Hyponatremia in the rat in the absence of positive water balance.
(17/614)
The purpose of this report is to determine the mechanisms that lead to hyponatremia when isotonic saline was the only fluid infused into rats given antidiuretic hormone (ADH), and what might minimize the degree of this hyponatremia. Normal rats were deprived of food and water for the 24-hr study period. They received an infusion of isotonic saline to expand their extracellular fluid (ECF) volume with and without exogenous ADH administration (N = 8 in each of the four groups). Similar studies were also carried out in 32 rats fed a low electrolyte diet for 72 hr before the experiment. An additional control group was fed the low electrolyte diet supplemented with sodium (Na), potassium (K), and chloride (Cl). Hyponatremia developed over 24 hr in rats fed their usual diet if treated with ADH and isotonic saline (fall, 13 +/- 2 mM, P < 0.01). The hyponatremia was caused by negative balance for Na + K salts. Hyponatremia did not develop after the saline + ADH treatment if rats were pretreated for 3 days with a low electrolyte diet. Two factors were required to develop this hyponatremia--generation of electrolyte-free water as a result of the excretion of a large quantity of Na + K salts at a high concentration in the urine, and prevention of the excretion of this electrolyte-free water by ADH. Increasing the avidity for Na reabsorption by the kidney prevented this type of hyponatremia from developing. (+info)
Kidney aquaporin-2 expression during escape from antidiuresis is not related to plasma or tissue osmolality.
(18/614)
Recent results indicate that renal escape from vasopressin-induced antidiuresis is accompanied by a marked downregulation of whole kidney aquaporin-2 (AQP-2) protein and mRNA expression. However, in those studies, the escaped animals were also markedly hypo-osmolar compared to controls as a result of water loading during antidiuresis. The present studies evaluated whether systemic or local osmolality contributes to the downregulation of AQP-2 expression in this model. In the first study, two groups of 1-deamino-[8-D-arginine]-vasopressin (dDAVP)-infused rats were water-loaded; after establishment of escape, one group was then water-restricted for 4 d to reverse the escape, whereas the other group continued daily water loading. Whole kidney AQP-2 protein was measured by Western blotting, and inner medulla AQP-2 mRNA was determined by Northern blotting. Results were compared to dDAVP-infused rats fed solid chow. After 4 d of water restriction, urine volume decreased to the same level as in the rats on solid chow; however, plasma sodium concentrations and plasma osmolality remained low. Despite maintenance of significant hypo-osmolality, rats in which escape was subsequently reversed by water restriction reestablished high dDAVP-stimulated kidney levels of AQP-2 after 4 d of water restriction. In the second study, AQP-2 expression was evaluated in different regions of kidneys from water-loaded rats undergoing escape from antidiuresis. Despite markedly different interstitial osmolalities, significant downregulation of AQP-2 expression compared to dDAVP-infused control rats was seen in the inner medulla, outer medulla, and cortex. Thus, neither systemic nor interstitial osmolality appears to appreciably be correlated with downregulation of kidney AQP-2 expression during escape from antidiuresis. These results therefore suggest that additional vasopressin- and osmolality-independent factors, likely related to the effects of extracellular fluid volume expansion, also regulate kidney AQP-2 expression in rats. (+info)
Fetal diuretic responses to maternal hyponatremia: contribution of placental sodium gradient.
(19/614)
Maternal hyponatremia induces fetal hyponatremia and increased fetal urine flow. We sought to examine the relative contributions of the placental Na(+) gradient vs. the absolute decrease in fetal plasma Na(+) in the fetal diuretic response to hyponatremia. Seven ewes with singleton fetuses (130 +/- 2 days) were prepared. Ewes received intravenous 1-desamino-8-D-arginine vasopressin (20 microg) and warm tap water (2 liters). Maternal plasma Na(+) was decreased to achieve two levels of maternal hyponatremia. Maternal and fetal blood volume were measured with radiolabeled red blood cells. In response to the first decrease in maternal plasma Na(+), fetal plasma Na(+) did not change initially. Subsequently, fetal plasma Na(+) decreased, normalizing the gradient. The second decrease in maternal plasma Na(+) similarly induced a reduced and normalized placental gradient at lower fetal plasma Na(+) values. Fetal urine flow increased in direct proportion to the degree of fetal hyponatremia (13, 38, 63, 100%, respectively). Maternal, although not fetal, blood volume significantly increased in response to hyponatremia. These results suggest that chronic fetal hyponatremia will result in a persistent diuresis, despite placental equilibration. (+info)
Syndrome of recurrent increased secretion of antidiuretic hormone following multiple doses of vincristine.
(20/614)
The syndrome of inappropriate antidiuretic hormone secretion (SIADH) has been recognized to occur following treatment with vincristine. None of the reports have provided information regarding its potential for recurrence on further challenge with vincristine (VCR), an agent generally required for repeated use in patients with malignancies. Symptomatic hyponatremia and SIADH that occurred 8 days following administration of VCR in a child with acute lymphatic leukemia was documented with specific radioimmunoassay of urinary ADH levels. The further occurrence of recurrent elevations in ADH excretion 8-10 days following repeated treatment with VCR was also observed. However, SIADH was prevented by prophylactic rigorous fluid restriction. The occurrence of SIADH following VCR therefore does not preclude the further safe usage of this drug. (+info)
Phase I study of cisplatin and docetaxel plus mitomycin C in patients with metastatic non-small cell lung cancer.
(21/614)
BACKGROUND: Docetaxel, cisplatin and mitomycin C are some of the active drugs used in the treatment of patients with metastatic non-small cell lung cancer (NSCLC). The purpose of this study was to determine the maximum tolerated dose (MTD) and recommended dose of the three drugs in combination for such patients. METHODS: Chemotherapy-native patients with metastatic NSCLC were enrolled in this study. The doses of docetaxel and cisplatin were fixed at 60 and 80 mg/m2, respectively. It was planned to increase the dose of mitomycin C from 4 to 6 and 8 mg/m2. All drugs were administered on day 1 and repeated every 3-4 weeks. RESULTS: All six patients received 60 mg/m2 of docetaxel and 80 mg/m2 of cisplatin, three of them with 4 mg/m2 of mitomycin C (level 1) and the other three with 6 mg/m2 of mitomycin C (level 2). Two of the three level 2 patients experienced dose-limiting toxicities (DLTs) in first cycle: febrile neutropenia and grade 3 hyponatremia. Based on these data, the MTD was concluded to be 60 mg/m2 for docetaxel, 80 mg/m2 for cisplatin and 6 mg/m2 for mitomycin C. Evaluation of the data from all of the cycles, however, showed that four of the six patients experienced DLTs. CONCLUSIONS: The addition of mitomycin C to docetaxel and cisplatin resulted in relatively high toxicities. It was impossible to use a high enough dose of mitomycin C to improve the survival of NSCLC patients. We therefore concluded that further evaluation of this combination is unwarranted. (+info)
Isolated corticotropin deficiency in chronic alcoholism.
(22/614)
Three patients who chronically abused alcohol were found to be hyponatraemic with normal plasma potassium. The first had been admitted with confusion and weight loss, the second with hypotension and sepsis, and the third with confusion and hypoglycaemia-induced seizures. All three patients had a subnormal cortisol response in the short synacthen test; however, the plasma cortisol after three days of tetracosactrin administration was greater than 550 nmol/L. Baseline corticotropin levels were less than 10 pg/mL in all three. No structural lesions of the hypothalamo-pituitary tract were found and there was no evidence of other endocrinopathies. Glucocorticoid replacement therapy led to the resolution of hyponatraemia and hypoglycaemia, where present, and to clinical improvement. The two surviving patients remained hypocortisolaemic in the long term, without recurrence of hyponatraemia or hypoglycaemia. The features of isolated corticotropin deficiency are easily confused with other effects of chronic alcohol abuse. In alcoholic patients with unexplained hyponatraemia, hypoglycaemia or haemodynamic instability, a short tetracosactrin test is advisable. (+info)
The treatment of hyponatraemia using vasopressin antagonists.
(23/614)
Hyponatraemia is a frequent electrolyte disorder. It is primarily attributable to vasopressin excess plus sustained fluid intake. Hyponatraemia causes CNS symptoms, especially during the first 2-4 days; these symptoms are related to brain swelling. Hyponatraemia occurs in the setting of liver cirrhosis and congestive cardiac failure, in which it is related to stimulation by low arterial blood pressure acting through baroreceptors. Hyponatraemia also occurs in the syndrome of inappropriate antidiuretic hormone secretion, usually from neoplasms releasing vasopressin. The conventional treatment of hyponatraemia used to be fluid restriction and treatment of the underlying disorder. This kind of treatment has been unreliable, cumbersome and difficult to comply with for the patient. In the future, effective vasopressin V2 antagonists will become available for clinical use in the treatment of hyponatraemia, and are expected to improve the management of hyponatraemia. Pharmacological characteristics and observations of biological effects of three antagonists are reported in the present article. (+info)
Hyponatremia and hypernatremia in the elderly.
(24/614)
Management of abnormalities in water homeostasis is frequently challenging. Because age-related changes and chronic diseases are often associated with impairment of water metabolism in elderly patients, it is absolutely essential for clinicians to be aware of the pathophysiology of hyponatremia and hypernatremia in the elderly. The sensation of thirst, renal function, concentrating abilities and hormonal modulators of salt and water balance are often impaired in the elderly, which makes such patients highly susceptible to morbid and iatrogenic events involving salt and water. Clinicians should use a systematic approach in evaluating water and sodium problems, utilizing a comprehensive history and physical examination, and a few directed laboratory tests to make the clinical diagnosis. Furthermore, clinicians should have a clear appreciation of the roles that iatrogenic interventions and lapses in nutrition and nursing care frequently play in upsetting the homeostatic balance in elderly patients, particularly those who are in longterm institutional and inpatient settings. (+info)