Cerebrovascular effects of the bradykinin analog RMP-7 in normal and irradiated dog brain

The effects of an intravenous (i.v.) injection of the bradykinin analog RMP-7 (100 ng/kg) were assessed in normal dogs and dogs with focal, radiation-induced brain lesions. A dose of 20 Gy was delivered to a point 0.75 cm from a removable interstitial 125I source; parameters relating to blood flow and permeability were quantified using computed tomography 2-8 weeks after irradiation. Blood flow-related endpoints included regional cerebral blood flow (rCBF), mean transit time of blood and vascular volume, while endpoints related to permeability included blood-to-brain transfer constant (Ki), brain-to-blood transfer constant and plasma volume. In unirradiated brain, an i.v. bolus of RMP-7 administered through the left cephalic vein induced a rapid and transient hypotension and a statistically significant increase in vascular volume; no alterations in any parameter related to permeability were observed. After irradiation, changes in rCBF after RMP-7 depended upon time after exposure, effects presumably due to changing morphology in the irradiated tissues. In the radiation lesions, significant increases in Ki were observed 5 minutes after injection of RMP-7, but those increases were not related to time after irradiation or alteration in blood flow-related parameters. Our results showed that RMP-7 selectively increased permeability in already damaged vasculature without affecting the extent or volume of radiation-induced vasogenic edema. These data suggest that RMP-7 may provide an effective means to enhance the delivery of compounds to an already compromised brain while not exacerbating the potential adverse effects of pre-existing vasogenic edema.     

Colloid determination of fibrin network permeability

The effects of polymers, dextran and polyvinylpyrolidone (PVP) and of albumin on the permeability of thrombin-induced fibrin networks developed in plasma were examined. Both PVP and dextran increased the network permeability and turbidity and increased the fibrin fibre thickness. The effect was molecular weight dependent. Derivation of the dimensionless permeability (permeability/fibre radius2) indicated that the increase in network permeability was mainly from altered arrangement of fibres and not from increased fibre thickness. The effects of albumin on network structure were similar to those of the polymers. Scanning electron microscopy of networks developed in plasma under the influence of dextran and poloxamer 188 showed fibres with increased thickness and a coarse nodular appearance. There was an increased tendency for fibres to be aggregated into clumps. It is suggested that during polymerization fibrin fibres and fibrin polymerization intermediaries behave as colloidal particles. Attractive forces between the particles are generated by soluble macromolecules such as plasma proteins or polymers. Attractive forces increase the thickness of fibrin fibres and induce a more permeable arrangement of the fibres in the network. The most likely colloidal mechanism is depletion flocculation. This would account for (1) the molecular weight dependence and concentration dependence of the effects of macromolecules, (2) the effects of macromolecules which do not bind to fibrin, (3) the effects of the surfactant poloxamer 188. Depletion flocculation may be a significant mechanism for biological regulation of fibrin network permeability by non-specific macromolecules such as soluble proteins or fibrin intermediaries.     

The development of Cop 1 (Copaxone), an innovative drug for the treatment of multiple sclerosis: personal reflections

The aim of the review is to summarize the present knowledge on determinants of transfer of low density lipoprotein (LDL) into the arterial wall, particularly in relation to the risk of development of atherosclerosis. The flux of LDL into the arterial wall (in moles of LDL per surface area per unit of time) has two major determinants, i.e. the LDL concentration in plasma and the arterial wall permeability. LDL enters the arterial wall as intact particles by vesicular ferrying through endothelial cells and/or by passive sieving through pores in or between endothelial cells. Estimates in vivo of the LDL permeability of a normal arterial wall vary between 5 and 100 nl/cm2/h. In laboratory animals, the regional variation in the arterial wall permeability predicts the pattern of subsequent dietary induced atherosclerosis. Moreover, mechanical or immunological injury of the arterial wall increases the LDL permeability and is accompanied by accelerated development of experimental atherosclerosis. This supports the idea that an increased permeability to LDL, like an increased plasma LDL concentration, increases the risk of atherosclerosis. Hypertension, smoking, genetic predisposition, atherosclerosis, and a small size of LDL may all increase the arterial wall permeability to LDL and in this way increase the risk of accelerated development of atherosclerosis. The hypothesis that atherosclerosis risk can be reduced by improving the barrier function of the arterial wall towards the entry of LDL remains to be investigated; agents which directly modulate the LDL permeability of the arterial wall in vivo await identification.     

Thrombin-induced increase in endothelial permeability is associated with changes in cell-to-cell junction organization

Thrombin increases endothelial permeability in a rapid and reversible way. This effect requires the catalytic activity of the enzyme and thrombin receptor engagement. Endothelial cell permeability is mostly regulated by intercellular junction organization. In the present study, we investigated whether opening of intercellular gaps after thrombin treatment could be related to changes in adherence-junction molecular organization. By immunofluorescence analysis, we found that thrombin stimulation of endothelial cells caused a marked alteration of the distribution of vascular endothelial (VE)-cadherin and of the associated catenins. These molecules, which are strictly localized at intercellular boundaries in confluent resting cells, were absent in the areas of intercellular retraction. Immunoprecipitation analysis indicated that thrombin disrupted the VE-cadherin/catenin complex. This effect was reversible and correlated with the increase in endothelial permeability. The use of a protein kinase C inhibitor (calphostin C) blocked both thrombin-induced permeability and disassembly of adherence-junction components. We propose that thrombin's effect on endothelial cell junction organization is an important determinant in the increase in endothelial permeability induced by this agent.     

Colony stimulating factor-1 in human follicular fluid

Blood-brain barrier disruption is common in many neurological diseases. Matrix metalloproteinases are induced in brain injury and increase capillary permeability by attacking the extracellular matrix around cerebral capillaries. Other neutral proteases are also increased in sites of secondary injury, and may contribute to the proteolysis of the blood-brain barrier. Therefore, we studied capillary permeability and histological tissue damage after intracerebral injection of neutrophil elastase, cathepsin G, heparatinase and plasmin. Adult rats were injected intracerebrally with an enzyme. After 1, 4 or 24 h, measurements were made of brain uptake of a radiolabeled tracer, [14C]sucrose. Enzymes that significantly increased capillary permeability were injected into other rats for histological assessment of tissue damage. Elastase increased capillary permeability significantly when compared with controls; maximal damage was seen at 4 h. Plasmin produced smaller increases in permeability at 4 h, exerting its maximal effect on sucrose uptake at 24 h. Cathepsin G had a small effect at 4 h. Heparitinase had no effect. Histologic examination of elastase-injected brains at 24 h revealed multifocal perivascular and intraparenchymal acute hemorrhages accompanied by a polymorphonuclear cell infiltrate. Elastase-injected brains were microscopically similar to saline-injected brains at 1 and 4 h. Plasmin produced fibrinoid changes in the blood vessels at 24 h, coinciding with the maximal increase in capillary permeability. We conclude that neutrophil elastase attacks the capillary extracellular matrix, causing extensive hemorrhage, while plasmin leads to increased vascular permeability and fibrinoid necrosis of blood vessel walls. Differential effects of neutral proteases released secondary to injury could be important in both the acute changes in blood vessel permeability and long-term alterations in vessel structure.     

A study of the ethical duty of physicians to disclose errors

A quantitative immunocytochemical procedure was used for evaluation of the blood-brain barrier (BBB) to endogenous albumin in plaque-forming (PF) and non-plaque-forming (NPF) groups of scrapie-infected mice at the clinical stage of disease. Ultrathin sections of brain samples (cerebral cortex, hippocampus and cerebellum) embedded in resin (Lowicryl K4M) were exposed to anti-mouse albumin antiserum followed by protein A-gold. Using morphometry, the density of immunosignals (gold particles per microns2) was recorded over four compartments: vascular lumen, endothelium, subendothelial space, and brain parenchyma (neuropil). Morphometric and statistical analyses did not reveal significant differences in the barrier function of the microvasculature of the cerebral cortex and hippocampus in either group of mice, although a slight increase in the number of leaking vessels in the PF group was noted. In contrast, in the cerebellum, the permeability of the microvessels to albumin was significantly higher in the PF than in the NPF mouse group, and this was paralleled by the infiltration of the walls of numerous vascular profiles with amyloid deposits (amyloid angiopathy). These data also indicate the existence of distinct regional differences in BBB function in the brain of scrapie-infected mice. The vascular amyloid deposits and the amyloid plaques present in the cerebral cortex of PF mice were labeled with numerous immunosignals suggesting the affinity of extravasated albumin to these deposits. In conclusion, no convincing evidence was obtained indicating that impairment of the BBB, manifested by increased permeability of vascular segments, is directly related to the deposition of amyloid in the vascular wall and in plaques. Segmental impairment of the barrier function seems to be rather the result of disturbed structural integrity of the components of the vascular wall.     

Blood-brain barrier transport of amino acids in healthy controls and in patients with phenylketonuria

Blood-brain barrier permeability to phenylalanine and leucine in four patients with phenylketonuria and in four volunteers was measured five times by the double-indicator method at increasing plasma concentrations of phenylalanine. Based on the permeability-surface area product (PS) from blood to brain (PS1) and on plasma phenylalanine levels, Vmax and the apparent Km for phenylalanine were determined. Statistically significant relationships between plasma phenylalanine and PS1 were established in three out of four volunteers, the average Vmax value being 46.7 nmol/g per min and the apparent Km 0.328 mmol/L. Owing to saturation of the carrier, such a relationship could not be established in the patients. In phenylketonuria, PS1 for phenylalanine and leucine decreased significantly by 55% and 46%, respectively. Transport from brain back to blood, PS2, decreased significantly and cerebral large neutral amino acid net uptake was generally decreased in patients with phenylketonuria. In conclusion, the transport of L-phenylalanine across the human blood-brain barrier follows Michaelis-Menten kinetics. In phenylketonuria, brain permeability to large neutral amino acids is reduced by about 50% and net uptake appears decreased.     

Penetration of fluorescent homologous serum proteins into the wall of the aorta in rats with acute angiotensin hypertension

A few hours of acute angiotensin hypertension in rats increased the permeability of the thoracic part of the aorta for plasma components. The permeability, which was demonstrated by means of homologous circulating fluorescent serum proteins, seemed to be diffuse rather than focal. The fluorescent proteins penetrated into the whole thickness of the aortic wall, but were to a great extent deposited in the subendothelial space and the most luminal part of the tunica media. The deposition took place in the greater part of the circumference of the aortic wall. These results are in agreement with the insudative theory of atherogenesis, and the initial stage seems to be a "damming back" of some of the serum or plasma proteins for deposition in the subendothelial space and the most luminal part of the tunica media.     

Neurogenic disorders of heart and lung function in acute cerebral lesions

Incidence and clinical significance of cardiopulmonary complications of acute cerebral lesions are still unclear. Neurogenic pulmonary edema (NPE) is characterized as an acute, protein-rich lung edema occurring shortly after cerebral lesions associated with an acute rise of intracranial pressure. NPE is infrequently diagnosed, usually in association with head trauma. Pathophysiological mechanisms include a rise of the pulmonary vascular hydrostatic pressure either due to sympathetic innervation with pulmonary vasoconstriction or increased left-atrial pressure following systemic arterial hypertension or an increase in pulmonary capillary permeability. In contrast to NPE, cardiac complications are frequently observed, most consistently in patients with subarachnoid hemorrhage. Typical ECG changes are repolarization abnormalities, similar to those observed in coronary heart disease, and cardiac arrhythmias. The CK-MB may be slightly elevated; echocardiographic findings show a depressed left-ventricular function. Pathological examination reveals myofibrillar necrosis. Cardiac complications are explained with overactivity of the sympathetic innervation and high levels of circulating catecholamines. For adequate treatment, close cardiac monitoring is required in all patients with acute cerebral lesions.     

Two proto-oncogenes that play dual roles in embryonal cell growth and differentiation

BACKGROUND AND PURPOSE: Clinical and experimental data indicate that hyperglycemia can aggravate the consequences of stroke and cerebral ischemia. The purpose of this study was to examine the effects of moderate hyperglycemia on the response of the blood-brain barrier to normothermic (37 degrees C) and hypothermic (30 degrees C) global forebrain ischemia. METHODS: Sixteen rats underwent 20 minutes of four-vessel occlusion followed by 30 minutes of postischemic recirculation. We used the protein tracer horseradish peroxidase as an indicator of increased vascular permeability, and rats were perfusion-fixed for microscopic analysis. To produce moderate hyperglycemia, we gave an intraperitoneal injection of 50% dextrose 15 minutes before the ischemic insult. RESULTS: After normothermic brain ischemia, normoglycemic rats (plasma glucose level, 115 +/- 3 mg/dl) demonstrated extravasated horseradish peroxidase mainly restricted to the cerebral cortex. In contrast, more severe and widespread protein extravasation was documented throughout the neuraxis of hyperglycemic (plasma glucose level, 342 +/- 27) rats. Sites of protein leakage included the cerebral cortex, striatum, hippocampus, thalamus, and cerebellum. Foci of protein extravasation were associated with pial and large penetrating vessels. Intraischemic hypothermia significantly attenuated the blood-brain barrier consequences of hyperglycemic brain ischemia. CONCLUSIONS: Under normothermic ischemic conditions, hyperglycemia significantly worsens the degree of acute blood-brain barrier breakdown compared with normoglycemia. Postischemic blood-brain barrier disruption may play an important role in the pathogenesis of increased brain damage associated with systemic hyperglycemia.     

Characterization of a membrane calcium pathway induced by rotavirus infection in cultured cells

Some viruses induce changes in membrane permeability during infection. We have shown previously that the porcine strain of rotavirus, OSU, induced an increase in the permeability to Na+, K+, and Ca2+ during replication in MA104 cells. In this work, we have characterized the divalent cation entry pathway by measuring intracellular Ca2+ in fura-2-loaded MA104 and HT29 cells in suspension. The permeability to Ca2+ and other cations was evaluated by the change of the intracellular concentration following an extracellular cation pulse. Rotavirus infection induced an increase in permeability to Ca2+, Ba2+, Sr2+, Mn2+, and Co2+. The rate of cation entry decreased over time as the intracellular concentration increased during the first 20 s. This indicates that regulatory mechanisms, including channel inactivation, are triggered. La3+ did not enter the cell and blocked the entry of the divalent cations in a dose-dependent manner. Metoxyverapamil (D600), a blocker of L-type voltage-gated channels, partially inhibited the entry of Ca2+ in virus-infected MA104 and HT29 cells. The results suggest that rotavirus infection of cultured cells activates a cation channel rather than nonspecific permeation through the plasma membrane. This activation involves the synthesis of viral proteins through mechanisms yet unknown. The increase in intracellular Ca2+ induced by the activation of this channel may be related to the increase in cytoplasmic and endoplasmic reticulum Ca2+ pools required for virus maturation and cell death.     

Permeability change and brain tissue damage after intracarotid administration of cisplatin studied by double-tracer autoradiography in rats

The present study was designed to find the reliable parameter(s) for the detection of early neurotoxicity following intracarotid (IC) administration of cisplatin. IC administration was performed for 60 minutes in female Wistar rats derived into four groups according to the dose given (1 mg, 1.2 mg, and 1.5 mg of cisplatin, and normal saline in control rats). Blood-brain barrier (BBB) permeability and local cerebral blood flow (LCBF) were measured by a double-tracer autoradiography technique using 1-[14C]-alpha-aminoisobutyric acid (14C-AIB) and 4-[18F] fluoroantipyrine (18F-FAP), respectively. Blood chemistry and neuropathology were also examined. BBB permeability was increased only on the ipsilateral side. This increase was dose-dependent, preceded the brain necrosis, and was statistically significant in the hypothalamus (1.2 mg group), auditory cortex and caudoputamen (1.5 mg group). Renal dysfunction was often observed. The changes in the LCBF did not occur until brain necrosis was noticeable. These findings demonstrate that the increase in the BBB permeability provides a sensitive and reliable indication of an early toxicity to brain tissue following IC administration of cisplatin.     

Results of initial surgery and adjuvant chemotherapy in treating small-cell lung cancer

The changes in the intestinal mucosal permeability were observed by quantitatively assessing plasma to luminal clearance of 99mTc-labeled DTPA, and the influence of platelet activating factor (PAF) on it was investigated. The results showed that intestinal permeability was significantly elevated after severe burn and was positively correlated with increase in PAF in the intestinal tissue (r = 0.94, P < 0.01). PAF antagonist therapy could significantly attenuate postburn intestinal mucosal permeability. It is concluded that PAF is one of the important factors causing increased intestinal permeability after severe burn.     

Mouse microglial cells express a plasma membrane pore gated by extracellular ATP

We have investigated responses to extracellular ATP (ATPe) in the microglial cell lines N9 and N13 and in freshly isolated mouse microglial cells. Upon stimulation with this nucleotide, N9 and N13 cells underwent an increase in the cytoplasmic free Ca2+ concentration ([Ca2+]i), a sustained depolarization of the plasma membrane, and an uptake of extracellular markers such as ethidium bromide and lucifer yellow; increases in plasma membrane permeability were paralleled by striking morphologic changes. ATPe, as well as other nucleotides, activated a spiking Ca2+ release from intracellular stores; however, only ATPe was also able to cause a massive transmembrane Ca2+ influx. The ATP analogue 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) triggered a sustained Ca2+ influx accompanied by little release from stores. The ATP derivative oxidized ATP (oATP) strongly inhibited Ca2+ influx, minimally affecting Ca2+ release. From ATPe-sensitive microglial cell lines, we selected several ATPe-resistant clones that showed complete lack of ATPe-mediated plasma membrane permeability changes, although they retained the Ca2+ mobilization response from intracellular stores. ATPe-dependent plasma membrane permeability changes were also greatly reduced in growth-arrested microglial cells. Finally, ATPe triggered IL-1 beta release from wild-type but not ATPe-resistant microglial cells. These results show that microglial cells express at least two purinergic receptor subtypes, metabotropic (P2Y) and ionotropic (P2Z), and that the latter is modulated during cell cycle and coupled to IL-1 beta release.     

Filtering properties of highly porous materials prepared from iron powders with nonspherical particles

Conclusions We have shown that the method for preparing the initial powder has an effect on the permeability of the porous material.Other conditions being equal, the permeability is somewhat lower in specimens prepared from reduced powder than with fluidized and spherical powder. However, the possibility of using reduced powder to make components with a higher porosity and hence with a higher permeability makes use of this powder desirable.An increase in porosity of the material from 30 to 55% leads to an increase in permeability from 0.6 to 11.0 liter/min·cm² for a pressure drop of 0.3 kg/cm².A change in thickness of the specimen from 0.5 to 3 mm reduces the permeability by a factor of 2.5–6, and a change in the particle size from 60 to 110 increases the permeability by more than 1.3- to 1.6-fold.A comparison of filters with the same degree of purification, made from spherical and nonspherical powders, shows that they have approximately the same transmission capacity.The data obtained for the filtering capacity of a porous material as a function of the particle size of the powder, the wall thickness, and pressure drop can serve as a basis for selecting the characteristics of a material as a function of the actual design requirements.     

Experimental study of venous circulatory disturbance by dural sinus occlusion

Using a newly devised model of dural sinus occlusion, we investigated the pathophysiology of venous haemorrhage as well as venous circulatory disturbance. The superior sagittal sinus (SSS) and diploic veins (DV) were occluded in 16 cats. Intracranial pressure (ICP), cerebral blood volume (CBV) and regional cerebral blood flow (rCBF) were measured for 12 hours after the occlusion. At the end of the experiment, cerebral water content was estimated. In another 8 cats additional occlusions of cortical veins were carried out. In both groups, the blood-brain barrier permeability was evaluated with Evans blue or horseradish peroxidase. The SSS and DV occlusion produced a significant increase in ICP and CBV concomitant with a significant decrease in rCBF. Cerebral water content also increased significantly. However, there was no transition of Evans blue and horseradish peroxidase through the cerebral vessels, and no haemorrhages could be observed. In contrast, the additional occlusion of cortical veins produced haemorrhagic infarctions with Evans blue extravasation in 6 out of the 8 cats. These data suggest that dural sinus occlusion may lead to an increase in CBV and cerebral water content resulting in intracranial hypertension and decreased rCBF. The brain oedema in this model seemed to be mainly hydrostatic oedema, and might also be contributed by cytotoxic oedema. The additional occlusion of cortical veins might be essential in the development of haemorrhage in this model, and the blood-brain barrier was also disrupted in these areas.     

Effect of fibronectin amount and conformation on the strength of endothelial cell adhesion to HEMA/EMA copolymers

P-Glycoprotein (P-gp) and multidrug resistance protein (MRP) are plasma membrane associated proteins which can confer multidrug resistance (MDR) to cancer cells by lowering the intracellular amount of drug. Although clinical trials with MDR-reverting agents have been initiated, not much attention has been paid to blood components which may modulate the activity of P-gp or MRP. The present investigation was performed to identify and characterize blood components which may influence the drug content and the drug cytotoxicity of MDR cells. Human plasma, from healthy volunteers, was tested for its effects on the daunorubicin (DNR) accumulation and cytotoxicity in the MDR cell lines SW-1573/2R160 (2R160) and GLC4/ADR containing P-gp and MRP, respectively. The data were compared to the effects observed in wild-type cells. MDR-modifying plasma components were isolated by extraction procedures and characterized using ultrafiltration, high-performance liquid chromatography (HPLC) and mass spectrometry. An increase in the proportion of plasma in the culture medium led to a reduction of the ratio between the DNR content of wild-type and corresponding MDR cells. At 100% plasma we observed an increase in the cellular DNR content of 2R160 cells, which was 10-30% (median 18%) of the maximum possible increase induced by well-known MDR-reverting agents, such as verapamil (for GLC4/ADR cells: 10-20%, median 15%). The DNR cytotoxicity in MDR cells also increased with an increasing amount of plasma included in the culture media. There was neither an increase in the cellular DNR content nor an effect on the DNR cytotoxicity in wild-type cells. Plasma extract analysis by HPLC showed a major peak which increased the DNR content of MDR cells. The HPLC column retention time of this fraction was identical to that of a standard of cortisol and it was further confirmed to be cortisol using mass spectrometry. Moreover, inclusion of a standard of cortisol in culture media induced a similar effect. We analyzed the data for one of the plasma pools and found that blood cortisol was responsible for the MDR-modulating effect only for 35% of the effect of 100% plasma. Other plasma components were responsible for the remaining modulation effect on MDR cells. In conclusion, the DNR pumping activity of P-gp and MRP is inhibited by human plasma, resulting in 10-30% of the maximum possible increase in cellular drug content. Based on cellular pharmacokinetic calculations this percentage will most likely increase at clinical levels of drug resistance (reaching 40-50%). In one sample blood cortisol accounted for 35% of the effect of plasma on the DNR content in MDR 2R160 cells. These data show the need for additional studies to test plasma samples for their MDR modulating effects before the administration of MDR-reverting agents in chemotherapy. The data suggest that the effectiveness of chemotherapeutic drugs may be enhanced when administered in accordance with the circadian peak of endogenous corticoids.     

Acetaldehyde-induced increase in paracellular permeability in Caco-2 cell monolayer

Evidence indicates that endotoxin-mediated liver injury plays an important role in the pathogenesis of alcoholic liver disease. Elevated plasma endotoxin level in alcoholics is suggested to be caused by enteric bacterial overgrowth and/or increased intestinal permeability to endotoxin. In this study, the effect of ethanol and acetaldehyde on the paracellular permeability was evaluated in Caco-2 cell monolayers. Ethanol was administered into the incubation medium, whereas acetaldehyde was administered by exposing cell monolayers to vapor phase acetaldehyde, or by direct administration of an acetaldehyde generating system (AGS), ethanol + NAD+ + alcohol dehydrogenase. Paracellular permeability was assessed by measuring transepithelial electrical resistance (TER), sodium chloride dilution potential, and unidirectional flux of D-[2-(3)H]mannitol. Administration of ethanol up to 900 mM produced no significant effect on paracellular permeability. Vapor phase acetaldehyde, generated from 5 to 167 mM acetaldehyde solutions in neighboring wells, resulted in a time- and dose-dependent increase in acetaldehyde concentration (99 to 760 microM) in the buffer bathing cell monolayer. Acetaldehyde induced a reduction of TER and dilution potential, and an elevation of mannitol flux in a time and concentration-related manner, without affecting the ability of cells to exclude trypan blue. Removal of acetaldehyde after 1, 2, or 4 hr treatment and subsequent incubation in the absence of acetaldehyde resulted in a time-dependent reversal of TER to baseline values. Administration of AGS also reduced TER and dilution potential, associated with an increase in mannitol flux. This effect of AGS was prevented by 4-methylpyrazole, an alcohol dehydrogenase inhibitor. These results show that acetaldehyde, but not ethanol, reversibly increases the paracellular permeability of Caco-2 cell monolayer.     

Brain uptake of mannitol and sucrose after cerebral ischemia: effect of hyperglycemia

The effect of 10 min cerebral ischemia on blood-brain barrier permeability to mannitol and sucrose was evaluated in normo- and hyperglycemic rats. In the period immediately after ischemia (1-4 min) the PS (permeability-surface area product) for mannitol was 159% +/- 75 of control (0.17 +/- 0.02 mg/100 g min) in the hyperglycemic rats (plasma glucose 8 mM) and 204% +/- 30 of control (0.09 +/- 0.02 mg/100 g min) in the hyperglycemic rats (plasma glucose 28 mM). Two hours after ischemia, PS for mannitol returned to the control levels in the normoglycemic rats and remained elevated in hyperglycemic animals. The mannitol/sucrose ratios-2.3 +/- 0.4 in normoglycemic rats and 2.6 +/- 0.1 in hyperglycemic rats-remained unchanged after ischemia. As there was no significant difference in the effects of ischemia on normo- and hyperglycemic rats, it was concluded that the deleterious effect of hyperglycemic on clinical recovery after cerebral ischemia in rats (Siemkowicz & Hansen 1978) is not related to enhancement of BBB damage.     

Expression of vascular endothelial growth factor (VEGF) and its receptors (Flt-1 and Flk-1) following permanent and transient occlusion of the middle cerebral artery in the rat

Vascular endothelial growth factor (VEGF) is a known endothelial mitogen and a potent enhancer of vascular permeability although its role in focal cerebral ischemia is still not completely understood. The present report describes the immunohistochemical distribution of VEGF and its 2 receptors, Flt-1 and Flk-1 at day 1 and 3 following permanent and transient middle cerebral artery occlusion (MCAO) in the rat. A bilateral increase in VEGF immunoreactivity, particularly in neurons and blood vessels, was seen in both the experimental designs by day 1. By day 3, the immunoreactivity was restricted chiefly to the lesion side, where reaction was most prominent in the border zones of the infarcts. Immunoreaction to VEGF was more pronounced in cases of permanent MCAO than in transient MCAO. Flt-1 reaction was increased in neurons, glial and endothelial cells after both transient and permanent MCAO. Immunoreactivity to Flk-1 was prominent in glial cells and was present to some extent in endothelial cells. These findings indicate an early upregulation of VEGF and its receptors after permanent as well as transient focal cerebral ischemia in the rat.