledge with respect to the localization and function of AQPs within the kidney tubule, and their role in mammalian water homeostasis and the water balance disorders. Overviews of practical aspects with regard to differential diagnosis for some of these disorders, alongside treatment strategies are also discussed.

Mild Chronic Hyponatremia in the Ambulatory Setting: Significance and Management

Mild chronic hyponatremia, as defined by a persistent (>72 hours) plasma sodium concentration between 125 and 135 mEq/L without apparent symptoms, is common in ambulatory patients and generally perceived as being inconsequential. The association between increased mortality and hyponatremia in hospitalized patients in various settings and etiologies is widely recognized. This review analyzes the significance of mild chronic hyponatremia in ambulatory subjects and its effects on mortality and morbidity. It addresses whether this disorder should even be treated and if so, which patients are likely to benefit from treatment. The available approaches to correct hyponatremia in such patients in the context of recently published panel-generated recommendations and guidelines are described.

Evidence for the use of demeclocycline in the treatment of hyponatraemia secondary to SIADH: a systematic review

AIMS

Hyponatraemia (HN) is the most common electrolyte balance disorder in clinical practice. Since the 1970s, demeclocycline has been used in some countries to treat chronic HN secondary to syndrome of inappropriate antidiuretic hormone secretion (SIADH). The precise mechanism of action of demeclocycline is unclear, but has been linked to the induction of nephrogenic diabetes insipidus. Furthermore, the safety profile of demeclocycline is variable with an inconsistent time to onset, and a potential for complications. There has been no systematic evaluation of the use of demeclocycline for the treatment of HN secondary to SIADH to date. A systematic literature review was performed to obtain an insight into the clinical safety and efficacy of demeclocycline for this condition.

METHODS

Embase(™) , MEDLINE(®) , MEDLINE(®) In-Process, and The Cochrane Library were searched on two occasions using MeSH terms combined with free-text terms. References were screened by two independent reviewers. Relevant publications were then extracted by two independent reviewers, with a third reviewer collating and finalising extractions.

RESULTS

The searches returned a total of 705 hits. 632 abstracts were screened after the removal of duplicates. Following screening, 35 full-length publications were reviewed. Of these, 17 were excluded, resulting in 18 studies deemed relevant for data extraction. Two were randomised controlled trials (RCTs), 16 were non-RCTs, and 10 were case reports.

DISCUSSION

Although most reports suggest that demeclocycline can address serum sodium levels in specific patients with HN, efficacy is variable, and may depend upon the underlying aetiology. Demeclocycline dose adjustments can be complex, and as its use in clinical practice is not well defined, it can differ between healthcare professionals.

CONCLUSION

There is a lack of clinical and economic evidence supporting the use of demeclocycline for HN secondary to SIADH. Patients receiving demeclocycline for HN secondary to SIADH must be closely monitored.

Risk factors, complication and measures to prevent or reverse catastrophic sodium overcorrection in chronic hyponatremia

Hyponatremia is the most common electrolyte disorder encountered in clinical practice. Patients who develop this condition for more than 48 hours are at risk for severe neurological sequelae if correction of the serum sodium occurs too rapidly. Certain medical disorders are known to place patients at an increased risk for rapid correction of serum sodium concentration. Large-volume polyuria in this setting is an ominous sign. For these patients, early identification of risk factors, close monitoring of serum sodium correction and the use of 5% dextrose with or without desmopressin to prevent or reverse overcorrection are important components of treatment.

Renal aquaporins and water balance disorders

BACKGROUND

Aquaporins (AQPs) are a family of proteins that can act as water channels. Regulation of AQPs is critical to osmoregulation and the maintenance of body water homeostasis. Eight AQPs are expressed in the kidney of which five have been shown to play a role in body water balance; AQP1, AQP2, AQP3, AQP4 and AQP7. AQP2 in particular is regulated by vasopressin.

SCOPE OF REVIEW

This review summarizes our current knowledge of the underlying mechanisms of various water balance disorders and their treatment strategies.

MAJOR CONCLUSIONS

Dysfunctions of AQPs are involved in disorders associated with disturbed water homeostasis. Hyponatremia with increased AQP levels can be caused by diseases with low effective circulating blood volume, such as congestive heart failure, or osmoregulation disorders such as the syndrome of inappropriate secretion of antidiuretic hormone. Treatment consists of fluid restriction, demeclocycline and vasopressin type-2 receptor antagonists. Decreased AQP levels can lead to diabetes insipidus (DI), characterized by polyuria and polydipsia. In central DI, vasopressin production is impaired, while in gestational DI, levels of the vasopressin-degrading enzyme vasopressinase are abnormally increased. Treatment consists of the vasopressin analogue dDAVP. Nephrogenic DI is caused by the inability of the kidney to respond to vasopressin and can be congenital, but is most commonly acquired, usually due to lithium therapy. Treatment consists of sufficient fluid supply, low-solute diet and diuretics.

GENERAL SIGNIFICANCE

In recent years, our understanding of the underlying mechanisms of water balance disorders has increased enormously, which has opened up several possible new treatment strategies. This article is part of a Special Issue entitled Aquaporins.

Demeclocycline attenuates hyponatremia by reducing aquaporin-2 expression in the renal inner medulla

Binding of vasopressin to its type 2 receptor in renal collecting ducts induces cAMP signaling, transcription and translocation of aquaporin (AQP)2 water channels to the plasma membrane, and water reabsorption from the prourine. Demeclocycline is currently used to treat hyponatremia in patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Demeclocycline's mechanism of action, which is poorly understood, is studied here. In mouse cortical collecting duct (mpkCCD) cells, which exhibit deamino-8-D-arginine vasopressin (dDAVP)-dependent expression of endogenous AQP2, demeclocycline decreased AQP2 abundance and gene transcription but not its protein stability. Demeclocycline did not affect vasopressin type 2 receptor localization but decreased dDAVP-induced cAMP generation and the abundance of adenylate cyclase 3 and 5/6. The addition of exogenous cAMP partially corrected the demeclocycline effect. As in patients, demeclocycline increased urine volume, decreased urine osmolality, and reverted hyponatremia in an SIADH rat model. AQP2 and adenylate cyclase 5/6 abundances were reduced in the inner medulla but increased in the cortex and outer medulla, in the absence of any sign of toxicity. In conclusion, our in vitro and in vivo data indicate that demeclocycline mainly attenuates hyponatremia in SIADH by reducing adenylate cyclase 5/6 expression and, consequently, cAMP generation, AQP2 gene transcription, and AQP2 abundance in the renal inner medulla, coinciding with a reduced vasopressin escape response in other collecting duct segments.

Nephrogenic diabetes insipidus: essential insights into the molecular background and potential therapies for treatment

The water channel aquaporin-2 (AQP2), expressed in the kidney collecting ducts, plays a pivotal role in maintaining body water balance. The channel is regulated by the peptide hormone arginine vasopressin (AVP), which exerts its effects through the type 2 vasopressin receptor (AVPR2). Disrupted function or regulation of AQP2 or the AVPR2 results in nephrogenic diabetes insipidus (NDI), a common clinical condition of renal origin characterized by polydipsia and polyuria. Over several years, major research efforts have advanced our understanding of NDI at the genetic, cellular, molecular, and biological levels. NDI is commonly characterized as hereditary (congenital) NDI, arising from genetic mutations in the AVPR2 or AQP2; or acquired NDI, due to for exmple medical treatment or electrolyte disturbances. In this article, we provide a comprehensive overview of the genetic, cell biological, and pathophysiological causes of NDI, with emphasis on the congenital forms and the acquired forms arising from lithium and other drug therapies, acute and chronic renal failure, and disturbed levels of calcium and potassium. Additionally, we provide an overview of the exciting new treatment strategies that have been recently proposed for alleviating the symptoms of some forms of the disease and for bypassing G protein-coupled receptor signaling.

Conivaptan: a step forward in the treatment of hyponatremia?

Hyponatremia is one of the most common electrolyte abnormalities linked to adverse outcomes and increased mortality in hospitalized patients. While the differential diagnosis for hyponatremia is diverse, most cases stem from arginine vasopressin (AVP) dysregulation, where hypoosmolality fails to suppress AVP synthesis and release. The physiological effects of AVP are currently known to depend on its interaction with any of 3 receptor subtypes V1A, V2, and V1B. Activation of V2 by AVP is the key in renal water regulation and maintenance of total body volume and plasma tonicity. Despite the long-recognized problem with excess AVP in euvolemic and hypervolemic hyponatremia, traditional therapeutic options have relied on nonspecific and potentially problematic strategies. More recently, a new class of drugs, introduced as “aquaretics,” has gained great attention among clinicians because of its ability to correct hyponatremia via direct competitive inhibition of AVP at V2 receptors to induce renal electrolyte-free water excretion. In this paper, we aim to review available clinical data on the only FDA-approved aquaretic, dual V1A/V2 receptor antagonist conivaptan, discuss its clinical indications, efficacy, safety profile, and comment on its clinical limitations.

Managing hyponatremia in patients with syndrome of inappropriate antidiuretic hormone secretion

Disorders of sodium [Na+] and water metabolism are commonly encountered in the hospital setting due to the wide range of disease states that can disrupt the balanced control of water and solute intake and output. In particular, the prompt identification and appropriate management of abnormally low serum [Na+] is critical if we are to reduce the increased morbidity and mortality that accompany hyponatremia in hospitalized patients. Use of an algorithm that is based primarily on the symptomatology of hyponatremic patients, rather than the serum [Na+] or the chronicity of the hyponatremia, will help to choose the correct initial therapy in hospitalized hyponatremic patients. However, careful monitoring of serum [Na+] responses is required in all cases to adjust therapy appropriately in response to changing clinical conditions. Although this approach will enable efficacious and safe treatment of hyponatremic patients with syndrome of inappropriate antidiuretic hormone secretion (SIADH) at the present time, evolving knowledge of the consequences of chronic hyponatremia will likely alter treatment indications and guidelines in the future.

Managing hyponatremia in patients with syndrome of inappropriate antidiuretic hormone secretion

This review will address the management of hyponatremia caused by the syndrome of inappropriate antidiuretic hormone secretion (SIADH) in hospitalized patients. To do so requires an understanding of the pathogenesis and diagnosis of SIADH, as well as currently available treatment options. The review will be structured as responses to a series of questions, followed by a presentation of an algorithm for determining the most appropriate treatments for individual patients with SIADH based on their presenting symptoms.

Causes of reversible nephrogenic diabetes insipidus: A systematic review

BACKGROUND

In nephrogenic diabetes insipidus (NDI), the kidney is unable to produce concentrated urine because of the insensitivity of the distal nephron to antidiuretic hormone (arginine vasopressin). In settings in which fluid intake cannot be maintained, this may result in severe dehydration and electrolyte imbalances. The risk for conversion of reversible to irreversible NDI seems to be a potential complication. This review summarizes the reversible causes of acquired NDI to facilitate earlier recognition and more effective treatment by clinicians.

METHODS

Two reviewers independently searched MEDLINE, Experta Medica (EMBASE), and ISI bibliographic databases. Human studies that described NDI caused by drugs, substances, or metabolic disturbances were included. To evaluate the causal role of the risk factor, data were abstracted according to Koch's postulates.

RESULTS

One hundred fifty-five studies published between 1957 and March 2004 described 30 risk factors. Of 155 studies, 58 studies provided a "definite" diagnosis of NDI; 83 studies, a "probable" diagnosis; and 14 studies, a "possible" diagnosis. Nine factors were considered "definite" causes of NDI; 15 factors, "probable" causes; and 6 factors, "possible" causes. The most reported risk factors were lithium (84 studies), antibiotics (16 studies), antifungals (11 studies), antineoplastic agents (9 studies), antivirals (8 studies), and metabolic disturbances (8 studies). Duration of NDI reversal, as well as conversion to irreversible symptoms, seemed to depend on the duration of exposure.

CONCLUSION

Most risk factors for reversible NDI were medications, and their identification and removal resulted in resolution of the condition. Long-term treatment with lithium seemed to result in irreversible NDI.

Pediatric tetracycline-induced pseudotumor cerbri

BACKGROUND

Tetracyclines have long been recognized as a cause of pseudotumor cerebri in adults, but the role of tetracyclines in the pediatric age group has not been well characterized in the literature and there have been few reported cases. We present 6 cases to better delineate the problem, the patient profile, the response to treatment, and the sequelae.

METHODS

We retrospectively analyzed the records of all patients admitted with a diagnosis of pseudotumor cerebri who had documented usage of a tetracycline-class drug immediately before presentation at the Hospital For Sick Children in Toronto, Canada, from January 1, 1986, to March 1, 1996.

RESULTS

Six patients (5 female, 1 male) who met all inclusion and exclusion criteria were identified; their ages ranged from 12 to 17 years. All were being treated for acne vulgaris. Duration of use before diagnosis was as short as 2 weeks and as long as 10 months, with a mean of 4.4 months. Duration of symptoms ranged from 0.57 to 4 weeks. Symptoms included headache (6 of 6), nausea (5 of 6), and diplopia (4 of 6). All for whom height and weight data were known (5 of 6) were in the upper quartile for body mass index. Visual acuity was 6/6 in all but 1 eye of one patient (6/9) at diagnosis, and final visual acuity was 6/6 in all patients. All had normal color vision, where this was recorded (5 of 6). The only recorded field defect was enlargement of the blind spot (4 of 6). All patients responded to treatment, with loss of symptoms in 1 day to 4 weeks.

CONCLUSIONS

Pseudotumor cerebri as a result of tetracycline-class drugs does occur in the pediatric population. With prompt and appropriate medical treatment, long-term sequelae can almost always be avoided. Physicians who treat patients with tetracyclines need to be aware of the potential complications in children.

Nephrotoxicity of xenobiotics

Nephrotoxicity can be grouped by the xenobiotics place of action, by the clinical presentation or by the generic toxic effect. The latter can be dose related, indirect, idiosyncratic or allergic. Nephrotoxicity of lithium, demeclocycline, aminoglycosides, cyclosporine, mercuric ion, nonsteroidal anti-inflammatory drugs, methoxyflurane, ethylene glycol, D-penicillamine and methicillin is reviewed in light of all these three viewpoints, but emphasis is on toxic mechanisms.

A comparative study on the effects of tetracyclines and lithium on the cyclic AMP second messenger system in rat brain

1. This study was aimed at investigating the effects of demeclocycline (DMC), minocycline (MC), and lithium (Li) in vitro on cyclic AMP (cAMP) accumulation in rat cerebral cortex stimulated by noradrenaline, forskolin, and ouabain. 2. DMC, MC, and Li dose-dependently reduced noradrenaline-stimulated cAMP formation in cortical slices, but only Li inhibited the cAMP formation induced by forskolin. 3. In contrast to Li, DMC and MC did not affect noradrenaline-stimulated adenylate cyclase activity in cortical membranes. 4. In cortical slices, ouabain stimulated the cAMP production (required the presence of extracellular Ca2+ and was blocked by verapamil). Ouabain-stimulated cAMP accumulation in cortical slices was inhibited by DMC, MC, and Li. 5. DMC and MC do not seem to interact directly with the adenylate cyclase as reported for Li. It is concluded that the tetracyclines, DMC and MC, affect the cAMP signaling system in rat brain by mechanisms that differ from that of Li. The decreased receptor agonist-stimulated cAMP production in cortical slices in the presence of DMC and MC may be due to the Ca(2+)-chelating ability of these tetracyclines.

Idiopathic intracranial hypertension associated with tetracycline use in fraternal twins: case reports and review

Fraternal twin sisters developed idiopathic intracranial hypertension (IIH) shortly after beginning tetracycline for treatment of acne. We reviewed from the literature 19 familial cases of IIH and 37 cases of IIH associated with tetracycline usage. Among the 37 combined adult and pediatric cases, 26 of 37 had resolution of signs or symptoms of IIH within hours to days of stopping the antibiotic, and rapid recurrence with reinitiation of drug occurred in 4 of 37. We suggest that these cases may be tetracycline-induced, may be related to an underlying genetic susceptibility, and support the notion of multifactorial etiologies for IIH.

Vasopressin release and water metabolism in patients with cirrhosis

Water retention is a complication in many patients with cirrhosis, usually attributed to excessive release of arginine vasopressin. To investigate the responsiveness of arginine vasopressin to osmotic and non-osmotic stimuli and its relationship to free water excretion, we studied 19 patients with cirrhosis under three different conditions: 45 min with legs raised to 60 degrees, to expand the central blood volume; infusion of 1000 ml of 0.45% saline solution to reduce plasma osmolality; and rapid injection of 50 ml of 2 M NaCl to increase plasma osmolality. Both expansion of central blood volume and decrease of plasma osmolality significantly reduced plasma vasopressin levels (from 2.1 +/- 0.6 to 1.39 +/- 0.3 pg/ml, p < 0.04; and from 1.09 +/- 0.25 to 0.41 +/- 0.13 pg/ml, p < 0.0001). The changes in free water excretion differentiated two subgroups of patients during each test: excretors and non-excretors. In the excretors, increased free water excretion was associated with suppressed vasopressin levels (below 0.5 pg/ml) and normal renal function. In the non-excretors, inability to improve free water excretion was associated with high vasopressin levels or with reduced distal delivery of the glomerular filtrate, except in some cases where vasopressin levels had fallen below 0.5 pg/ml and renal function was normal. For these cases the presence of other vasopressin-independent antidiuretic mechanisms is conceivable. The injection of hypertonic saline solution caused significant rises in plasma osmolality (from 287 +/- 1.9 to 292 +/- 1.6 mmol/kg, p < 0.05) and in plasma vasopressin levels (from 1.13 +/- 0.29 to 2.86 +/- 0.52 pg/ml, p < 0.05). These results suggest that vasopressin release in patients with cirrhosis is normally responsive to osmotic and non-osmotic stimuli, although our results show a lower theoretical osmolar threshold for suppression of vasopressin release in non-excretors than in excretors (276 vs 284 mmol/kg).

Effect of desmopressin on aqueous humor flow in humans

The rate of aqueous humor flow was studied in 17 human subjects with neurogenic diabetes insipidus. Flow was measured by fluorophotometry on two consecutive afternoons. The first day, subjects used desmopressin to control their diuresis; on the second day, subjects did not use desmopressin and had uncontrolled diuresis. On both days, one eye was treated with the beta-adrenergic antagonist, timolol. With desmopressin, the rate of aqueous humor flow in the untreated eye was 2.53 +/- 0.79 microliters/min (mean +/- standard deviation) and in the timolol-treated eye was 1.69 +/- 0.40 microliters/min. Without desmopressin, the rate of aqueous humor flow in the untreated eye was 2.34 +/- 0.69 microliters/min and in the timolol-treated eye was 1.53 +/- 0.43 microliters/min. Thus, the use of desmopressin was associated with a slightly higher rate of aqueous humor flow in both the normal and the beta-adrenergically inhibited eye (P = .05), and the suppression of aqueous humor flow associated with beta-adrenergic inhibition occurred with and without antidiuretic hormone (P < .001). The observed differences in aqueous humor flow on the two days could have been caused by a direct effect on the eye or to indirect effects, such as the change in plasma osmolality, which changed from 291 +/- 6 mOsm on the desmopressin day to 299 +/- 8 mOsm on the desmopressin-abstention day (P < .001).

Central and peripheral minocycline suppresses motor activity in rats

Minocycline (MIN) HCl is a tetracycline derivative previously shown to inhibit agonist-induced accumulation of cyclic adenosine monophosphate (cAMP) in vitro and suppress motor activity and amphetamine-induced hyperactivity in rats following SC injection. The present study examined the effect of IV and intracerebral MIN on baseline activity and amphetamine-induced hyperactivity. IV MIN suppressed both types of activity in doses of 100 and 150 mg/kg. When injected ICV, MIN (50 micrograms/2 microliter) suppressed the increase in rearing elicited by amphetamine but did not affect baseline activity. MIN did not attenuate the behavioral suppression induced by the cAMP phosphodiesterase inhibitor rolipram. MIN apparently has centrally mediated effects on motor activity in rats; however, it is not yet possible to associate MIN's behavioral effects with its ability to inhibit agonist-induced stimulation of cAMP.

Transepithelial water movement in response to carbamazepine, chlorpropamide and demeclocycline in toad urinary bladder

1. Osmotic water movement across toad isolated hemibladders was measured by a gravimetric method. 2. The influence of carbamazepine, chlorpropamide and demeclocycline on the antidiuretic hormone (ADH)-induced water flow rate was examined. 3. No antidiuretic activity due to carbamazepine alone was observed but a slight inhibition due to ADH-induced water flow was observed in the presence of carbamazepine over a selected dose-range. This was unexpected and is inconsistent with data from in vivo studies in man. 4. Chlorpropamide potentiated ADH-induced water flow, in keeping with the hypothesis that chlorpropamide sensitizes the renal tubules to ADH-induced water flow. 5. Demeclocycline inhibited ADH-induced water flow. The mechanism of action remains unclear.

A review of disorders of water homeostasis in psychiatric patients

Disorders of water homeostasis are common in psychiatric patients and include compulsive water drinking, the syndrome of inappropriate antidiuretic hormone secretion (SIADH), and the syndrome of self-induced water intoxication (SIWI). Although water intoxication was recognized nearly 70 years ago, the physiological basis of these disorders of water metabolism still remains elusive. This review will provide a historical overview, critique current studies on compulsive water drinking and SIWI, discuss possible etiologies, and present current approaches to treatment of these disorders. Because of the complexity of the subject, a review of normal water homeostasis and the SIADH will be included.

Inhibition by antibiotic tetracyclines of rat cortical noradrenergic adenylate cyclase and amphetamine-induced hyperactivity

Two antibiotic tetracyclines, demeclocycline (DMC) and minocycline, share several biochemical and behavioral properties with lithium (Li). DMC inhibited both noradrenaline- and chloradenosine-sensitive cyclic AMP accumulation in rat cerebral cortical slices both in vitro and ex vivo following two weeks of chronic dietary treatment. Minocycline, a lipophilic tetracycline, produced similar results in vitro. Both DMC and minocycline reduced open-field activity levels in rats following acute treatment, four hours prior to testing. Moreover, both drugs inhibited amphetamine-induced hyperactivity in the open field. Chronic treatment with 0.4% and 0.8% dietary DMC for two weeks attenuated amphetamine hyperactivity without affecting baseline activity levels in the open field. Neither DMC nor minocycline attenuated apomorphine-induced stereotypy at doses that attenuated amphetamine hyperactivity, a profile which is similar to that of lithium. Unlike lithium, however, DMC did not reverse reserpine-induced hypoactivity.

The syndrome of inappropriate antidiuretic hormone secretion with carcinoma of the tongue

A 64-year-old male developed symptomatic recurrent syndrome of inappropriate ADH secretion in association with locally advanced squamous cell carcinoma of the tongue. His SIADH was managed successfully with saline infusion, frusemide, and maintenance treatment with demeclocycline.

The pharmacologic management of the syndrome of inappropriate secretion of antidiuretic hormone

There have been numerous treatment modalities reported in the literature concerning the acute and chronic treatment of the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Water restriction remains the mainstay of therapy. However, patient noncompliance for this regimen often makes additional treatment modalities necessary. In the long-term treatment of chronic SIADH, lithium, demeclocycline, loop diuretics, and urea are helpful, regardless of the origin of the SIADH. The use of lithium is not recommended due to the incidence of digestive, cardiac, thyroid, and central nervous system side effects, as well as the demonstrated superiority of demeclocycline. Urea and loop diuretics, although shown to be effective, have not been used clinically to the extent as demeclocyline, and are not free of adverse effects. Phenytoin is limited in its use to the treatment of SIADH secondary to abnormalities of the hypothalamic-pituitary axis, and plays no role in the treatment of tumor-induced SIADH. Demeclocyline has been shown to be effective in all types of SIADH. The lack of comparative studies of long-term treatment regimens makes the selection of a regimen of choice difficult. At this point loop diuretics or demeclocycline appear to be the regimens of choice based primarily upon case reports and relatively small comparative study patient populations. Further comparative studies are needed in an attempt to identify the most efficacious regimen with the minimal incidence of adverse effects.

Demeclocycline improves hyponatremia in chronic schizophrenics

Serum sodium concentration increased significantly in eight hyponatremic schizophrenic subjects treated with demeclocycline. The incidence of severe hyponatremic episodes was significantly reduced. The authors argue that mild impairments in urinary dilution contribute to water intoxication in most chronic psychotics who develop this syndrome. Demeclocycline may help these patients.

Demeclocycline-induced natriuresis and renal insufficiency: in vivo and in vitro studies

We examined renal function and Na+ balance in a patient with congestive heart failure who was treated with demeclocycline (DMC) on three separate occasions under strict metabolic balance conditions. Natriuresis and reversible renal insufficiency, which could not be explained solely on the basis of negative Na+ balance, developed on each occasion. In contrast to reports of an association between elevated serum DMC levels and renal insufficiency in patients with cirrhotic edema, the renal insufficiency in this patient with cardiac edema occurred in the absence of high DMC levels. Consequently, markedly elevated serum DMC levels do not appear to be a prerequisite for the development of natriuresis or renal insufficiency in edematous patients receiving this drug. In an attempt to clarify the mechanism of the natriuresis, we also examined the effects of DMC on Na+ transport in an in-vitro model system, the toad urinary bladder. DMC inhibited aldosterone-stimulated Na+ transport, but had no effect on Na+ transport when the latter was jointly stimulated by ADH and theophylline. Despite this selective inhibition of the natriferic effect of aldosterone in vitro, it is unlikely that such a mechanism completely accounts for the natriuresis observed in-vivo since the natriuresis is generally of large magnitude and is usually accompanied by some degree of kaliuresis, and DMC had no consistent effect on urinary aldosterone excretion. Consequently, other mechanisms must be sought to explain the natriuretic effect of DMC in edematous patients. Likewise, mechanisms other than negative Na+ balance (perhaps primary alterations in renal hemodynamics) must underly the development of renal insufficiency in such individuals.

Electrolyte disorders in the elderly

Normal human ageing impairs homeostatic mechanisms in such a way as to exaggerate and prolong the effects of stress. Thus, an event--pathological or traumatic--which produces a trivial change in plasma electrolytes of young people may produce major oscillations of plasma levels in the elderly, which take much longer to return to 'normal levels'. This is especially apparent with perturbations in the plasma levels of sodium and potassium, mainly due to changes in renal function and neurohumeral mechanisms which occur with increasing age. Paradoxically this does not mean that the clinician should be over-enthusiastic in attempting to correct electrolyte imbalance because, for the same reasons, the danger of over-treatment producing the opposite and equally dangerous electrolyte imbalance is ever-present. Indeed, in clinical practice most electrolyte disturbances in old age are iatrogenic in origin. Cautious patience and vigilance should be the clinical approach with elderly patients. A high index of suspicion should lead to a careful appraisal of the drug (diuretic, intravenous fluid) and environmental (dehydration) aetiology of most electrolyte disturbances in old age.

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.

Clinical implications of research on the mechanism of action of lithium

Lithium is a unique drug in its clinical profile in psychiatry. Lithium has numerous biochemical effects, but none has yet been proven to be its mode of therapeutic action. Inhibition of noradrenaline-sensitive adenylate cyclase is reviewed as the only biochemical effect of lithium shown to occur in both animals and man at therapeutic lithium concentrations. A tetracycline antibiotic, demeclocycline, also blocks noradrenaline-sensitive adenylate cyclase. A clinical trial of demeclocycline in mania would provide a test of the adenylate cyclase theory of lithium action.

Syndrome of inappropriate antidiuretic hormone secretion following dis-dichlorodiammineplatinum II in a patient with malignant thymoma

A patient with malignant thymoma is reported, in whom the syndrome of inappropriate antidiuretic hormone secretion (SIADH) occurred 36-48 hours after being given cis-Dichlorodiammineplatinum II (CPPD) with a mannitol diuresis. The SIADH was treated by fluid restriction and demeclocycline and subsided after approximately 72 hours. Subsequent courses of CPPD with mannitol diuresis were given with demeclocycline prophylactically and no untoward effects noted. The precise mechanism for the SIADH following the use of CPPD is unknown, but may be life-threatening, especially since preloading with fluid followed by forced diuresis is used when CPPD is given to avoid nephrotoxicity. The patient has survived 37 months, with 24 months of relapse-free survival following treatment with CPPD, irradiation and surgery.

Serious hyponatremia in patients with cancer: management with demeclocycline

Seventeen patients with cancer or aplastic anemia received demeclocycline as treatment for hyponatremia. Prior to demeclocycline therapy no patients showed clinical signs of fluid overload or saline depletion. In all patients inappropriately concentrated urine (mean urine osmolality = 548 mOSM/kg H2O) or increased urine content of sodium (mean urine sodium = 91 mEq/L) were documented prior to demeclocycline therapy. No patient had developed hyponatremia in association with antineoplastic drug therapy. The average serum sodium (NaS) at the time of initiation of therapy was 121 mEq/L. NaS increased in all patients despite the simultaneous administration of generous volumes of fluid. NaS exceeded 130 mEq/L and average of 3.5 days following institution of demeclocycline. Patients lost an average of 2.3 kg during demeclocycline. The toxicity noted following demeclocycline was azotemia and increased serum creatinine. Eight patients developed serum urea nitrogen (SUN) in excess of 25 mg/dl; average maximum creatinine in these eight patients was 1.9 mg/dl. Average peak creatinine in eight patients who did not develop azotemia was 0.87 mg/dl. Azotemia seemed to be correlated with simultaneous administration of other nephrotoxic agents and with administration of higher doses (1200 mg/day) of demeclocycline.