Effect of acute and chronic hypernatremia on myoinositol and sorbitol concentration in rat brain and kidney

Association of postoperative hypernatremia with outcomes after elective craniotomy

STUDY OBJECTIVE

Hypernatremia is a treatable biochemical disorder associated with significant morbidity and mortality in patients undergoing surgery. However, its impact on patients who undergo elective craniotomy is not well understood. This study aimed to investigate the prognostic implications of postoperative hypernatremia on the 30-day mortality of patients undergoing elective craniotomy.

DESIGN

Retrospective cohort study.

SETTING

The Department of Neurosurgery of a high-volume center.

PATIENTS

Adult patients undergoing elective craniotomy except those with pituitary tumors, intracerebral hemorrhage, subarachnoid hemorrhage, or traumatic brain injury.

INTERVENTIONS

None.

MEASUREMENTS

Perioperative laboratory data were collected for all study participants, including sodium levels, neutrophil count, serum albumin, lymphocyte count, and blood glucose. These measurements were obtained as part of routine clinical care and provided valuable information for data analysis.

MAIN RESULTS

Of the 10,223 identified elective craniotomy patients who met our inclusion and exclusion criteria, 14.9% (1519) developed postoperative hypernatremia. This population's overall postoperative 30-day mortality rate was 1.7% (175). After performing an adjusted logistic regression analysis, we found that the odds of 30-day mortality increased gradually with increasing severity of hypernatremia: 2.9 deaths (OR, 3.79; 95% CI, 2.46-5.85) in patients with mild hypernatremia, 13.9 deaths (OR, 17.73; 95% CI, 11.17-28.12) in those with moderate hypernatremia, and 38.3 deaths (OR, 67.00; 95% CI, 40.44-111.00) in those with severe hypernatremia.

CONCLUSIONS

Hypernatremia is common after elective craniotomy, and its presence is associated with increased mortality and complications, particularly in cases of severe hypernatremia. These results emphasize the significance of risk evaluation in neurosurgical patients and propose the advantages of closely monitoring serum sodium levels in high-risk individuals. Future randomized controlled trials could provide more insight into the effect of treating postoperative hypernatremia in these patients.

Donor hypernatremia is associated with increased mortality after heart transplantation: A retrospective study

BACKGROUND AND AIMS

Donor hypernatremia has been associated with primary graft dysfunction in heart transplantation (HTx) and is correlated with impaired outcome following liver and renal transplantation. However, controversial data exist regarding the impact of sodium dysregulation on survival. This study aims to investigate the impact of donor sodium levels on early morbidity and short- and midterm survival following HTx.

METHODS

Between September 2010 and June 2021, a total of n = 218 patients underwent HTx in our center. From those, 214 could be included retrospectively in our study. For each donor, sodium levels were collected and different cut-off levels from 145 to 159 mmol/L were investigated by Kaplan-Meier-analysis. Then, recipients were divided in three groups regarding donor sodium: Normonatremia (133-145 mmol/L, n = 73), mild hypernatremia (146-156 mmol/L, n = 105) and severe hypernatremia (>156 mmol/L, n = 35). Recipient and donor variables were reviewed and compared, including peri- and postoperative characteristics and recipient survival after up to 5 years after transplantation.

RESULTS

All patients were comparable regarding baseline characteristics and perioperative parameters. Regarding early mortality, 90-day survival was significantly reduced only in patients with severe donor hypernatremia in comparison to normonatremia (90% vs. 71%, p = .02), but not in mild hypernatremia (89%, p = .89). One-year survival was comparable in all groups (p > .28).

CONCLUSION

Severe donor hypernatremia was associated with reduced short-term survival, while the correlation weakens > 1 year after HTx. As our study is limited due to the nature of its retrospective, single-center approach, future prospective studies are needed to evaluate the importance of donor management with regard to hypernatremia.

Cell Volume Control in Healthy Brain and Neuropathologies

Regulation of cellular volume is a critical homeostatic process that is intimately linked to ionic and osmotic balance in the brain tissue. Because the brain is encased in the rigid skull and has a very complex cellular architecture, even minute changes in the volume of extracellular and intracellular compartments have a very strong impact on tissue excitability and function. The failure of cell volume control is a major feature of several neuropathologies, such as hyponatremia, stroke, epilepsy, hyperammonemia, and others. There is strong evidence that such dysregulation, especially uncontrolled cell swelling, plays a major role in adverse pathological outcomes. To protect themselves, brain cells utilize a variety of mechanisms to maintain their optimal volume, primarily by releasing or taking in ions and small organic molecules through diverse volume-sensitive ion channels and transporters. In principle, the mechanisms of cell volume regulation are not unique to the brain and share many commonalities with other tissues. However, because ions and some organic osmolytes (e.g., major amino acid neurotransmitters) have a strong impact on neuronal excitability, cell volume regulation in the brain is a surprisingly treacherous process, which may cause more harm than good. This topical review covers the established and emerging information in this rapidly developing area of physiology.

The Impact of Venoarterial and Venovenous Extracorporeal Membrane Oxygenation on Cerebral Metabolism in the Newborn Brain

Background

Extracorporeal membrane oxygenation (ECMO) is an effective therapy for supporting infants with reversible cardiopulmonary failure. Still, survivors are at risk for long-term neurodevelopmental impairments, the cause of which is not fully understood.

Objective

To elucidate the effects of ECMO on the newborn brain. We hypothesized that the cerebral metabolic profile of neonates who received ECMO would differ from neonates who did not receive ECMO. To address this, we used magnetic resonance spectroscopy (¹H-MRS) to investigate the effects of venoarterial and venovenous ECMO on cerebral metabolism.

Methods

41 neonates treated with ECMO were contrasted to 38 age-matched neonates.

Results

All ¹H-MRS data were acquired from standardized grey matter and white matter regions of interest using a short-echo (TE = 35 milliseconds), point-resolved spectroscopy sequence (PRESS) and quantitated using LCModel. Metabolite concentrations (mmol/kg) were compared across groups using multivariate analysis of covariance. Elevated creatine (p = 0.002) and choline (p = 0.005) concentrations were observed in the grey matter among neonates treated with ECMO relative to the reference group. Likewise, choline concentrations were elevated in the white matter (p = 0.003) while glutamate was reduced (p = 0.03). Contrasts between ECMO groups revealed lower osmolite concentrations (e.g. myoinositol) among the venovenous ECMO group.

Conclusion

Neonates who underwent ECMO were found to have an abnormal cerebral metabolic profile, with the pattern of abnormalities suggestive of an underlying inflammatory process. Additionally, neonates who underwent venovenous ECMO had low cerebral osmolite concentrations as seen in vasogenic edema.

Hypertonicity: Pathophysiologic Concept and Experimental Studies

Disturbances in tonicity (effective osmolarity) are the major clinical disorders affecting cell volume. Cell shrinking secondary to hypertonicity causes severe clinical manifestations and even death. Quantitative management of hypertonic disorders is based on formulas computing the volume of hypotonic fluids required to correct a given level of hypertonicity. These formulas have limitations. The major limitation of the predictive formulas is that they represent closed system calculations and have been tested in anuric animals. Consequently, the formulas do not account for ongoing fluid losses during development or treatment of the hypertonic disorders. In addition, early comparisons of serum osmolality changes predicted by these formulas and observed in animals infused with hypertonic solutions clearly demonstrated that hypertonicity creates new intracellular solutes causing rises in serum osmolality higher than those predicted by the formulas. The mechanisms and types of intracellular solutes generated by hypertonicity and the effects of the solutes have been studied extensively in recent times. The solutes accumulated intracellularly in hypertonic states have potentially major adverse effects on the outcomes of treatment of these states. When hypertonicity was produced by the infusion of hypertonic sodium chloride solutions, the predicted and observed changes in serum sodium concentration were equal. This finding justifies the use of the predictive formulas in the management of hypernatremic states.

Hypertonicity: Pathophysiologic Concept and Experimental Studies

Disturbances in tonicity (effective osmolarity) are the major clinical disorders affecting cell volume. Cell shrinking secondary to hypertonicity causes severe clinical manifestations and even death. Quantitative management of hypertonic disorders is based on formulas computing the volume of hypotonic fluids required to correct a given level of hypertonicity. These formulas have limitations. The major limitation of the predictive formulas is that they represent closed system calculations and have been tested in anuric animals. Consequently, the formulas do not account for ongoing fluid losses during development or treatment of the hypertonic disorders. In addition, early comparisons of serum osmolality changes predicted by these formulas and observed in animals infused with hypertonic solutions clearly demonstrated that hypertonicity creates new intracellular solutes causing rises in serum osmolality higher than those predicted by the formulas. The mechanisms and types of intracellular solutes generated by hypertonicity and the effects of the solutes have been studied extensively in recent times. The solutes accumulated intracellularly in hypertonic states have potentially major adverse effects on the outcomes of treatment of these states. When hypertonicity was produced by the infusion of hypertonic sodium chloride solutions, the predicted and observed changes in serum sodium concentration were equal. This finding justifies the use of the predictive formulas in the management of hypernatremic states.

In vivo longitudinal proton magnetic resonance spectroscopy on neonatal hypoxic-ischemic rat brain injury: Neuroprotective effects of acetyl-L-carnitine

PURPOSE

This study evaluated the longitudinal metabolic alterations after neonatal hypoxia-ischemia (HI) in rats and tested the neuroprotective effect of acetyl-L-carnitine (ALCAR) using in vivo proton short-TE Point-RESolved Spectroscopy method.

METHODS

Rice-Vannucci model was used on 7-day-old Sprague-Dawley rats. Data were acquired from contralateral and ipsilateral cortex and hippocampus, respectively at 4 time points (24-h, 72-h, 7-days, 28-days) post-HI. The effect of subcutaneous administration of ALCAR (100 mg/kg) immediately after HI, at 4-h, 24-h, and 48-h post-HI was determined.

RESULTS

Significant reductions in glutathione (P < 0.005), myo-inositol (P < 0.002), taurine (P < 0.001), and total creatine (P < 0.005) were observed at 24-h postinjury compared with the control group in the ipsilateral hippocampus of the HI rat pups. ALCAR-treated-HI rats had lower levels of lactate and maintained total creatine at 24-h and had smaller lesion size compared with the HI only rats.

CONCLUSION

Severe oxidative, osmotic stress, impaired phosphorylation, and a preference for anaerobic glycolysis were found in the ipsilateral hippocampus in the HI pups at 24-h postinjury. ALCAR appeared to have a neuroprotective effect if administered early after HI by serving as an energy substrate and promote oxidative cerebral energy producing and minimize anaerobic glycolysis.

Neurochemical analysis of primary motor cortex in chronic low back pain

The involvement of the primary motor cortex (M1) in chronic low back pain (LBP) is a relatively new concept. Decreased M1 excitability and an analgesic effect after M1 stimulation have been recently reported. However, the neurochemical changes underlying these functional M1 changes are unknown. The current study investigated whether neurochemicals specific to neurons and glial cells in both right and left M1 are altered. N-Acetylaspartate (NAA) and myo-inositol (mI) were measured with proton magnetic resonance spectroscopy in 19 subjects with chronic LBP and 14 healthy controls. We also examined correlations among neurochemicals within and between M1 and relationships between neurochemical concentrations and clinical features of pain. Right M1 NAA was lower in subjects with LBP compared to controls (p = 0.008). Left M1 NAA and mI were not significantly different between LBP and control groups. Correlations between neurochemical concentrations across M1s were different between groups (p = 0.008). There were no significant correlations between M1 neurochemicals and pain characteristics. These findings provide preliminary evidence of neuronal depression and altered neuronal-glial interactions across M1 in chronic LBP.

Tilapia (Oreochromis mossambicus) brain cells respond to hyperosmotic challenge by inducing myo-inositol biosynthesis

This study aimed to determine the regulation of the de novo myo-inositol biosynthetic (MIB) pathway in Mozambique tilapia (Oreochromis mossambicus) brain following acute (25 ppt) and chronic (30, 60 and 90 ppt) salinity acclimations. The MIB pathway plays an important role in accumulating the compatible osmolyte, myo-inositol, in cells in response to hyperosmotic challenge and consists of two enzymes, myo-inositol phosphate synthase and inositol monophosphatase. In tilapia brain, MIB enzyme transcriptional regulation was found to robustly increase in a time (acute acclimation) or dose (chronic acclimation) dependent manner. Blood plasma osmolality and Na(+) and Cl(-) concentrations were also measured and significantly increased in response to both acute and chronic salinity challenges. Interestingly, highly significant positive correlations were found between MIB enzyme mRNA and blood plasma osmolality in both acute and chronic salinity acclimations. Additionally, a mass spectrometry assay was established and used to quantify total myo-inositol concentration in tilapia brain, which closely mirrored the hyperosmotic MIB pathway induction. Thus, myo-inositol is a major compatible osmolyte that is accumulated in brain cells when exposed to acute and chronic hyperosmotic challenge. These data show that the MIB pathway is highly induced in response to environmental salinity challenge in tilapia brain and that this induction is likely prompted by increases in blood plasma osmolality. Because the MIB pathway uses glucose-6-phosphate as a substrate and large amounts of myo-inositol are being synthesized, our data also illustrate that the MIB pathway likely contributes to the high energetic demand posed by salinity challenge.

Metabolic changes in concussed American football players during the acute and chronic post-injury phases

Background

Despite negative neuroimaging findings many athletes display neurophysiological alterations and post-concussion symptoms that may be attributable to neurometabolic alterations.

Methods

The present study investigated the effects of sports concussion on brain metabolism using ¹H-MR Spectroscopy by comparing a group of 10 non-concussed athletes with a group of 10 concussed athletes of the same age (mean: 22.5 years) and education (mean: 16 years) within both the acute and chronic post-injury phases. All athletes were scanned 1-6 days post-concussion and again 6-months later in a 3T Siemens MRI.

Results

Concussed athletes demonstrated neurometabolic impairment in prefrontal and motor (M1) cortices in the acute phase where NAA:Cr levels remained depressed relative to controls. There was some recovery observed in the chronic phase where Glu:Cr levels returned to those of control athletes; however, there was a pathological increase of m-I:Cr levels in M1 that was only present in the chronic phase.

Conclusions

These results confirm cortical neurometabolic changes in the acute post-concussion phase as well as recovery and continued metabolic abnormalities in the chronic phase. The results indicate that complex pathophysiological processes differ depending on the post-injury phase and the neurometabolite in question.

Primary motor cortex in stroke: a functional MRI-guided proton MR spectroscopic study

BACKGROUND AND PURPOSE

Our goal was to investigate whether certain metabolites, specific to neurons, glial cells, or the neuronal-glial neurotransmission system, in primary motor cortices (M1), are altered and correlated with clinical motor severity in chronic stroke.

METHODS

Fourteen survivors of a single ischemic stroke located outside the M1 and 14 age-matched healthy control subjects were included. At >6 months after stroke, N-acetylaspartate, myo-inositol, and glutamate/glutamine were measured using proton magnetic resonance spectroscopic imaging (in-plane resolution=5×5 mm(2)) in radiologically normal-appearing gray matter of the hand representation area, identified by functional MRI, in each M1. Metabolite concentrations and analyses of metabolite correlations within M1 were determined. Relationships between metabolite concentrations and arm motor impairment were also evaluated.

RESULTS

The stroke survivors showed lower N-acetylaspartate and higher myo-inositol across ipsilesional and contralesional M1 compared with control subjects. Significant correlations between N-acetylaspartate and glutamate/glutamine were found in either M1. Ipsilesional N-acetylaspartate and glutamate/glutamine were positively correlated with arm motor impairment and contralesional N-acetylaspartate with time after stroke.

CONCLUSIONS

Our preliminary data demonstrated significant alterations of neuronal-glial interactions in spared M1 with the ipsilesional alterations related to stroke severity and contralesional alterations to stroke duration. Thus, MR spectroscopy might be a sensitive method to quantify relevant metabolite changes after stroke and consequently increase our knowledge of the factors leading from these changes in spared motor cortex to motor impairment after stroke.

Myo-inositol: a marker of reactive astrogliosis in glial tumors?

In a prospective study, two-dimensional (1)H-MRS with TE of 30 ms was performed before surgery in 56 patients with glial brain tumors. Concentrations of myo-inositol (MI), trimethylamine (TMA) and creatine/phosphocreatine (tCr) were evaluated for the whole tumor and scaled to the normal-appearing contralateral brain tissue. To assign changes in MI to specific tissue pathology, the normalized peak and mean concentrations of MI were correlated with TMA and tCr concentrations. TMA is accepted as a marker of proliferating tumor tissue, and tCr might be a marker of reactive astrogliosis. The mean and peak concentrations of MI and tCr correlated positively (r = 0.7), but not the concentrations of MI and TMA. The absolute concentration of MI was significantly increased in all tumor tissues (5.55 +/- 2.92 mM; mean +/- SD) compared with the normal-appearing white matter (4.33 +/- 1.22 mM, p = 0.005), with the highest concentrations for gliomatoses (n = 10) and grade II oligoastrocytomas (n = 3). Significant differences (P = 0.004) between low- and high-grade astrocytomas were found for TMA (1.67 +/- 0.32 mM and 2.65 +/- 0.86 mM, respectively), but not for MI (5.92 +/- 1.98 mM and 5.49 +/- 3.27 mM, respectively). As increased MI and tCr concentrations were found in gliomatosis and other cerebral diseases associated with marked astrogliosis, this process may also be responsible for the observed changes in MI in other glial tumors.

Altered cerebral glucose and acetate metabolism in succinic semialdehyde dehydrogenase-deficient mice: evidence for glial dysfunction and reduced glutamate/glutamine cycling

Succinic semialdehyde dehydrogenase (SSADH) catalyzes the NADP-dependent oxidation of succinic semialdehyde to succinate, the final step of the GABA shunt pathway. SSADH deficiency in humans is associated with excessive elevation of GABA and gamma-hydroxybutyrate (GHB). Recent studies of SSADH-null mice show that elevated GABA and GHB are accompanied by reduced glutamine, a known precursor of the neurotransmitters glutamate and GABA. In this study, cerebral metabolism was investigated in urethane-anesthetized SSADH-null and wild-type 17-day-old mice by intraperitoneal infusion of [1,6-(13)C(2)]glucose or [2-(13)C]acetate for different periods. Cortical extracts were prepared and measured using high-resolution (1)H-[(13)C] NMR spectroscopy. Compared with wild-type, levels of GABA, GHB, aspartate, and alanine were significantly higher in SSADH-null cortex, whereas glutamate, glutamine, and taurine were lower. (13)C Labeling from [1,6-(13)C(2)]glucose, which is metabolized in neurons and glia, was significantly lower (expressed as mumol of (13)C incorporated per gram of brain tissue) for glutamate-(C4,C3), glutamine-C4, succinate-(C3/2), and aspartate-C3 in SSADH-null cortex, whereas Ala-C3 was higher and GABA-C2 unchanged. (13)C Labeling from [2-(13)C]acetate, a glial substrate, was lower mainly in glutamine-C4 and glutamate-(C4,C3). GHB was labeled by both substrates in SSADH-null mice consistent with GABA as precursor. Our findings indicate that SSADH deficiency is associated with major alterations in glutamate and glutamine metabolism in glia and neurons with surprisingly lesser effects on GABA synthesis.

[Controlled hypernatremia]

Hypernatremia exerts its main effect on the brain through the osmotic gradient it creates on either side of the blood brain barrier, which is impermeable to sodium. This generates a transfer of water from the intracellular to the vascular sector leading to temporary cell shrinkage. Osmoregulation permits cerebral cells to accumulate osmoactive molecules in order to restore their initial volume. It has been demonstrated in animals with brain injury that intracellular dehydration occurs essentially in the nonlesioned hemisphere. In most experimental studies, the reduction in cerebral volume obtained by hypertonic saline (HS) perfusion is accompanied by an intracranial pressure decrease, even under hemorrhagic shock conditions. Initially, clinical studies successfully used HS, as an alternative to mannitol, in the treatment of acute and refractory intracranial hypertension. Then continuous infusion of HS, with the objective of inducing hypernatremia, had produced encouraging effects on intracranial pressure control. However, these results were limited to non-randomized studies, without control groups and mainly in pediatric patients. Nevertheless, the use of HS on intracranial hypertension, refractory to conventional treatments, could be reasonable under strict monitoring of natremia as well as its adverse effects.

Proton spectroscopy detected myoinositol in children with traumatic brain injury

Previous studies have shown that proton magnetic resonance spectroscopy (MRS) is useful in predicting neurologic prognosis in children with traumatic brain injury (TBI). Reductions in N-acetyl derived metabolites and presence of lactate have been predictive of poor outcomes. We examined another spectroscopy metabolite, myoinositol (mI), to determine whether it is altered after TBI. Found primarily in astrocytes, mI functions as an osmolyte and is involved in hormone response pathways and protein-kinase C activation. Myoinositol is elevated in the newborn brain and is increased in a variety of diseases. We studied 38 children (mean age 11 y; range 1.6-17 y) with TBI using quantitative short echo time occipital gray and parietal white matter proton MRS at a mean of 7 d (range 1-17 d) after injury. We found that occipital gray matter mI levels were increased in children with TBI (4.30 +/- 0.73) compared with controls (3.53 +/- 0.48; p = 0.003). We also found that patients with poor outcomes 6-12 mo after injury had higher mI levels (4.78 +/- 0.68) than patients with good outcomes (4.15 +/- 0.69; p < 0.05). Myoinositol is elevated after pediatric TBI and is associated with a poor neurologic outcome. The reasons for its elevation remain unclear but may be due to astrogliosis or to a disturbance in osmotic function.

Activation of muscarinic cholinergic receptors enhances the volume-sensitive efflux of myo-inositol from SH-SY5Y neuroblastoma cells

A mechanism used by cells to regulate their volume under hypo-osmotic conditions is the release of organic osmolytes, one of which is myo-inositol. The possibility that activation of phospholipase-C-linked receptors can regulate this process has been examined for SH-SY5Y neuroblastoma cells. Incubation of cells with hypo-osmolar buffers (160-250 mOsm) led to a biphasic release of inositol which persisted for up to 4 h and could be inhibited by inclusion of anion channel blockers - results which indicate the involvement of a volume-sensitive organic anion channel. Inclusion of oxotremorine-M, a muscarinic cholinergic agonist, resulted in a marked increase (80-100%) in inositol efflux under hypo-osmotic, but not isotonic, conditions. This enhanced release, which was observed under all conditions of hypo-osmolarity tested, could be prevented by inclusion of atropine. Incubation of the cells with either the calcium ionophore, ionomycin, or the phorbol ester, phorbol 12-myristate 13-acetate, partially mimicked the stimulatory effect of muscarinic receptor activation when added singly, and fully when added together. The ability of oxotremorine-M to facilitate inositol release was inhibited by removal of extracellular calcium, depletion of intracellular calcium or down-regulation of protein kinase C. These results indicate that activation of muscarinic cholinergic receptors can regulate osmolyte release in this cell line.

Extracellular glutamate and other amino acids in experimental intracerebral hemorrhage: an in vivo microdialysis study

OBJECTIVE

To determine whether extracellular concentrations of glutamate and other amino acids are significantly elevated after intracerebral hemorrhage and, if so, the temporal characteristics of these changes. Although the role of excitotoxic amino acids, particularly that of glutamate, has been described in ischemic stroke and head trauma, no information exists regarding their possible contribution to the pathogenesis of neuronal injury in intracerebral hemorrhage.

DESIGN

Prospective, controlled, laboratory trial.

SETTINGS

Animal research laboratory.

SUBJECTS

Sixteen anesthetized New Zealand rabbits.

INTERVENTION

We introduced intracerebral hemorrhage in each of eight anesthetized New Zealand rabbits by injecting 0.4 mL of autologous blood under arterial pressure into the deep gray matter of the cerebrum.

MEASUREMENTS AND MAIN RESULTS

Extracellular fluid samples were collected from the perihematoma region and contralateral (right) hemisphere by in vivo microdialysis at 30-min intervals for 6 hrs. Corresponding samples were similarly collected from both hemispheres in each of eight control animals that underwent needle placement without introduction of a hematoma. Concentrations of amino acids (glutamate, aspartate, asparagine, glycine, taurine, and gamma-aminobutyric acid) in the samples were measured by use of high-pressure liquid chromatography with fluorescence detection. Glutamate concentrations (mean +/- sem) were significantly higher in the hemisphere ipsilateral to the hematoma than in the contralateral hemisphere (92 +/- 22 pg/microL vs. 22 +/- 6 pg/microL) at 30 mins after hematoma creation. A significant increase was observed at 30 mins posthematoma creation in the hemisphere ipsilateral to the hematoma compared with the baseline value. A nonsignificant increase in glutamate concentration persisted in the hemisphere ipsilateral to the hematoma, ranging from 134% to 187% of baseline value between 1 and 5 hrs after hematoma creation. In the hemisphere ipsilateral to the hematoma, a three-fold increase in the concentration of glycine was observed at 30 mins after hematoma creation compared with the baseline level (890 +/- 251 pg/microL vs. 291 +/- 73 pg/microL). There was a significant difference between the hemisphere ipsilateral to the hematoma compared with the ipsilateral (corresponding) hemisphere of the control group at 30 mins posthematoma (890 +/- 251 pg/microL vs. 248 +/- 66 pg/microL). A similar transient increase was observed in taurine and asparagine concentrations at 30 mins after hematoma creation, compared with baseline measurements. Taurine concentrations in the hemisphere ipsilateral to the hematoma were significantly higher than the ipsilateral hemisphere of the control group (622 +/- 180 pg/microL vs. 202 +/- 64 pg/microL) at 30 mins after hematoma creation.

CONCLUSIONS

The present study suggests that glutamate and other amino acids accumulate transiently in extracellular fluids in the perihematoma region during the early period of intracerebral hemorrhage. The exact role of these amino acids in the pathogenesis of neuronal injury observed in intracerebral hemorrhage needs to be defined.

Osmotic stress increases cullin-5 (cul-5) mRNA in the rat cerebral cortex, hypothalamus and kidney

Cullin-5 (cul-5), a member of the cullin gene family, may have a role in proteolysis and cell cycle regulation. Our recent study demonstrated that cul-5 mRNA is ubiquitously expressed in the central nervous system and many peripheral organs. The present study used quantitative realtime polymerase chain reaction to measure changes in cul-5 mRNA expression as a consequence of osmotic stress in vivo. Cul-5 mRNA levels were significantly increased in the rat cerebral cortex, hypothalamus and kidney following 48 h of water deprivation. Water deprivation for a shorter time period (24 h) or rehydration (24 h access to water following 48 h of water deprivation) also elevated kidney cul-5 mRNA levels. Water deprivation did not significantly alter cul-5 mRNA levels in the brainstem, cerebellum, hippocampus, lung or liver. Since cul-5 appears to be linked to proteosome-mediated protein degradation, it may have a role in protein regulation under conditions of osmotic stress.

Systemic osmotic manipulations modulate ethanol-induced taurine release: a brain microdialysis study

In recent microdialysis studies, increased extracellular concentrations of taurine after high ethanol dose administration were identified in various rat brain regions. The mechanisms by which ethanol caused these increases in extracellular taurine concentration remained unclear but could be related to ethanol-induced cell swelling. The aim of the current study was to investigate whether changes in the body osmotic state modulate the effects of ethanol on brain extracellular taurine concentrations. In several groups of rats, brain hypoosmotic or hyperosmotic states were superimposed on acute ethanol (2.0-g/kg) injections, and extracellular taurine concentrations within the nucleus accumbens were assessed by using an intracerebral microdialysis procedure. A hypoosmotic state was obtained by systemic administration of water while hyperosmotic states were induced by intraperitoneal injections of hypertonic saline solutions (1.8% or 3.6% saline). In isoosmotic conditions, ethanol induced an immediate and significant increase in taurine microdialysate content, confirming results of previous studies. However, the effects of ethanol on taurine concentrations were modulated by osmotic manipulations. Hypoosmotic conditions significantly potentiated ethanol-induced taurine release. In contrast, ethanol-induced increases in extracellular taurine levels were attenuated by 1.8% saline injection and totally prevented by 3.6% saline administration. These results strongly argue in favor of a primary role of osmoregulation in ethanol-induced taurine release. Ethanol-induced cell swelling probably activates volume-sensitive channels, and taurine passively diffuses outside the cells along its concentration gradient.

Inositol and higher inositol phosphates in neural tissues: homeostasis, metabolism and functional significance

Inositol phospholipids and inositol phosphates mediate well-established functions in signal transduction and in Ca2+ homeostasis in the CNS and non-neural tissues. More recently, there has been renewed interest in other roles that both myo-inositol and its highly phosphorylated forms may play in neural function. We review evidence that myo-inositol serves as a clinically relevant osmolyte in the CNS, and that its hexakisphosphate and pyrophosphorylated derivatives may play roles in such diverse cellular functions as DNA repair, nuclear RNA export and synaptic membrane trafficking.

Brain uptake of myoinositol after exogenous administration

An acute increase in plasma tonicity results in an adaptive increase in brain organic osmolyte content, but this process requires several days to occur. Slow reaccumulation of brain organic osmolytes may contribute to osmotic demyelination. It was investigated whether administration of intravenous myoinositol in rats could speed entry of the osmolyte into the brain. Two groups of animals were studied: normonatremic animals and animals with hyponatremia (105 mmol/L) of 3-d duration. Animals were intravenously administered either 1 M NaCl to induce a 25 to 28 mM increase in serum sodium concentration over 200 min or an infusate that maintained serum sodium concentration. In some animals, myoinositol was administered intravenously over the same time period to raise plasma myoinositol levels by 5 to 10 mM. Brain myoinositol, electrolyte, and water contents were determined at the end of the infusions. In both normonatremic and hyponatremic rats, infusion of hypertonic saline without myoinositol or infusion of myoinositol without hypertonic saline did not increase brain myoinositol levels above control levels. In normonatremic animals, concurrent infusion of hypertonic saline and myoinositol increased brain myoinositol levels by about 50% above control levels. Brain myoinositol content in animals with uncorrected hyponatremia was about 50% of that found in normonatremic controls; concurrent infusion of hypertonic saline and myoinositol increased brain myoinositol to levels similar to those found in normonatremic controls. Intravenous infusion of myoinositol did not alter brain water content compared with animals not infused with myoinositol. In conclusion, systemic infusion of myoinositol can rapidly increase brain myoinositol content, but only when plasma tonicity is concomitantly increased.

Volume supplementation with iso-sodium solution prevents hypernatremia after head injury

OBJECTIVE

To evaluate our developed volume supplement protocol in preventing hypernatremia after head injury.

METHODS

Iso-sodium solution was infused to keep the 8-hour water balance positive in 20 head-injured patients with hypotonic urine.

RESULTS

Serum sodium concentrations moved to within a normal range in 6 patients and were temporarily increased in 12 patients. Seven of the 12 showed a negative cumulative water balance and slightly low creatinine clearance. Mean arterial pressure in the other five patients was lower after supplementation and was positively related to sodium excretion. Hypernatremia could not be prevented in the other two patients and they did not survive. Creatinine clearance was below 40 mL/min/m2 in these two patients before supplementation.

CONCLUSION

Our protocol worked effectively in patients in whom renal function was preserved. Decreased creatinine clearance because of preexisting dehydration and lower arterial pressure disturbed increase in urinary sodium excretion and temporarily aggravated the hypernatremia.

Gene expression of taurine transporter and taurine biosynthetic enzymes in brain of rats with acute or chronic hyperosmotic plasma. A comparative study with gene expression of myo-inositol transporter, betaine transporter and sorbitol biosynthetic enzyme

Cells exposed to hyperosmotic conditions maintain their volume by accumulating organic osmolytes. Taurine is considered as an osmolyte in brain cells. Accumulation of other osmolytes (sorbitol, myo-inositol and betaine), was shown in renal cells to result from an upregulation of the expression of the genes regulating osmolyte cell content. We have investigated the gene expression of the taurine transporter (TauT) and of the taurine biosynthetic enzymes, cysteine dioxygenase (CDO) and cysteine sulfinate decarboxylase (CSD) by measuring their mRNA levels in brain of salt-loaded rats. mRNA levels of genes previously identified as osmosensitive, namely aldose reductase (AR), myo-inositol transporter (SMIT) and betaine transporter (BGT1) were also determined. In whole brain, TauT-, SMIT- and BGT1-mRNA levels were significantly increased following acute salt-loading but SMIT-mRNA levels only remained elevated following chronic salt-loading while CDO-, CSD- and AR-mRNA levels remained unchanged in both conditions. Following acute salt-loading, mRNA levels of TauT, CDO, CSD, SMIT, BGT1 and AR were increased in cerebral cortex while SMIT- and BGT1-mRNA levels only were increased in striatum and habenula.TauT, CDO and CSD genes may be upregulated in brain of salt-loaded rats but the upregulation of the TauT gene appears more widespread. TauT, CDO and CSD are thus putative osmosensitive genes. However the actual pattern (amplitude, time course and regional occurrence) of the upregulation of each of the putative (TauT, CDO and CSD) and established (AR, SMIT and BGT1) osmosensitive genes differs markedly. This indicates that there exist other factors in brain cells which can selectively prevent the upregulation of these genes by hyperosmolarity.

Hypertonic induction of aquaporin-5 expression through an ERK-dependent pathway

Aquaporin-5 (AQP5) is a water channel protein expressed in lung, salivary gland, and lacrimal gland epithelia. Each of these sites may experience fluctuations in surface liquid osmolarity; however, osmotic regulation of AQP5 expression has not been reported. This study demonstrates that AQP5 is induced by hypertonic stress and that induction requires activation of extracellular signal-regulated kinase (ERK). Incubation of mouse lung epithelial cells (MLE-15) in hypertonic medium produced a dose-dependent increase in AQP5 expression; AQP5 protein peaked by 24 h and returned to baseline levels within hours of returning cells to isotonic medium. AQP5 induction was observed only with relatively impermeable solutes, suggesting an osmotic pressure gradient is required for induction. ERK was selectively activated in MLE-15 cells by hypertonic stress, and inhibition of ERK activation with two distinct mitogen-activated extracellular regulated kinase kinase (MEK) inhibitors, U0126 and PD98059, blocked AQP5 induction. AQP5 induction was also observed in the lung, salivary, and lacrimal glands of hyperosmolar rats, suggesting potential physiologic relevance for osmotic regulation of AQP5 expression. This report provides the first example of hypertonic induction of an extrarenal aquaporin, as well as the first association between mitogen-activated protein kinase signaling and aquaporin expression.

Rapid and transient up-regulation of Na+/myo-inositol cotransporter transcription in the brain of acute hypernatremic rats

The osmoregulatory system is well developed in the brain. Osmolytes contribute to maintenance of cell volume and cellular functions without changing intracellular ionic composition. Myo-inositol is regarded as one of the major osmolytes in the brain. In the present study, we investigated the changes in expressions of sodium myo-inositol cotransporter (SMIT) mRNA in the brain of acute hypernatremic rats by in-situ hybridization and Northern blot methods. Under moderate acute hypernatremic conditions, SMIT mRNA level increased markedly at 1 h and returned to almost control levels at 3 h, in accordance with plasma Na+ concentrations. Especially, distinct increases in SMIT mRNA expression were observed in the granule cells and glial cells in the cerebellum. These findings indicate that SMIT plays an important role in osmoregulation, especially in the early stages of acute hypernatremia in the brain.

Role of organic osmolytes in myelinolysis. A topographic study in rats after rapid correction of hyponatremia

Organic osmolytes have been implicated in the pathogenesis of myelinolysis because some of them are accumulated slowly during correction of chronic hyponatremia. I investigated whether there was a topographic correlation between demyelinative lesions and the regional changes of organic osmolytes after rapid correction of chronic hyponatremia. In normal female Sprague-Dawley rats, concentrations of glutamate, glutamine, taurine, and betaine were highest in the cerebral cortex and decreased toward the brain stem. Conversely, glycine level was highest in the brainstem, and decreased toward the cortex. Myoinositol, glycerophosphorylcholine, glycerophosphorylethanolamine, and creatine were distributed more evenly. In chronic hyponatremic rats (plasma Na 110 +/- 4 meq/liter), organic osmolytes decreased globally with the total loss ranging from 13 (medulla) to 24 (cerebellum) mmol/kg H2O. After rapid correction with intraperitoneal injection of hypertonic saline, the recovery of the loss of organic osmolytes was 48% in the cerebral cortex, cerebellum, and medulla oblongata, 44% in pons, but only 17% in midbrain and 36% in striatum. Histopathology of the brain was examined in nine rats 2-7 d after correction of hyponatremia. Large demyelinative lesions were seen persistently in the midbrain and striatum, and smaller lesions in cerebrum, cerebellum, and pons were found less frequently. This is the first report of regional distribution of brain organic osmolytes. After rapid correction of chronic hyponatremia, a topographic correlation between demyelination lesions and delayed accumulation of organic osmolytes exists.

Predictive factors of early postoperative graft function in human liver transplantation

To identify factors predictive of early postoperative graft function, we analyzed 54 variables--including easily available clinical and laboratory data prospectively obtained from organ donors, transplant recipients and surgical procedures in 168 consecutive liver transplantations. Early postoperative graft function was classified into three groups according to a scoring system ranging from 3 to 9 based on peak serum ALT values, mean bile output and lowest prothrombin activity measured during the 72 hr after transplant: group 1 (score 3 to 4, good graft function; n = 73), group 2 (score 5 to 6, moderate dysfunction; n = 50) and group 3 (score, 7 to 9, severe dysfunction; n = 45). In univariate analyses, 8 of the 54 variables analyzed were statistically significant (p < 0.05) predictors of severe graft dysfunction: high serum sodium concentration and brain death caused by cranial trauma in organ donors, advanced age and low prothrombin activity in transplant recipients, prolonged total ischemia time and large transfusions of red blood cells, fresh frozen plasma and platelets during surgery. After introduction of these eight variables in a multivariate analysis, only four were found to independently predict early postoperative graft function: donor serum sodium concentration, total ischemia time, platelet transfusion during surgery and recipient prothrombin activity. In 52 liver transplantations, in which the predictive value of liver tissue adenine nucleotide concentration and several biochemical sensitive markers of donor nutritional status was also analyzed, only the ATP level in liver tissue obtained at the time of organ reperfusion was identified as an independent predictor of initial graft function.(ABSTRACT TRUNCATED AT 250 WORDS)

Osmoregulatory changes in myo-inositol content and Na+/myo-inositol cotransport in rat cortical astrocytes

Exposure of cortical astrocytes to 325, 350, or 390 mosM culture media for 48 h caused a 1.4-, 2.1-, and 3.5-fold increase, respectively, in cellular content of the compatible osmolyte myo-inositol. Elevated myo-inositol levels accounted for approximately 56-100% of the solute needed by the cells for complete volume regulation under hypertonic conditions. Myo-inositol accumulation was associated with 4-5-fold (peak rate) and 1.8-2-fold (steady-state rate) increases in the rate of Na(+)-dependent myo-inositol uptake when cells were acclimated to 390 mosM culture medium for 12 h or 24-96 h, respectively. When medium osmolality was elevated by 25 mosM, peak and steady-state increases in myo-inositol uptake of 1.7-fold and 1.3-fold, respectively, were observed. Exposure to 390 mosM medium for 12-48 h induced a 3-8-fold increase in cotransporter mRNA levels suggesting that the increase in myo-inositol uptake is brought about by increased cotransporter gene expression. Abrupt return of hypertonic cells to an isotonic medium induced a rapid increase in myo-inositol efflux and a return of cotransporter mRNA to control values in < 2 h. In contrast, the cotransporter remained fully activated at hypertonic levels for 16 h. Between 16-24 h after the transfer, the rate of myo-inositol uptake returned to control values. The remarkable sensitivity of the cotransporter to hypertonic stress indicates that upregulation of myo-inositol transport in glial cells is likely to occur in a variety of disease states that cause an elevation of plasma osmolality. Slow downregulation of the cotransporter may be responsible in part for the slow loss of myo-inositol and cerebral edema that occurs with too rapid correction of chronic plasma hypertonicity.

Osmotic regulation of myo-inositol uptake in primary astrocyte cultures

Uptake of myo-inositol by astrocytes in hypertonic medium (440 mosm/kg H2O) was increased near 3-fold after incubation for 24 hours, which continued for 72 hours, as compared with the uptake by cells cultured in isotonic medium (38 nmoles/mg protein). myo-Inositol uptake by astrocytes cultured in hypotonic medium (180 mosm/kg H2O) for periods up to 72 hours was reduced by 74% to 8 to 10 nmoles/mg protein. Astrocytes incubated in either hypotonic or hypertonic medium for 24 hours and then placed in isotonic medium reversed the initial down- or up-regulation of uptake. Activation of chronic RVD and RVI correlates with regulation of myo-inositol uptake. A 30 to 40 mosm/kg H2O deviation from physiological osmolality can influence myo-inositol homeostasis. The intracellular content of myo-inositol in astrocytes in isotonic medium was 25.6 +/- 1.3 micrograms/mg protein (28 mM). This level of myo-inositol is sufficient for this compound to function as an osmoregulator in primary astrocytes and it is likely to contribute to the maintenance of brain volume.

Regulation of mammalian brain cell volume

Maintenance of brain cell volume is of crucial importance for normal central nervous system (CNS) function. This review considers volume regulation primarily in response to disturbances of body fluid osmolality. Brain cells counter the tendency to swell or shrink by appropriate adjustment of their internal osmotic potential. This is achieved by loss or uptake of inorganic ions and low molecular weight organic solutes (osmolytes). The latter comprise mainly amino acids, myoinositol, choline, and methylamines. Taurine may be of particular importance in volume control, especially in young animals. Brain cell volume regulation, however, is only one contributory factor to maintenance of constant brain volume (water content), and operates in parallel with important alterations in bulk fluid and electrolyte movement across the blood-brain barrier and between the interstitium and cerebrospinal fluid, which themselves moderate the requirement for transient alteration in cell volume during acute osmotic imbalance. Although altered cerebral content of inorganic ions and osmolytes are usually regarded as responses, respectively, to acute and chronic osmotic disturbances, osmolytes (especially taurine) may also participate in short-term cell volume regulation.

[Osmolality and brain]

A modification of serum osmolarity induces always movements of water across cell membranes and therefore variations of cell volume of all tissues, including brain. To avoid a severe cell dehydration or hyperhydration, the organism has several regulation means called osmoregulation. Cerebral osmoregulation is essential as the brain is contained in a unexpandable box. In comparison with other organs, this phenomenon is complex and particular as: 1) cerebral volume consists of 3 sub spaces (intracellular, extracellular and cerebrospinal fluid [CSF]); 2) exists a blood-brain barrier (BBB) which behaves functionally as a semi-permeable membrane, essentially sensitive to osmolar disturbances. This brain volume regulation mechanism is working whatever the nature of the solutes initiating the osmotic deviation (sodium, glucose, mannitol...). Cerebral osmoregulation results from intracerebral osmolar modifications. Thus, every variation of plasma osmolarity elicits a similar variation of intracerebral osmolarity. This phenomenon results from modifications of the brain cell "protective" osmoles content. When the osmolar disturbance occurs quickly (in a few hours), cerebral osmoregulation is not complete. It results essentially from modifications of brain cell inorganic solutes content, i.e. electrolytes (Na, K, Cl) which originate from plasma, CSF and extracellular brain spaces uptake. When the osmolar disturbance is more progressive, cerebral osmoregulation is complete. The brain volume returns then to its initial value, by increasing its brain cell electrolytes, but above all organic "idiogenic" osmoles content. These idiogenic osmoles are identified as amino acids, polyols and trimethylamines. During treatment, the delayed normalization of brain osmolarity compared with plasma osmolarity prescribes a slow correction of the osmolar disturbance, as much as it is a chronic one.

Maintenance of cell volume in the central nervous system

Maintenance of the ionic and osmotic composition and volume of intra- and extracellular fluids in the brain is crucial for normal functioning of the central nervous system (CNS). Osmoregulation in the CNS is mediated by solute and water transport across the blood-brain barrier, choroid plexus and plasma membrane of glial cells and neurons. Despite its clinical and physiological significance, however, little is known about the underlying cellular and molecular mechanisms by which CNS osmotic and ionic balance is maintained. In this review, I will discuss our current understanding of cell volume regulation in the CNS and how it relates to various disease processes, such as hyponatremia, renal failure and hypernatremia. A detailed understanding of brain osmoregulatory processes represents a fundamental physiological problem and is required for the treatment of numerous disease states, particularly those encountered in the practice of nephrology.

Rapid correction of hyponatremia produces differential effects on brain osmolyte and electrolyte reaccumulation in rats

Studies from these and other laboratories have shown that hyponatremia causes marked depletion of both electrolytes and organic osmolytes from the brain. The present studies evaluated brain reaccumulation of both classes of solute after correction of chronic hyponatremia. Hyponatremia was induced by subcutaneous infusions of 1-deamino-[8-D-arginine]-vasopressin (dDAVP) in rats fed a balanced liquid diet. After 14 days of sustained hyponatremia the dDAVP minipumps were removed causing rapid correction of plasma sodium concentrations from 104 +/- 1 mmol/l to 139 +/- 1 mmol/l in 24 h. Water and solute contents were measured in brain extracts both before and for 5 days after correction of the hyponatremia, and compared to values in normonatremic rats maintained on the same diet for 14 days. Our results demonstrate that electrolytes, particularly Na+ and Cl-, reaccumulate rapidly in the brain, resulting in a significant overshoot above normal control brain Na+ and Cl- contents as early as 24 h after correction. In contrast, organic osmolyte reaccumulation occurs more slowly, requiring 5 or more days for a return to normal control brain contents in most cases. A prominent exception to this pattern was glutamate, which also returned rapidly to normal brain contents within 24 h similar to the electrolytes. Quantitative analysis of brain water and solute contents after correction of hyponatremia indicated that the reaccumulation of electrolytes and organic osmolytes was sufficient to account for the changes in brain volume that occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain osmoregulation during extreme and moderate dehydration in a rat model of severe DKA

To determine if osmoprotective molecules accumulate in the brain during severe DKA with extreme (DKA-E) and moderate (DKA-M) dehydration, Fischer 344 rats (250-350g) were given STZ 45 mg/kg (i.p.) and allowed food and water ad lib. DKA-M received NaCl 77 mmol/L 60 ml/kg (i.p.) q 4 hrs. on day 2. All rats were anesthetized and sacrificed at 48 hrs. Half of each brain was used to measure water content (BWC) and half to measure Na+, K+, and organic osmoles by HPLC. Just prior to expiration, values for mean concentration of serum glucose (mmol/L) percent weight loss and median blood pH for DKA-E were 33.4, 19%, 6.98; for DKA-M, 16.8, 7.5% and 6.84, respectively. Means +/- SEM were compared by Student's t-test. Percent BWC was 76.3, 77.3 and 77.6 in DKA-E, DKA-M and normal controls, respectively (NS). Brain Na+ and K+ were increased in DKA-M compared to controls (p < .05) but not significantly different in DKA-E compared to controls. Of organic osmoles measured (umol/g wet weight) taurine was significantly increased (p < .01) in DKA-E and DKA-M (8.04 +/- .39 and 9.73 +/- .78, respectively) as compared to controls (5.92 +/- .35) as was myoinositol in DKA-E compared to controls (9.96 +/- .39 vs. 8.87 +/- .28) (p < .05) and urea in DKA-E as compared to controls (14.24 +/- 3.9 vs. 4.14 +/- .52) (p < .01). DKA-M were not significantly different for brain myoinositol or urea as compared to control animals. There was no significant difference in brain glutamine between either study group and controls. Preservation of brain water despite systemic dehydration can be partly explained by increased brain concentrations of osmoprotective molecules. Such adaption in the clinical setting of DKA warrants a cautious repair of dehydration and hyperosmolality.

Extracellular and cerebrospinal fluids

The mechanism of formation of extracellular fluid is first described, followed by an explanation of the relation between osmotic force, reflection coefficient and molecular size. The possible mechanism of brain extracellular fluid formation is then proposed in relation to the restriction offered by the blood-brain barrier. The functions and compositions of cerebrospinal fluid (CSF) are then described followed by sections on the process of formation of CSF, the non-electrolytes and proteins in CSF, the drainage mechanisms and protein synthesis by the choroid plexus.

Hyponatremia causes large sustained reductions in brain content of multiple organic osmolytes in rats

Brain adaptation to hypoosmolality is known to involve volume regulatory losses of both extracellular and intracellular electrolytes. We studied the effects of acute and chronic hypoosmolality on brain content of organic osmolytes as well as electrolytes in rats to ascertain the relative contributions of different brain solutes to the brain volume regulation that occurs under these conditions. Brains were dissected from rats after 2, 7 and 14 d of sustained hyponatremia induced by continuous infusion of 1-deamino-[8-D-arginine]-vasopressin (DDVAP) in combination with a liquid formula, along with control rats fed the same formula in the absence of DDAVP infusions. One half of each brain was analyzed for organic osmolyte contents and the other half for water and electrolyte contents. Brain Na+, K+ and Cl- and multiple organic osmolytes (glutamate, creatine, taurine, myo-inositol, glutamine and glycerophosphoryl-choline) decreased markedly by 2 d of hyponatremia, and brain electrolyte and most organic osmolyte contents then remained at these reduced levels throughout the duration of the hyponatremia. Although the absolute magnitude of the brain electrolyte losses was greater than the magnitude of the brain organic osmolyte losses, the organic osmolyte losses accounted for approximately 35% of the total measured brain solute losses during sustained hyponatremia. These results demonstrate that organic osmolytes constitute a significant proportion of the brain solute losses that take place during hyponatremia, and indicate that reductions in both organic osmolyte and electrolyte contents are necessary to accomplish brain volume regulation during adaptation to sustained hypoosmolality.

Extracellular volume decreases while cell volume is maintained by ion uptake in rat brain during acute hypernatremia

1. Regulation of brain extracellular and intracellular water content, regarded as volume, and electrolytes in response to 90 min of hypernatremia has been studied in the cerebral cortex of rats under urethane anaesthetic. 2. Total tissue electrolytes and water were partitioned between extracellular and intracellular compartments based on measurements made in two series of experiments. In one, tissue samples were collected and analysed for total water, Na+, K+ and Cl-. In the other, tissue extracellular volume fraction, [Na+] and [K+] were measured in situ using ion-selective microelectrodes. 3. Osmotically induced water loss from cerebral cortex was less than that predicted for ideal osmotic behaviour, revealing a degree of volume regulation, and this regulation was associated with net tissue uptake of Na+, Cl- and K+. 4. Total water content was 3.77 g H2O (g dry weight)-1 in control cortex and this decreased by 7% after 30 min of hypernatremia and then remained relatively stable at this value. Control extracellular water content, based on an extracellular volume fraction of 0.18, was 0.88 g H2O (g dry weight)-1. Control intracellular water content, estimated as the difference between total and extracellular water contents, was 2.89 g H2O (g dry weight)-1. After 30 min of hypernatremia, extracellular water content decreased by an average of 27% but intracellular water did not change. This indicates selective regulation of cell volume. By 90 min the extracellular water content had decreased by 47% and the loss in extracellular water content appeared to be accompanied by a roughly equivalent increase in intracellular water content. The intracellular volume increase, however, was not statistically significant. The tortuosity of the extracellular space averaged 1.57 and increased to 1.65 during the hypernatremia. 5. Brain extracellular fluid and plasma [Na+] were roughly equal in control tissue. Both increased by 30 mu equiv (g H2O)-1 as a result of the hypernatremia, although extracellular [Na+] lagged behind the plasma value during much of the first 60 min of hypernatremia. Extracellular [K+] was homeostatically regulated at 3 mu equiv (g H2O)-1 independent of changes in plasma electrolytes. 6. Estimates of extracellular and intracellular ion content (mu equiv (g dry weight)-1) indicate that extracellular Na+, Cl- and K+ content decreased during hypernatremia, by 32, 21 and 42% respectively, whereas intracellular ion content increased by 100, 169 and 5% respectively. 7. It is concluded that during acute hypernatremia the extracellular space decreases in volume through the loss of water and electrolytes while the intracellular compartment maintains its water content and gains electrolytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Selected aspects of cell volume control in renal cortical and medullary tissue

Under normal physiological conditions, demands placed on mammalian renal cortical cells are quite different from those in the medulla. Cortical proximal tubule cells exist in an isotonic environment, but must resorb vast amounts of filtered fluid and solute, and also adjust to solute generated from cellular metabolism. In addition, cortical cells must also adjust to occasional pathological derangements in blood osmolality. By contrast, human medullary cells have a smaller solute resorptive load, but exist in a milieu where osmolality varies from 40 to more than 1200 mosmol/kg H2O, depending on water intake. Remarkably, the cells maintain a near normal size despite these stresses. Under isosmotic conditions, the primary regulator of cell volume is Na-K ATPase. In its absence, factors such as external protein, extracellular matrix and basement membrane, cytoskeleton, and perhaps formation of cytoplasmic vesicular-like structures help prevent cells from swelling massively. Under anisosmotic conditions, a variety of transport processes operating across basolateral and apical membranes either remove solute from or add solute (and water) to cells to minimize changes in their size. Medullary cells have the additional ability to accumulate organic, non-toxic, osmolytes that offset external hypertonicity and allow cells to maintain normal size without increasing cellular inorganic ion concentrations.

Study of brain electrolytes and organic osmolytes during correction of chronic hyponatremia. Implications for the pathogenesis of central pontine myelinolysis

Osmotic injury induced by rapid correction of severe chronic hyponatremia has been implicated in the development of central pontine myelinolysis. Organic osmolytes known previously as "idiogenic osmoles" accumulate intracellularly to protect cells from osmotic injury. We investigated the changes of these organic osmolytes as well as electrolytes in the brain during the induction and correction of chronic hyponatremia. Using 1H-nuclear magnetic resonance spectroscopy and HPLC, we found that in rats with chronic hyponatremia (3 d, serum sodium = 109 +/- 3 meq/liter), brain concentrations of myoinositol (41%), glycerophosphorylcholine (45%), phosphocreatine/creatine (60%), glutamate (53%), glutamine (45%), and taurine (37%) were all significantly decreased compared with control values (percentage control value shown, all P less than 0.01). The contribution of measured organic osmolytes and electrolytes to the total brain osmolality change was 23 and 72%, respectively. With rapid correction by 5% NaCl infusion, significant brain dehydration and elevation of brain Na and Cl levels above the normal range occurred at 24 h. These changes were not seen with slow correction by water deprivation. Reaccumulation of most organic osmolytes except glycerophosphorylcholine is delayed during the correction of hyponatremia and is independent of the correction rate of serum sodium. It is concluded that: most of the change of brain osmolality in chronic hyponatremia can be accounted by the changes in organic osmolytes and brain electrolytes; and rapid correction of hyponatremia is associated with an overshoot of brain sodium and chloride levels along with a low organic osmolyte level. The high cerebral ion concentrations in the absence of adequate concentrations of organic osmolytes may be relevant to the development of central pontine myelinolysis.

Upregulation of inositol transport mediates inositol accumulation in hyperosmolar brain cells

Attempts to understand brain volume regulation have been greatly hampered by the structural complexity of the mammalian central nervous system, indicating a need for the investigation of cultured brain cell lines whose behavior reflects that observed in situ. We demonstrate here that rat C6 glioma cells exhibit a pattern of hyperosmolar volume regulation qualitatively similar to that of the intact brain. Chronic (2-6 days) acclimation of C6 cells to high NaCl media (440 or 590 mosM) resulted in a 46-133 mM increase in cellular inositol, a known major brain osmolyte. C6 cells exposed acutely to 440 mosM medium shrank abruptly and then underwent a complete regulatory volume increase (RVI) within 4 h. Inositol levels began to increase after 10 h of hyperosmolar stress and reached maximal values by 24 h, suggesting that RVI is initially mediated by inorganic ion uptake. [3H]inositol uptake measurements revealed a sevenfold stimulation of phlorizin-inhibitable inositol transport in hyperosmotic cells. The enhancement of inositol transport paralleled the rise in cellular inositol content. Phlorizin reduced inositol accumulation in hyperosmolar cells by 44%. Our studies provide the first demonstration of RVI and organic osmolyte accumulation in a cultured brain cell line.

Amino acids as volume-regulatory osmolytes in mammalian cells

1. This review summarizes current knowledge relating to the volume-regulatory and osmoprotective functions of amino acids in mammalian cells exposed to anisosmotic fluids. 2. Experiments in vivo and in vitro have established that they play a significant role in regulating brain cell volume under these conditions, and that taurine may be of particular importance in this respect. 3. Their possible role in renal medulla is discussed, and it is suggested that they may protect cells against acute (but not long-term) osmotic variation. 4. Evidence is briefly presented regarding adaptive changes in amino acid content of other cell types.

The role of polyols in cerebral cell volume regulation in hypernatremic and hyponatremic states

To clarify the role of the sugar polyols, sorbitol and myo-inositol, in cerebral cell volume regulation, we studied the effect of sorbinil, an inhibitor of aldose and aldehyde reductase, on the size of the cerebral water compartments in rats with hypernatremia, hyponatremia and normonatremia. Experimental animals were pretreated with sorbinil, while comparison rats received the drug vehicle. Rats were made hypernatremic for 96 h by water deprivation and injections of hypertonic saline, while hyponatremia was provoked over 48 h by daily administration of 5% dextrose in water and vasopressin. Sorbinil treatment was continued throughout the hyper- and hyponatremic periods. The severity of hypernatremia and hyponatremia was similar in sorbinil-treated and corresponding vehicle-treated rats. Brain electrolyte content and the size of the cerebral intracellular water compartment were comparable in sorbinil-treated rats vs. controls under hypernatremic and hyponatremic conditions. Sorbinil reduced the cerebral sorbitol content by approximately 50%, irrespective of the serum Na+ concentration. In contrast, sorbinil had no effect on brain myo-inositol content which rose by 114% during chronic hypernatremia (P less than 0.0001). Cerebral levels of myo-inositol did not decline in hyponatremic rats. We conclude that (1) sorbitol is not an essential cerebral osmolyte; and (2) myo-inositol is involved in the maintenance of brain cell volume during severe hypernatremia but not under hyponatremic conditions.

Hyperosmolar states

The composition of the extracellular fluid (ECF) must remain stable for cells to function properly. In normal individuals vasopressin and thirst zealously maintain the total ECF concentration, or osmolality, within a narrow range. Disruption of these regulatory mechanisms or rapid addition of solute to the ECF can lead to hyperosmolality. The serious neurologic symptoms that accompany many forms of hyperosmolality can be explained by understanding the physiologic response of cells to the osmotic stress. This review describes the physiology, pathophysiology, differential diagnosis, and therapy of hyperosmolar states.

Manipulation of plasma membrane fatty acid composition of fetal rat brain cells grown in a serum-free defined medium

Modifications of plasma membrane acyl-linked phospholipid fatty acid composition were produced by supplementing the culture medium with essential fatty acids. The plasma membrane fraction was purified by Percoll gradient centrifugation from dissociated fetal rat brain cells grown in a serum-free culture medium. Both the concentration dependence and the time course of the modifications were examined. Supplementation of the medium with essential polyunsaturated fatty acid, linolenic acid (18:3 omega 3) or linoleic acid (18:2 omega 6), produced incorporation of the elongated and desaturated products of omega 3 or omega 6 class, respectively, i.e., the incorporation was class specific. Within each class, the most unsaturated and elongated members, i.e., terminal members, were preferentially incorporated until they reached a maximum concentration within 6-7 days. At higher concentrations of supplemented fatty acids, additional class specific incorporation in plasma membrane was produced by an increase in the concentration of intermediate members. At the same time, the concentration of monounsaturated fatty acids declined and that of saturated fatty acids remained unchanged. The modifications in fatty acid composition were reversible, with the time course similar to that of incorporation. The total plasma membrane phospholipid and sterol contents did not change with alterations of fatty acid composition, but did change with time in culture. This preparation should prove useful for investigating the role of polyunsaturated fatty acids in brain cell functions, including neuronal excitability.