[Energetic disturbance of cation transport as a cause of intracellular brain edema]

The normal and pathological physiology of brain water

The physicochemical properties of water enable it to act as a solvent for electrolytes, and to influence the molecular configuration and hence the function--enzymatic in particular--of polypeptide chains in biological systems. The association of water with electrolytes determines the osmotic regulation of cell volume and allows the establishment of the transmembrane ion concentration gradients that underlie nerve excitation and impulse conduction. Fluid in the central nervous system is distributed in the intracellular and extracellular spaces (ICS, ECS) of the brain parenchyma, the cerebrospinal fluid, and the vascular compartment--the brain capillaries and small arteries and veins. Regulated exchange of fluid between these various compartments occurs at the blood-brain barrier (BBB), and at the ventricular ependyma and choroid plexus, and, on the brain surface, at the pia mater. The normal BBB is relatively permeable to water, but considerably less so to ions, including the principal electrolytes Brain fluid regulation takes place within the context of systemic fluid volume control, which depends on the mutual interaction of osmo-, volume-, and pressure-receptors in the hypothalamus, heart and kidney, hormones such as vasopressin, renin-angiotensin, aldosterone, atriopeptins, and digitalis-like immunoreactive substance, and their respective sites of action. Evidence for specific transport capabilities of the cerebral capillary endothelium, for example high Na+K(+)-ATPase activity and the presence at the abluminal surface of a Na(+)--H+ antiporter, suggests that cerebral microvessels play a more active part in brain volume regulation and ion homoeostasis than do capillaries in other vascular beds. The normal brain ECS amounts to 12-19% of brain volume, and is markedly reduced in anoxia, ischaemia, metabolic poisoning, spreading depression, and conventional procedures for histological fixation. The asymmetrical distributions of Na+ K+ and Ca2+ between ICS and ECS underlie the roles of these cations in nerve excitation and conduction, and in signal transduction. The relatively large volume of the CSF, and extensive diffusional exchange of many substances between brain ECS and CSF, augment the ion-homeostasing capacity of the ECS. The choroid plexus, in addition to secreting CSF principally by biochemical mechanisms (there is an additional small component from the extracellular fluid), actively transports some substances from the blood (e.g. nucleotides and ascorbic acid), and actively removes others from the CSF. In contrast with CSF secretion, CSF reabsorption is principally a biomechanical process, passively dependent on the CSF-dural sinus pressure gradient. Pathological increases in intracranial water content imply development of an intracranial mass lesion. The additional water may be distributed diffusely within the brain parenchyma as brain oedema, as a cyst, or as increase in ventricular volume due to hydrocephalus. Brain oedema is classified on the basis of pathophysiology into four categories, vasogenic, cytotoxic, osmotic and hydrostatic. The clinical conditions in which brain oedema presents the greatest problems are tumour, ischaemia, and head injury. Peritumoural oedema is predominantly vasogenic and related to BBB dysfunction. Ischaemic oedema is initially cytotoxic, with a shift of Na+ and CI- ions from ECS to ICS, followed by osmotically obliged water, this shift can be detected by diffusion-weighted MRI. Later in the evolution of an ischaemic lesion the oedema becomes vasogenic, with disruption of the BBB. Recent imaging studies in patients with head injury suggest that the development of traumatic brain oedema may follow a biphasic time course similar to that of ischaemic oedema. Hydrocephalus is associated in the great majority of cases with an obstruction to the circulation or drainage of CSF, or, occasionally, with overproduction of CSF by a choroid plexus papilloma. In either case, the consequence is a ris

The response of focal ischemic cerebral edema to dexamethasone

Twenty-four h after permanent occlusion of the middle cerebral artery (MCA) in the cat, the hemispheric swelling due to edema is markedly reduced under treatment with large doses of dexamethasone than is the case with the untreated group. The increase of regional water and sodium content in the MCA territory is less in the dexamethasone treated group, whereas the potassium changes in the ischemic tissue showed only small differences between the two groups. The potassium content of the non-ischemic tissue is slightly increased in the dexamethasone treated animals when comparing with the untreated group. RISA activity in the tissue is increased in the grey and the white matter of both groups. The less marked RISA-131 activity in the cortical grey matter of the treated animals indicates blood-brain barrier damage of a smaller degree due to dexamethasone. These findings indicate a beneficial effect of dexamethasone on local ischemic edema. Regarding our results and the pharmacokinetics of this steroid the dexamethasone loading of a patient has to be in the range of about 100 mg per day for the adult, and has to be started immediately after the onset of a stroke.

The effect of arterial hypertension of focal ischemic edema. An experimental study

The middle cerebral artery (MCA) of cats was occluded permanently for 24h to study the influence of arterial hypertension during the early phase of focal ischemia upon the development of endema and changes of the blood-brain barrier (BBB). In normotensive animals MCA occlusion results in a hemispheric weight increase of about 8% and marked water and electrolyte alterations in both the grey and white matter of the MCA territory. The RISA space increases mainly in the grey matter. Hypertension aggravates these changes significantly, whereby water and electrolyte changes in the grey matter are predominantly concerned, while there is a preferential increase of the RISA space in the white matter. It is suggested that arterial hypertension aggravates the ischemic edema and enhances a vasogenic type of edema in the white matter.

Brain energy metabolism in global brain oedema

Different degrees of severity in global brain oedema were induced by varying amounts of water intoxication (50, 100, 150, and 200 ml Aqua dest./kg b.wt. intravenously) in groups of six cats, which were functionally nephrectomized. Animals loaded with physiological saline and sham-operated served as controls. Two hours following the water load, the tissue concentrations of CrP, ATP, ADP, AMP, pyruvate, glucose, and lactate were determined by optical enzymatic analysis. The results show disturbances in brain energy metabolism dependent on the severity of the brain oedema. The high energy compounds and in consequence the ATP/ADP-ratio, and respectively the energy charge potential, fall in direct relationship to the severity of the brain oedema. Lactate and lactate-pyruvate ratio increase. The energy source of the cell, glucose as well as pyruvate, significantly falls in the group with severe brain oedema. The results of the brain energy metabolism were compared with our previous study concerning the brain water content, rCBF and CPP in global brain oedema (Meinig et al. 1973). The results show that the disturbances of energy metabolism are directly related to the rCBF and are not dependent on CPP over a wide range.

Clearance of edema fluid into cerebrospinal fluid. A mechanism for resolution of vasogenic brain edema

The authors present the results of an investigation studying the resolution of vasogenic brain edema using cold injury in cats. The appearance of RISA-I131 and sucrose-C14 lebeled edema fluid in the ventricular cerebrospinal fluid (CSF) was assessed by means of ventriculocisternal perfusion. The effect of low- or high-pressure perfusion on edema spread was determined by measuring the water, sodium, RISA-I131, and sucrose-C14 content of serial tissue blocks taken from the injured cortex through the white matter to the ventricular ependyma. The findings indicate that increasing the hydrostatic pressure gradient between edematous brain and CSF enhances the clearance of edema fluid into the ventricular CSF. This was conclusively demonstrated with low-pressure ventricular perfusion which markedly diminished the amount of edema close to the ventricles compared to the controls. The concentration of albumin, sodium, and potassium to the fluid removed from the tissue during low-pressure perfusion indicates that bulk flow was the primary method of edema movement through the extracellular space. With high-pressure perfusion the concentration profiles suggested alternative mechanisms of edema resolution, such as diffusion and reabsorption into capillaries.

Cation activities in reversible ischemia of the cat brain

In normothermic anesthetized cats cerebral blood flow was interrupted completely for one hour by arterial clamping and induced hypotension. The effect of ischemia on the ionic gradients of the cerebral cortex was assayed by determining total cortical electrolytes and by recording the activities of extracellular potassium ([K+i1e) and subarachnoid sodium ions ([Na+])s) with ion-sensitive electrodes. During ischemia [K+]e increased from 3.3+/-0.3 to 56+/-5.4 mEq per liter (means+/-SE) and [Na+]s decreased from 133+/-3.8 to 53+/-5.8 mEq per liter. When the brains were recirculated with blood after one hour's ischemia, [K+]e and [Na+]a gradually returned to normal within 45 minutes. The calculated intracellular uptake of sodium during ischemia amounted to 139 mEq per kilogram dry weight, whereas the intracellular release of potassium was only 64 mEq per kilogram. The increase in intracellular cation was accompanied by a movement of water from the extracellular into the intracellular compartment, causing a reversible shrinkage of the extracellular space from 18.9 to 8.5 vol %. The changes in ionic gradients were related to the development and resolution of ischemic brain swelling, and to the elctrophysiological events during and after ischemia.

Role of pressure gradients and bulk flow in dynamics of vasogenic brain edema

The authors present the results of an investigation of the vasogenic type of brain edema using cold injury in cats as a model. Their findings indicate that bulk flow and not diffusion should be considered the main mechanism for the spread of edema through the white matter. This conclusion is based on: 1) comparison of the distances actually traveled by various substances during edema spread with those calculated theoretically for migration of the substances by diffusion; 2) coincidence in the speed of movement by two substances (sucrose and albumin) with widely different diffusion coefficients; 3) measurement of interstitial fluid pressure (IFP) at various distances from the lesion showing the presence of increased IFP in the lesion area and decreasing pressures along the edema pathway toward the normal tissue; and 4) the fact that spreading of edema can be significantly impeded by inducing before the cold lesion an intracellular type of brain edema that reduces the size of the extracellular space (ECS) and increases the resistance to flow of edema fluid. The pressure-volume curve of the brain ECS, as derived from determinations of IFP and tissue water content, indicates that initial steep slope in IFP probably represents the high resistance to fluid mobility through the small diameter extracellular channels and the counteracting resistance of the intermingled structures of brain parenchyma to be separated. Once the IFP exceeds these opposing forces, the ECS dilates, fluid mobility increases, and the edema front advances.

The dependence of the blood to brain passage of radioactive sodium on blood pressure and temperature

Brain sodium uptake (BSU) was calculated from estimated radioactivities of brain and blood, collected from rats which were given [24Na]sodium chloride 30 min and [22Na]sodium chloride 1 min before killing. The calculated BSU values, when plotted against the average blood pressure of the animal during the survival time of 30 min, showed a linear dependence of BSU on blood pressure. In another series of animals, in which in addition to variation of the blood pressure as in the former series, the brain was cooled to 15 degrees C, the resulting regression line showed the same slope, but a significantly lower intercept than at normal temperature. The results indicate the existence of a blood pressure-dependent component of sodium passage, reflecting the exchange of fluid at the blood-brain interface as governed by the Starling hypothesis, and an additional component which being temperature dependent, presumably constitutes an active transport mechanism.

Resuscitation of the monkey brain after one hour's complete ischemia. II. Brain water and electrolytes

Adult normothermic rhesus monkeys were submitted to one hour's complete cerebral ischemia, followed by periods of blood recirculation varying from 45 min to 24 h. The functional impact of ischemia and the subsequent recovery was monitored by electrophysiological recording and a distinction was made between animals with signs of functional recovery and animals without recovery. Prior to ischemia the water content of the gray matter was 81.1 plus or minus 0.3% (mean plus or minus S.D.) and of the white matter 68.9 plus or minus 0.8%. The sodium-potassium ratio in the gray matter was 0.43 plus or minus 0.02 and in the white matter 0.62 plus or minus 0.06. During one hour's ischemia brain water did not change significantly, but the differences in the sodium-potassium ratio in white and gray matter were reduced. Blood recirculation of the brain after ischemia caused a considerable increase in brain water content and a shift in the sodium-potassium ratio up to 1.0. Calculated brain swelling was maximal after 45 min when it reached 11.1% of the total brain volume in an animal with recovery and 12.2% in another one without recovery. In animals with signs of functional recovery brain swelling rapidly diminished, followed by a more gradual normalization of brain electrolytes within 24 h. In animals without functional recovery electrolyte shifts were irreversible or even progressed further. It is concluded that brain swelling and electrolyte derangements following one hour's cerebral ischemia are fully reversible when signs of functional recovery appear and brain metabolism returns.

Energy state and glycolysis in human cerebral edema

✓ A new freeze-stop device using a liquid nitrogen reservoir and an automatic biopsy mechanism has been developed, suitable for rapid, sterile, and standardized sampling of cerebral tissue in man. In animal experiments a 200 mg piece of cerebral cortex was cooled from a room temperature of 18°C to −40°C within 7 sec which is twice as fast as when it was immersed in liquid N2. The method was then applied to metabolic tissue studies of perifocal edematous cortex from patients undergoing neurosurgery for intracranial tumors. Energy-rich phosphate compounds or parameters of the energy state were found to be less affected in this type of brain edema than the glycolytic activity which was markedly enhanced, indicated by lactic and pyruvic acid determinations. The tissue water content correlated closely with the lactic acid concentration, and very little with measurements of the energy state such as the energy charge potential or the adenosinetriphosphate-adenosinediphosphate (ATP/ADP) ratio. It is suggested that in perifocal brain edema increased levels of lactic acid are associated with mechanisms leading to an increased water uptake.

The relation of sodium and potassium ion transport to the respiration and adenine nucleotide content of liver slices treated with inhibitors of respiration

1. The dependence of the net transport of Na(+) and K(+) by rat liver on the respiration has been determined by incubating slices in the presence of varying concentrations of respiratory inhibitors. 2. Neither the rate of net transport nor the total amount of each ion transported was inhibited unless the rate of endogenous respiration was decreased below a critical value of about 330mmol of O(2)/h per kg of protein (i.e. 50% of the total endogenous respiration). 3. The uninhibited rate of respiration could be varied over a twofold range (380-770mmol of O(2)/h per kg of protein) by the use of different substrates, but the critical value for the onset of transport inhibition was quite constant (290-360mmol/h per kg of protein) under these different conditions. 4. Slices incubated at 38 degrees C without inhibitors showed an increase of their ATP content and the concentration ratio ATP/ADP. The final ATP content and concentration ratio, ATP/ADP, of slices treated with different concentrations of inhibitors were closely related to the rate of respiration. 5. The increased ATP content of the control slices during incubation was equal to the increase of total adenine nucleotides. At increasing degrees of respiratory inhibition the relative contributions of ADP and AMP to the total adenine nucleotide content increased. 6. The critical rate of respiration for the onset of inhibition of ion transport and the corresponding contents of adenine nucleotides provide estimates of the maximal values of certain parameters of energy metabolism required for the support of alkali-cation transport in the liver slices.