Body Fluid Osmolality Research Articles

Osmotic and Ionic Regulation in Amphibians

Osmomineral regulation in four species of anurans from diverse habitats was studied under aquatic conditions. Ascaphus truei is aquatic, Rana pipiens is semiaquatic, Hyla regilla and Bufo boreas are terrestrial. The rate of osmosis is faster in terrestrial forms than aquatic forms. In μl cm⁻²h⁻¹ mean values were A. truei = 4.0, R. pipiens = 4.8, H. regilla = 5.6, and B. boreas = 16. Higher values reflect higher skin permeability to water and a higher osmolality of body fluids. Plasma Na⁺ is closely regulated at about 100 mM, which is over 100 times more concentrated than the pond water these species encounter in nature. Unidirectional fluxes of sodium were measured with 22Na or 24Na. At a given bath concentration of Na⁺ exchange rates were higher in the terrestrial species. Influx of Na⁺ displays saturation kinetics with increasing bath Na⁺ concentration. Over 90% of the influx is thermodynamically active. Compared with terrestrial species, aquatic species are characterized by high affinity-low capacity transport systems. Sodium efflux consists of renal and diffusive components. No exchange diffusion of Na⁺ was found. Renal efflux of Na⁺ was lower in aquatic species than terrestrial species (A. truei = 0.15, R. pipiens = 0.10, H. regilla = 0.35, B. boreas = 0.26 μM 10 g⁻¹h⁻¹). The integumentary loss of Na⁺ is a function of the transepithelial electrical potential difference which is a function of bath Na⁺ concentration. Body fluids become more electropositive to the bath by about 35 mV per decade increase in bath Na⁺ concentration. The constant field equation accurately predicts the increase in integumentary Na⁺ effux with increasing bath Na⁺ concentration. The most aquatic species, Ascaphus, had the lowest integumentary efflux (5.2 nM cm⁻²h⁻¹). Bufo, a terrestrial form, the highest (41 nM cm⁻²h⁻¹). All species maintained chloride balance in dilute baths in the face of an unfavorable electrochemical gradient. Chloride influx, measured with 36Cl, is predominantly carrier mediated, consisting of exchange diffusion and active transport in all species but B. boreas, in which exchange diffusion was absent. Eflux of Cl⁻ was lowest in Ascaphus and highest in Bufo. Renal loss was lower in aquatic species than terrestrial species (A. truei = 0.12, R. pipiens = 0.07, H. regilla = 0.22, and B. boreas = 0.16 μM 10g⁻²h⁻¹). The efflux was further partitioned into diffusive and exchange diffusive components. Permeability of the skin to Cl⁻, based on diffusive efflux, was lower for aquatic Ascaphus (0.4 × 10⁻⁸ cm s⁻¹) than for terrestrial Bufo (5 × 10⁻⁸cm s⁻¹). While anurans appear to possess common basic mechanisms for osmomineral regulation in freshwater, significant adaptive modifications have evolved which may affect distribution of species.

Serum osmolality and meal initiation in food and water-deprived rats

Blood serum osmolality values and behavioral measures were obtained from food and water-deprived and nondeprived rats. No differences were observed in osmolality values, whereas substantial differences were observed between deprived and nondeprived groups in latency and duration of eating. The majority of deprived animals ate before drinking when simultaneously presented with food and water. Body fluid osmolality does not appear to play a primary role in the initiation of eating under conditions of combined food and water deprivation.

Nonlinear Model of Body Fluid Volume and Osmolality Control System

The purpose of this research is to investigate a relatively complete model of the fluid volume and osmolality control systems in the human body including the basic nonlinearities. The work is an extension of that published by S. A. Corson and H. R. Weed, by M. Nagaska, S. Koshikawa and K. Suzuki, and by N. Z. Shapiro and DeHaven. Major emphasis is on the inclusion of nonlinear factors and on the consideration of movement of fluid between the intravascular, interstitial and intracellular compartments in dynamic equilibrium.We developed a detailed model of the hormonal feedback associated with water reabsorption in the kidneys. The model accounts for the basic control of the release, action and metabolization of antidiuretic hormone.For easier and more complete simulation of both static and dynamic nonlinearities and for better versatility and accuracy, the model is implemented on a digital computer. The computer results are compared with physiological data in response to different water loads and to dehydration to validate the accuracy of the model. Diabetes insipidus is simulated and the results compared with medical data.It is believed that this model offers analytic details and capability with accuracy not previously available. The research is being continued to include additional nonlinearities and control factors and to remove limiting approximations.

Aphagia in the presence of drinking an isosmotic NaCl solution

Rats with familial diabetes insipidus (D.I.) were exposed to liquids in which the solute was either excreted (NaCl), metabolized (glucose), or partially excreted-metabolized (milk). In the presence of an isosmotic solution where all the solvent was utilized for clearance of the solute (NaCl), rats continued to drink but displayed aphagia; decrease in the osmolality of NaCl solutions resulted in a proportional recovery of solid food ingestion. Exposure to milk resulted in hypophagia. Glucose solution did not interfere with the maintenance of eating, however, rats with D.I. did not increase their intake of glucose solution during solid food deprivation. Experimental evidence supports the view that the state of hydration as indicated by the body-fluid osmolality is essential for the maintenance of solid food ingestion. The evidence for a primary caloric regulation was doubtful.

Clinical aspects of body fluid osmolality.

A survey is presented of osmolality and its significance in metabolic functions. The osmolality of the body fluids depends both on intake of food and water and on the excretion via the kidneys and sweat glands. The osmolality of the body fluids is regulated by hormonal factors, which can be divided into osmolality-increasing and osmolality-lowering hormones. Some example are given of clinical conditions attended with disturbances of osmolality, and the principles of treatment of such conditions are outlined.

Effect of acute respiratory acidosis on arterial plasma osmolality

In anesthetized and nephrectomized dogs, acute respiratory acidosis was found to raise the arterial plasma osmolality: the latter exhibited a linear dependency toward Pa CO 2 over the range of 40–150 mm Hg ( ΔOsm/ ΔP CO 2 = 0.17 mOsm/mm Hg·kg H 2O). This indicates that a P CO 2 rise entails an overall increase of body fluid osmolality, the major part of which reflects apparently the filling of whole-body CO 2 stores. The possibility of minor osmotic redistributions of body water in connection with this phenomenon involves a disproportionately large uncertainty as to the magnitude of the transmembrane cationic exchanges generally assumed to contribute to extracellular buffering in respiratory acidosis. The finding of this new link between the acid-base balance and the water-and-electrolyte equilibrium in the organism may be of interest for the interpretation of some systemic effects of acute respiratory acidosis.

Stress induced osmotic changes as a function of deprivation state

A series of experiments determined the relationship between the internal osmotic balance of rats and the direction and magnitude of stress-induced, body-fluid osmolality (BFO) changes. The state of BFO was varied by food or water deprivation. Two forms of stress were applied: rotation or sham stomach loading. The results indicate that animals deprived of food or water failed to respond to rotation, but deprivation conditions had no influence on the BFO change induced by sham stomach loading. Although the change of BFO in response to nonspecific, stressful stimuli appeared to be in the hyperosmotic direction, the magnitude of BFO increase was a function of the severity of stress and the state of BFO.

Laboratory Tests in the Analysis of States of Dehydration

In an otherwise healthy child with acute dehydration known to be due to diarrhea or vomiting, the amount of deficit can best be estimated by accurate weight. Total serum protein and hematocrit provide a rough estimate of reduction in circulating blood volume, but calculation from these data will usually underestimate the deficit. Determination of urea nitrogen concentration helps to detect reduced glomerular filtration rate. Acid-base disturbances, most commonly metabolic acidosis, are detected by measuring pH and CO2 content (or base excess). Blood glucose should be measured to rule out diabetes mellitus, even in the absence of a suggestive history. Determination of potassium in serum is most important in the diagnosis of adrenal or renal insufficiency and in the post-acidotic phase after dehydration. Osmolality of body fluids is estimated by measuring [Na+]. Since osmolality of body fluids is normally maintained at the expense of fluid volume by the kidney and the hormones governing renal excretion of water and sodium, abnormal osmolality indicates a serious condition which has to be interpreted with the help of clinical data. In cases of abnormal renal function or of abnormal losses, as with removal of gastrointestinal fluids by suction, or excessive and prolonged diarrhea, measuring volume and composition of excreta may be essential. Because of cumulative deficits, patients with prolonged losses or inability to regulate oral intake by thirst cannot be treated without continual careful interpretation of the reports from a good laboratory.

A study of the electrochemistry and osmotic relationships of the cochlear fluids in the neonatal rat at the time of the development of the endocochlear potential.

1. Changes in the endocochlear potential between the 8th and 18th days after birth were investigated in the rat. Initially the potential was low but its magnitude increased rapidly between the 11th and 16th day. During the 13th and 14th days the rate of increase was approximately 1 mV/hr.2. The rapid potential increase arose virtually simultaneously in all three turns of the cochlea.3. Histological examination revealed the cochlea, including the hair cells of Corti's organ and the stria vascularis, to be fully mature before the period of rapid change in the endocochlear potential, apart from the cells of Claudius, whose final development coincided with the latter part of this phase.4. The endolymphatic sodium concentration (average 1.0 m-equiv/l.) had attained the very low adult level in the earliest period studied. The potassium and chloride concentrations were slightly below the normal adult levels, the result of some degree of general hypo-osmolality present at this time.5. The endolymphatic ionic concentrations remained unchanged during the phase of rapid increase in the endocochlear potential.6. The findings thus indicate that the distinctive endolymphatic ionic composition and the endocochlear potential arise largely independently and in succession during cochlear maturation.7. No differences in osmotic pressure were demonstrated between endolymph, perilymph and serum. The problems concerning the homoeostasis of the inner ear fluids do not consequently seem to be complicated by unusual hydrodynamic aspects.8. Alterations in body fluid osmolality, produced by intraperitoneal injection of water or hypertonic glycerol, were accompanied by simultaneous changes in the osmotic pressures of the inner ear fluids. Some portion of the membranes bounding the endolymphatic space is therefore considered to be freely permeable to water.9. The investigations provide no further information about the nature of the endocochlear potential, although an increase in the electrical resistance of the cochlear duct membranes is thought responsible for its appearance. The time relationships of this period support the concept that the potential is an essential feature of the mechano-electric transduction process.

Inappropriate secretion of ADH caused by obstruction of ventriculoatrial shunts.

~ ~ ALT-WASTING is a condition of hypo ~ tonicity of body fluids and continued renal excretion of excessive amounts of sodium chloride which is not caused by adrenal or pituitary disease. It has been encountered in patients with tuberculosis meningitis, 5,11,23 pulmonary tuberculosis, 26 and carcinoma of the lungs. 1,29 In this report we are concerned with cerebral salt-wasting, first reported by Peters and associates. 21,28 The mechanism of the salt-wasting syndrome was elucidated by Schwartz, et aL, 24,2~ who suggested that it was due to inappropriate secretion of the antidiuretic hormone (ADH). Under normal conditions, as body fluid tonicity decreases, secretion of ADH is stopped and water diuresis ensues, resulting in an increase of body fluid tonicity toward normal. In patients with salt-wasting, however, secretion of ADH continues in spite of lowered body fluid osmolality, and if intake of fluid is not restricted, progressive hypotonicity of body fluids and expansion of extracellular fluid occur with increased renal excretion of sodium. The mechanism of excessive sodium excretion may be related to inhibition of aldosterone secretion, caused by the expanded extracellular fluid volume, 2,16,19 increased glomerular filtration rate, 4,2~ or suppression of proximal tubular reabsorption of sodium. 3 From a number of reports, it appears that inappropriate secretion of ADH is also the basic mechanism involved in cases of cerebral salt.wasting.4.6.s.9,15,16 The two patients reported here developed inappropriate secretion of ADH and symptomatic hypotonicity during a period of obstruction of previously placed ventriculoatrial shunts. When a functioning shunt had been re-established, with presumed relief of hydro-

DANGERS TO INFANTS CAUSED BY CHANGES IN OSMOLAL CONCENTRATION

THE presence of acidemia in conditions of ventilatory insufficiency, such as asphyxia neonatorum, circulatory insufficiency, and in prematurely born infants with respiratory distress, has been well documented. Rudolph and his associates have reasoned that when pulmonary blood flow is reduced, physiologic compensation for the acidemia is impaired and a vicious circle leading to uncontrolled metabolic acidemia and possible death may result. Attempts to interrupt this process have been presented by Usher for respiratory distress syndrome and by Rudolph and Danilowicz in congenital heart disease. The approach of the use of infusions of alkali to correct the "metabolic component" of an acidemia that has an underlying basis in failure of ventilation has achieved widespread acceptance. The purpose of this paper is to call attention to an important possible risk of such therapy—hyperosmolality. In particular, the recent interest in instant repair of neonatal acidemia and the now common practice in patients of all ages of rapid repair of acidemia by NaHCO3 infusions in the management of patients undergoing cardiac surgery and of those being resuscitated have rekindled interest in the limits of tolerance for the infusion of hyperosmolal solutions. The current use of concentrated contrast materials for angiography, the intravenous use of 50% glucose solutions for neonates, and the increased use of concentrated mannitol and other hyperosmolal solutions for treatment of shock and cerebral edema constitute other clinical situations calling for a review of the underlying physiologic changes attending such therapy and emphasizing when and where serious danger exists in inducing changes in body fluid osmolality.

Urine osmolality. A definitive test of renal function.

Introduction The ability of the kidneys to concentrate urine is regarded as a sensitive indicator of renal function. 1 Since concentration tests are easily done, they enjoy wide clinical use. This renal activity is usually studied by measuring urine specific gravity, i.e. the ratio of the weight of urine to an equal volume of water. The specific gravity of a solution is dependent upon the weight of the particles making up the solution. However, specific gravity will afford only a rough index of renal concentrating ability since the kidney, in the maintenance of water and electrolyte balance, responds to changes in the osmolality of body fluids, not the specific gravity. 2 This information is only slowly penetrating clinical medicine. There have been some studies relating maximum urine osmolality to the hypertensive state, diabetes mellitus, rheumatic heart disease, 2,3 and sicklemia. 4 Some relationships between urine osmolality and urine specific gravity