Biosynthesis of vasopressin in vitro and ultrastructure of a bronchogenic carcinoma. Patient with the syndrome of inappropriate secretion of antidiuretic hormone

Hyponatraemia and the syndrome of inappropriate antidiuresis (SIAD) in cancer

Hyponatraemia is a common electrolyte abnormality seen in a wide range of oncological and haematological malignancies and confers poor performance status, prolonged hospital admission and reduced overall survival, in patients with cancer. Syndrome of inappropriate antidiuresis (SIAD) is the commonest cause of hyponatraemia in malignancy and is characterised by clinical euvolaemia, low plasma osmolality and concentrated urine, with normal renal, adrenal and thyroid function. Causes of SIAD include ectopic production of vasopressin (AVP) from an underlying tumour, cancer treatments, nausea and pain. Cortisol deficiency is an important differential in the assessment of hyponatraemia, as it has an identical biochemical pattern to SIAD and is easily treatable. This is particularly relevant with the increasing use of immune checkpoint inhibitors, which can cause hypophysitis and adrenalitis, leading to cortisol deficiency. Guidelines on the management of acute, symptomatic hyponatraemia recommend 100 mL bolus of 3% saline with careful monitoring of the serum sodium to prevent overcorrection. In cases of chronic hyponatraemia, fluid restriction is recommended as first-line treatment; however, this is frequently not feasible in patients with cancer and has been shown to have limited efficacy. Vasopressin-2 receptor antagonists (vaptans) may be preferable, as they effectively increase sodium levels in SIAD and do not require fluid restriction. Active management of hyponatraemia is increasingly recognised as an important component of oncological management; correction of hyponatraemia is associated with shorter hospital stay and prolonged survival. The awareness of the impact of hyponatraemia and the positive benefits of active restoration of normonatraemia remain challenging in oncology.

Copeptin is not useful as a marker of malignant disease in the syndrome of inappropriate antidiuresis

OBJECTIVE

The syndrome of inappropriate antidiuresis (SIAD) is a common condition in hospitalized patients. It is crucial to establish the cause of SIAD, especially in order to exclude underlying malignancy. As malignant SIAD may be due to a paraneoplastic synthesis of arginine vasopressin, we hypothesized that its stable surrogate marker copeptin can be used as a diagnostic tool to differentiate between malignant and non-malignant SIAD.

METHODS

Prospective observational study. We analyzed data from 146 SIAD patients of two different cohorts from Switzerland and Germany. Patients were included while presenting at the emergency department and underwent a standardized diagnostic assessment including the measurement of copeptin levels.

RESULTS

Thirty-nine patients (median age: 63 years, 51% female) were diagnosed with cancer-related SIAD and 107 (median age: 73 years, 68% female) with non-malignant SIAD. Serum sodium levels were higher in cancer-related versus non-malignant SIAD: median (IQR) 124 mmol/l (120; 127) versus 120 mmol/l (117; 123) (P<0.001). Median (IQR) copeptin levels of patients with cancer-related SIAD were 11.1 pmol/l (5.2; 37.1) and 10.5 pmol/l (5.2; 25.2) with non-malignant SIAD (P = 0.38). Among different cancer entities, patients suffering from small-cell lung cancer showed the highest copeptin values, but overall no significant difference in copeptin levels between cancer types was observed (P = 0.46).

CONCLUSIONS

Copeptin levels are similar in cancer-related and non-malignant SIAD. Therefore, Copeptin does not seem to be suitable as a marker of malignant disease in SIAD.

Role of tolvaptan in the management of hyponatremia in patients with lung and other cancers: current data and future perspectives

Hyponatremia is the most frequently observed electrolyte abnormality in clinical practice, and its frequency is almost double in hospitalized cancer patients. As a subset of cancer, hyponatremia is quite common in lung cancer patients, and it is often coupled with the diagnosis of syndrome of inappropriate antidiuretic hormone secretion. The presence of hyponatremia is consequential in that its presence adversely affects cancer patients’ prognosis and outcomes. Limited data suggest that correcting hyponatremia in lung cancer patients can increase response to anticancer treatment, may help reduce length of hospital stay and cost, and reduce morbidity and mortality. The type of treatment for hyponatremia depends on several factors; the key factors are the duration and severity of neurological symptoms of hyponatremia and the status of extracellular volume. When hyponatremia is caused by syndrome of inappropriate antidiuretic hormone, hypertonic saline is indicated for acute symptomatic cases, whereas fluid restriction is recommended in chronic asymptomatic hyponatremia. The latter allows a slower rate of correction, thus avoiding the dreaded complication of osmotic demyelination syndrome. Fluid restriction is, however, insufficient or impractical, and often the use of pharmacological therapy such as antidiuretic hormone receptor antagonists becomes necessary. Availability of these antagonists as an effective treatment in the management of hyponatremia has been a major breakthrough, and furthermore, its clinical or investigational use in cancer-related hyponatremia may offer a potential opportunity to gain further insights into the prognostic impact of hyponatremia correction on cancer patients’ outcomes. Tolvaptan is a prototype of ADH receptor antagonists that acts at renal tubular levels to increase free water excretion without inducing major systemic electrolyte abnormalities such as hypokalemia or alkalosis. The aim of this paper is to provide a brief review while focusing on cancer hyponatremia; (1) of the epidemiology of hyponatremia and its pathophysiology and diagnostic approaches and (2) of the pharmacokinetics of tolvaptan and its clinical efficacy, safety, and compliance.

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.

The syndrome of inappropriate antidiuresis (SIAD)

Hyponatraemia is the commonest electrolyte disturbance encountered in clinical practice and the syndrome of inappropriate antidiuresis (SIADH) is the most frequent underlying disorder. There is a well-recognized relationship between hyponatraemia and increased morbidity and mortality, though it is unknown whether SIADH confers the same mortality as other causes of hyponatraemia. SIADH is the biochemical manifestation of a wide variety of diseases, and the pathophysiology of SIADH is sometimes multiple. There have been significant advances in the treatment of SIADH over the last 10 years, in particular since the introduction of the vasopressin-2 receptor antagonists, which provide a potent, disease-specific tool which targets the underlying pathophysiology of SIADH. The mechanisms and the evidence base recommendations of the available therapies for SIADH are discussed in this article. The various guidelines and recommendations for treatment of hyponatraemia all emphasise that fluid restriction is first line therapy for SIADH, but we feel that it is ineffective or unfeasible in many patients. A number of key points relevant to the use of fluid restriction are presented in the manuscript. The clinical efficacy of tolvaptan in SIADH supported by good quality randomized, placebo controlled, clinical trials. However, the cost of the therapy and the need for long term safety data may limit its widespread use. Finally, new recommendations for the management of acute hyponatraemia, with a focus on the use of bolus therapy with 3% hypertonic sodium chloride is described.

A copeptin-based classification of the osmoregulatory defects in the syndrome of inappropriate antidiuresis

Hyponatremia, the most frequent electrolyte disorder, is caused predominantly by the syndrome of inappropriate antidiuresis (SIAD). A comprehensive characterization of SIAD subtypes, defined by type of osmotic dysregulation, is lacking, but may aid in predicting therapeutic success. Here, we analyzed serial measurements of serum osmolality and serum sodium, plasma arginine vasopressin (AVP), and plasma copeptin concentrations from 50 patients with hyponatremia who underwent hypertonic saline infusion. A close correlation between copeptin concentrations and serum osmolality existed in 68 healthy controls, with a mean osmotic threshold±SD of 282±4 mOsM/kg H2O. Furthermore, saline-induced changes in copeptin concentrations correlated with changes in AVP concentrations in controls and patients. With use of copeptin concentration as a surrogate measure of AVP concentration, patients with SIAD could be grouped according to osmoregulatory defect: Ten percent of patients had grossly elevated copeptin concentrations independent of serum osmolality (type A); 14% had copeptin concentrations that increased linearly with rising serum osmolality but had abnormally low osmotic thresholds (type B); 44% had normal copeptin concentrations independent of osmolality (type C), and 12% had suppressed copeptin concentrations independent of osmolality (type D). A novel SIAD subtype discovered in 20% of patients was characterized by a linear decrease in copeptin concentrations with increasing serum osmolality (type E or "barostat reset"). In conclusion, a partial or complete loss of AVP osmoregulation occurs in patients with SIAD. Although the mechanisms underlying osmoregulatory defects in individual patients are presumably diverse, we hypothesize that treatment responses and patient outcomes will vary according to SIAD subtype.

[Historic landmarks in the study of lung cancer]

This study reviews the milestones which have been reached in the study of lung cancer, from its first early descriptions up until the end of the twentieth century. The study accompanies the birth of this new clinical entity, underlining the difficulties inherent in its diagnosis, its ever-growing increase and traces the growth of its aetiological factors, placing particular emphasis on smoking. In tandem with this, the study delves into the clinical aspects, along with new discoveries in imaging techniques and endoscopic and bioscopic techniques. It also looks at the histopathological classifications of bronchopulmonary tumours and the various staging systems which have been used over the course of time as well as the importance of mapping the disease and the different treatment weapons which have successively become available in the fight against it. The study also takes a look at the scales used in evaluating patients' physiological condition, the criteria used in evaluating response to oncostatic treatment and the role some international and national scientific societies and medical associations have played in adding to the increasing medical knowledge of lung cancer. The study clearly shows to whom we are indebted for each advance. This is a fascinating sweep of history - as is the story of all medical progress - and one we feel is important to understand, in order for us to see more clearly where we are now.

Syndrome of inappropriate antidiuresis

The syndrome of inappropriate antidiuresis is the most common cause of euvolemic hyponatremia and complicates a wide spectrum of diseases and neurosurgical conditions. The syndrome is characterized by clinical euvolemia, dilute plasma osmolality and inappropriately concentrated urine, with normal renal, adrenal and thyroid function. Hyponatremia in syndrome of inappropriate antidiuresis represents an excess of plasma water, rather than sodium deficiency. The severity of hyponatremia is limited by renal escape from antidiuresis. Treatment varies according to symptoms, severity and speed of onset of hyponatremia. Acute, severe, symptomatic hyponatremia may require rapid treatment with hypertonic saline, with care to avoid central pontine myelinosis. Chronic hyponatremia is managed with fluid restriction and demeclocycline for unresponsive cases. Vasopressin antagonists represent a new option for chronic hyponatremia of syndrome of inappropriate antidiuresis.

Small-cell lung cancer

Small-cell lung carcinoma is an aggressive form of lung cancer that is strongly associated with cigarette smoking and has a tendency for early dissemination. Increasing evidence has implicated autocrine growth loops, proto-oncogenes, and tumour-suppressor genes in its development. At presentation, the vast majority of patients are symptomatic, and imaging typically reveals a hilar mass. Pathology, in most cases of samples obtained by bronchoscopic biopsy, should be undertaken by pathologists with pulmonary expertise, with the provision of additional tissue for immunohistochemical stains as needed. Staging should aim to identify any evidence of distant disease, by imaging of the chest, upper abdomen, head, and bones as appropriate. Limited-stage disease should be treated with etoposide and cisplatin and concurrent early chest irradiation. All patients who achieve complete remission should be considered for treatment with prophylactic cranial irradiation, owing to the high frequency of brain metastases in this disease. Extensive-stage disease should be managed by combination chemotherapy, with a regimen such as etoposide and cisplatin administered for four to six cycles. Thereafter, patients with progressive or recurrent disease should be treated with additional chemotherapy. For patients who survive long term, careful monitoring for development of a second primary tumour is necessary, with further investigation and treatment as appropriate.

Downward resetting of the osmotic threshold for thirst in patients with SIADH

The syndrome of inappropriate antidiuretic hormone (SIADH) is characterized by euvolemic hyponatremia. Patients with SIADH continue to drink normal amounts of fluid, despite plasma osmolalities well below the physiological osmotic threshold for onset of thirst. The regulation of thirst has not been previously studied in SIADH. We studied the characteristics of osmotically stimulated thirst and arginine vasopressin (AVP) secretion in eight subjects with SIADH and eight healthy controls and the nonosmotic suppression of thirst and AVP during drinking in the same subjects. Subjects underwent a 2-h infusion of hypertonic (855 mmol/l) NaCl solution, followed by 30 min of free access to water. Thirst rose significantly in both SIADH (1.5 +/- 0.6 to 8.0 +/- 1.2 cm, P < 0.0001) and controls (1.8 +/- 0.8 to 8.4 +/- 1.5 cm, P < 0.0001), but the osmotic threshold for thirst was lower in SIADH (264 +/- 5.5 vs. 285.9 +/- 2.8 mosmol/kgH(2)O, P < 0.0001). SIADH subjects drank volumes of water similar to controls after cessation of the infusion (948.8 +/- 207.6 vs. 1,091 +/- 184 ml, P = 0.23). The act of drinking suppressed thirst in both SIADH and controls but did not suppress plasma AVP concentrations in SIADH compared with controls (P = 0.007). We conclude that there is downward resetting of the osmotic threshold for thirst in SIADH but that thirst responds to osmotic stimulation and is suppressed by drinking around the lowered set point. In addition, we demonstrated that drinking does not completely suppress plasma AVP in SIADH.

Endocrine paraneoplastic syndromes in lung cancer

Lung tumors are capable of synthesizing and secreting peptide proteins (hormones) that lead to a variety of endocrine paraneoplastic syndromes. Knowledge about the clinical manifestations, pathophysiology, and treatment of these syndromes has evolved over time. This article provides an up-to-date overview of this knowledge.

Endocrine and metabolic issues in the management of the chronically critically ill patient

The metabolic syndrome of chronic critical illness (CCI) consists of multisystem organ dysfunction resulting from the initial acute injury and chronic immune-neuroendocrine axis activation, adult kwashiorkor-like malnutrition, and prolonged immobilization with suppression of the PTH-vitamin D axis and hyper-resorptive metabolic bone disease. CCI patients can also present unique challenges in the management of diabetes mellitus, thyroid and adrenal diseases, electrolyte abnormalities and hypogonadism.

Systemic diseases associated with disorders of water homeostasis

Disorders of AVP secretion and action sometimes present as the first manifestation of a variety of different systemic diseases. It is prudent for the clinician to consider these causes in the differential diagnosis of hypoosmolar hyponatremia, polyuria and polydipsia, since recognizing the underlying disorder may affect treatment decisions, and intervention directed at the primary disorder often can reverse the abnormal water metabolism in these patients. Although much of the pathophysiology of these disorders is not understood completely, great progress has been made toward appreciating the complex and precise system involving thirst, AVP secretion, and renal responsiveness to AVP. Further investigation in this field likely will allow physicians to offer more effective and potent treatments in the future, such as the development of AVP V2 receptor antagonists for the treatment of SIADH [81] and edema-forming states [18, 109].

Management of small cell lung cancer

Small cell lung carcinoma typically presents as a central endobronchial lesion in chronic cigarette smokers with hilar enlargement and disseminated disease. The diagnostic pathology should be reviewed by a pathologist accomplished in reading pulmonary pathology, and, if any doubt exists in the diagnosis, additional special stains or diagnostic material should be obtained. Patients with extensive stage disease should be managed by combination chemotherapy, whereas patients with limited stage disease should be treated with etoposide/cisplatin plus concurrent chest irradiation. The chemotherapy should be administered for 4 to 6 months and then should be discontinued. Prophylactic cranial irradiation should be given to patients who achieve a complete remission. Patients should be retreated with chemotherapy if they develop a relapse of their small cell lung cancer. The patients who are followed in complete remission should be observed carefully for second cancers, and appropriate therapy should be administered if the cancer reappears.

Key peptide processing enzymes are expressed by a variant form of small-cell carcinoma of the lung

Small-cell carcinoma of the lung (SCCL) is a neuroendocrine tumor characterized by having the capacity to produce and secrete a number of small neuropeptides. These peptides serve the tumor as autocrine growth factors. SCCL is known to undergo a process of dedifferentiation to a variant (drug-resistant) form, and this process is associated with loss of marker enzymes such as neuron-specific enolase (NSE) and dopa decarboxylase (DDC). The current study was designed to discover if variant SCCL, represented by cell line NCI H82, retains some capacity to generate active neuropeptides (like vasopressin) from their precursors by continuing to express the three key classes of enzymes necessary for such conversions, namely prohormone convertases (PCs), carboxypeptidases (CPs), and peptidylglycine a-amidating monooxygenase (PAM). RT-PCR for mRNAs representing PC1, PC2, CPE, and PAM was performed on total RNA extracted from NCI H82. The primers selected for PCR and partial sequencing were synthetic 20, 21, 22, and 24 oligomers designed to yield products of 533, 880, 405, and 560 base pairs (bp) for PC1, PC2, CPE, and PAM, respectively. For the conditions used, we were able to demonstrate products for all four enzymes. Each of the four products generated were of the expected size. Cloning and sequencing of these products revealed that each had a structure identical to that published for the human form of the respective enzyme. Western analysis with antibodies against PC1, PC2, CPE, and PAM, provided evidence that mRNAs for the four enzymes are translated into proteins that could represent functional forms. Our findings therefore demonstrate that key enzymes involved in the generation of active neuropeptides, unlike the marker enzymes NSE and DDC, continue to be expressed by variant SCCL.

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.

Chronic hyponatremia due to resetting of the osmostat in a patient with gastric carcinoma

A 54-year-old schizophrenic patient who presented with hyponatremia and nephrotic-range proteinuria was subsequently discovered to have a gastric adenocarcinoma. Psychogenic water drinking, sodium depletion, and cardiac, adrenal, hepatic, and thyroid disease were excluded as causes of hyponatremia. The serum creatinine concentration was normal, and, although renal biopsy showed changes consistent with immune complex glomerulopathy, proteinuria remitted without treatment. Moderately severe hyponatremia persisted, and the diagnosis of gastric adenocarcinoma was made after the onset of early satiety 1 year later. Surgical exploration at the time of partial gastric resection revealed local metastatic lymph node involvement. Following the patient's uneventful recovery from surgery, studies of osmoregulation of vasopressin release and renal water handling were performed to determine the cause of chronic hyponatremia refractory to sodium chloride administration. Oral water loading studies revealed normal urinary diluting ability and appropriate suppression of plasma vasopressin concentrations. However, hypertonic sodium chloride infusion studies revealed a highly significant correlation between plasma osmolality and plasma vasopressin concentration, and a low osmotic threshold for vasopressin release based on linear regression analysis of the plasma vasopressin response to increasing plasma osmolality. Low osmotic threshold for vasopressin release was confirmed by exponential (log linear) and parabolic methods of data analysis. The findings in these studies are consistent with the typical features of the reset osmostat variant of the syndrome of inappropriate antidiuresis. To our knowledge, this is the first report of the occurrence of this syndrome in association with gastric adenocarcinoma.

Role played by vasopressin (and of an adrenalpostpituitary imbalance) in the development of cancerous diseases

Several authors have demonstrated that vasopressin (VP) plays a role in the metabolism of various cell lines, cancerous or not, and in particular acts upon the growth and the multiplication of cell cultures. Less known are the data concerning the existence of an adrenal-postpituitary imbalance in favour of VP in cancerous patients. Seeing that adreno-cortical hormones (ACH) are able to exert an inhibiting action on cell multiplication in vitor, a similar effect being very moderate or even absent in vivo, one can see the advantage of taking such effects into account. They allowed us to explain the discrepancy between the in vivo and in vitro effects of ACH, since VP is able to counteract the expected effects of ACH. A model, first empirical, then mathematical, of the so-called adrenal-postpituitary system, was proposed for this purpose. It enables us to propose some hypotheses in the fight to escape the action of ACH in cancer. Paradoxically, it seems that a bipolar therapy, using ACH and VP, would be useful in reaching this goal.

Hyponatremia hypo-osmolarity in neurosurgical patients. "Appropriate secretion of ADH" and "cerebral salt wasting syndrome"

This prospective study is based on 256 patients with severe brain injury. Six patients (2.3%) developed the clinical picture of inappropriate secretion of antidiuretic hormone (SIADH): 3 in the first 3 days following the injury, 3 after more than a week. Their ADH plasmatic level were measured by radio-immunoassay. In the former, many factors, largely iatrogenic, can explain the increased secretion of ADH we found and which is then definitely "appropriate". It should be prevented by fluid restriction. In the latter, we found adequately low ADH levels, when the hypo-osmolarity is taken into account. Here, the aetiology seems to be a renal salt loss, eventually in relation to a natriuric factor (e.g. atrial natriuretic factor), justifying the term: "Cerebral salt wasting syndrome". With the resistance to fluid restriction, the treatment still remains a problem.

Ectopic production of human chorionic gonadotropin by poorly differentiated transitional cell tumors of the urinary tract

We performed a 5-year histopathological review of 41 consecutive cases of transitional cell carcinoma. Of these cases 8 were positive for human chorionic gonadotropin immunoperoxidase tissue staining. All tumors were grade III and stages ranged from A to D. Three patients presented with gynecomastia as the clinical manifestation of elevated serum levels of beta-human chorionic gonadotropin. These findings document the association of this phenomenon with lesions of an aggressive nature. As with the loss of cell surface antigens, the appearance of human chorionic gonadotropin within the tumor cells may be further evidence of dedifferentiation. Human chorionic gonadotropin production may be a potential marker to gauge tumor response to chemotherapy and, perhaps, a predictor of future aggressiveness and over-all progression.

Neurosecretion of arginine vasopressin by an olfactory neuroblastoma causing reversible syndrome of antidiuresis

A 26-year-old woman with the syndrome of inappropriate antidiuresis demonstrated complete recovery following the resection of an olfactory neuroblastoma. Tissue arginine vasopressin levels by radioimmunoassay, immunohistochemical staining of the tissue arginine vasopressin, postoperative normalization of plasma arginine vasopressin levels, and the clinical resolution are evidence in support of a neurally derived tumor being the direct source of neurosecretion of arginine vasopressin rather than neurohypophyseal secretion or secretion from non-neural tissues, as reported to date in the etiology of the syndrome of inappropriate antidiuresis.

Posterior pituitary function in health and disease

This chapter has reviewed briefly the neuroanatomy relevant to the synthesis and release of AVP and OXT. Osmoregulation and baroregulation of AVP secretion has been discussed in detail, emphasizing the importance of osmotic control under normal physiological conditions. The remainder of the text has covered the two major pathophysiological disturbances of AVP secretion. In considering diabetes insipidus a pragmatic approach has been taken in the differentiation of the causes of polyuria and its treatment. A similar approach has been applied to the syndrome of inappropriate antidiuresis. Brief mention was made of the function of OXT.

The regulation of vasopressin secretion in a patient with oat cell carcinoma of the bronchus

We report a patient who had an oat cell bronchogenic carcinoma in association with the syndrome of inappropriate antidiuresis. There was an unusually long interval between the onset of hyponatraemia and clinically evident malignant disease. Dynamic testing of vasopressin secretion showed preservation of baroregulated, but not osmoregulated, vasopressin release. Immunoreactive vasopressin was detected in pleural fluid, which co-eluted with synthetic vasopressin on gel chromatography.

Management of the syndrome of inappropriate antidiuretic hormone secretion in small cell lung cancer

From 1976 to 1980, 18 of the 250 patients (7%) seen with small cell carcinoma of the lung had clinically evident inappropriate secretion of antidiuretic hormone (ADH). Hyponatremia was usually severe (116 +/- 7 meq/l), and eight patients showed symptoms of water intoxication at the time of diagnosis. Of the eight patients who had plasma ADH measured at diagnosis, seven had elevated values (mean 52.0, range 16.1 - greater than 250 pg/ml). Intensive combination chemotherapy produced objective tumor responses in all patients, and syndrome of inappropriate ADH secretion (SIADH) resolved in 16 of 17 evaluable patients within three weeks of initiation of treatment. ADH values after therapy were normal, and all patients maintained a normal serum sodium during the period of tumor remission in spite of unrestricted fluid intake. All 17 evaluable patients have developed progressive cancer, but only 10 have manifested recurrent SIADH. Patient survival was similar to the overall population of small cell carcinoma patients without SIADH. The indirect methods of treatment for SIADH (fluid restriction, demeclocycline, lithium, urea) are frequently of transient value while awaiting a response to chemotherapy or in patients with resistant tumors. However, the initial treatment of choice for SIADH associated with small cell carcinoma of the lung is combination chemotherapy.

Endocrine function in small cell undifferentiated carcinoma of the lung

The endocrine status of 106 patients with undifferentiated small cell carcinoma of the lung was evaluated before treatment was begun. Almost one half of the patients had evidence of abnormal control of the secretion of adrenal cortical steroids, manifested by loss of diurnal rhythmicity or dexamethasone suppressibility. Only two had the clinical syndrome of ectopic ACTH secretion. Evidence of inappropriate secretion of vasopressin was found in 38% of the patients, most of whom also had abnormalities of corticosteroid secretory pattern. About one half of the patients had evidence of abnormal glucose tolerance, and many also had a paradoxical rise of plasma growth hormone concentration after glucose administration. The levels of the other hormones studies were normal. The pattern of hormone abnormality observed in these patients appears to be relatively specific for small cell undifferentiated carcinoma, and is different from that observed in other pulmonary tumors. Patients with abnormal control of plasma cortisol had a worse prognosis than those with normal adrenal function, largely because of decreased response rates to chemotherapy. Other endocrine abnormalities were of no prognostic significance.

Nature of the immunoreactive neurophysins in ectopic vasopressin-producing oat cell carcinomas of the lung. Demonstration of a putative common precursor to vasopressin and neurophysin

In an attempt to delineate the nature of the immunoreactive neurophysins in oat cell carcinomas of the lung with ectopic vasopressin production, tumor neurophysins were characterized by gel filtration and by electrophoresis. In all of the five tumor tissues, activities of both vasopressin and nicotine-stimulated neurophysin (NSN) determined by radioimmunoassay were demonstrated. A small amount of oxytocin as well as estrogen-stimulated neurophysin was detected in three of the tissues. When tissue extract was subjected to Sephadex G-50 gel filtration in 0.2 N acetic acid, the major portion of immunoreactive NSN emerged in the fractions corresponding to the molecular size of 10,000. The migration pattern of NSN in these fractions on electrophoresis was qualitatively the same as that of NSN extracted from human posterior pituitary glands. In addition to this major neurophysin, immunoreactive NSN with the molecular size of 20,000 was consistently demonstrated in three tumor extracts. This high molecular weight form of neurophysin represented 6.5--8.7% of total NSN immunoactivities in each tumor extract and its elution profile was not changed when analyzed under denaturating conditions in 6 M guanidine hydrochloride. On electrophoresis, it migrated near the gamma globulin region; however, the peak was broad suggesting that it consists of more than two different molecular populations. A substantial portion of the high molecular weight NSN appears to be a glycoprotein judging from its binding to concanavalin A. When the high molecular weight from of neurophysin was incubated with trypsin, essentially all of the activities were converted into NSN with the molecular size of 10,000. Moreover, an equimolar amount of vasopressin was liberated after the treatment, the elution pattern of which closely resembled that of synthetic arginine vasopressin. When a lower concentration of trypsin was used, some of the 20,000-dalton neurophysin exhibited activities of both NSN and vasopressin. Since the antivasopressin serum used in this study appeared to be directed toward the ring portion side of vasopressin, these results suggest that this 20,000-dalton neurophysin is, in all probability, a common precursor to vasopressin and neurophysin, and that vasopressin may be located in the middle of the precursor molecule.

Abnormalities in water homeostasis in small cell anaplastic lung cancer

Forty-one patients with newly diagnosed small cell anaplastic lung cancer were evaluated for abnormalities in water homeostasis. Each patient underwent a standard water load (SWL) test. Overall, 68% had abnormalities in the SWL test. Abnormalities were found in 47% of the patients with carcinoma clinically limited to one hemithorax and in 86% of the patients with more extensive carcinoma. The determination of urinary antidiuretic hormone levels was available for 27 patients. Abnormally elevated levels were found in 44% of those patients. Forty-six patients had clinically detectable syndrome of the inappropriate secretion of antidiuretic hormone (SIADH); in 12% of patients water restriction was necessary. The incidence of detectable abnormalities in water homeostasis in this study was higher than has been previously recognized. The SWL test is a sensitive and useful means of determining the presence of impaired water handling in patients with small cell carcinoma of the lung.

Nasal neuroblastoma secreting vasopressin. A case report

A patient with a nasal neuroblastoma was found to have hypertension and severe hyponatraemia. Radiotherapy and cytotoxic chemotherapy were ineffective in reducing the size and vascularity of the neoplasm. Assay of tumor tissue post mortem revealed high levels of arginine vasopressin. The possibility of vasopressin formation to be added to the better known potential hormonal secretory activities of neuroblastomas.

Is the evidence for ectopic antidiuretic hormone watertight?

The clinical syndrome of inappropriate secretion of antidiuretic hormone (SIADH) associated with malignancy cannot be distinguished from a similar metabolic abnormality found in patients with non-malignant conditions. It is, nevertheless, widely accepted that SIADH associated with malignancy is due to the "ectopic" tumour production of arginine vasopressin (AVP). This view is challenged after scrutiny of available data. Since some malignant or non-malignant tissues may produce neurophysins, the presence of "ectopic" AVP in tumour tissue may be explained by active binding of AVP from the circulation by neurophysins. On the other hand, the absence of detectable AVP in tumour accompanied with SIADH suggests excess AVP secretion from the posterior pituitary or hyponatraemia due to other, as yet unidentified, antidiuretic factors. The concept of "ectopic" AVP may be false.

The clinical physiology of water metabolism. Part III: The water depletion (hyperosmolar) and water excess (hyposmolar) syndromes

Hyperosmolality occurs when there are defects in the two major homeostatic mechanisms required for water balance-thirst and arginine vasopressin (AVP) release. In this situation hypotonic fluids are lost in substantial quantities causing depletion of both intracellular and extracellular fluid compartments. Patients with essential hypernatremia have defective osmotically stimulated AVP release and thirst but may have intact mechanisms for AVP release following hypovolemia. Hyperosmolality can also be seen in circumstances in which impermeable solutes are present in excessive quantities in extracellular fluid. Under these conditions there is cellular dehydration and the serum sodium may actually be reduced by water drawn out of cells along an osmotic gradient. Hyposmolality and hyponatremia may be seen in a variety of clinical conditions. Salt depletion, states in which edema occurs and the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) may all produce severe dilution of body fluids resulting in serious neurologic disturbances. The differential diagnosis of these states is greatly facilitated by careful clinical assessment of extracellular fluid volume and by determination of urine sodium concentration. Treatment of the hyposmolar syndromes is contingent on the pathophysiology of the underlying disorder; hyponatremia due to salt depletion is treated with infusions of isotonic saline whereas mild hyponatremia in cirrhosis and ascites is best treated with water restriction. Severe symptomatic hyponatremia due to SIADH is treated with hypertonic saline therapy, sometimes in association with intravenous administration of furosemide. Less severe, chronic cases may be treated with dichlormethyltetracycline which blocks the action of AVP on the collecting duct.