Biomedical subjects

A L Betz

Publications and source records attributed to A L Betz.

At least 19 recordsLinked to original sources

PubMed1996

The role of the coagulation cascade in brain edema formation after intracerebral hemorrhage.

The coagulation cascade has a potential role in brain edema formation due to intracerebral hemorrhage. In this study blood and other solutions were injected stereotactically into the right basal ganglia in rats. Twenty-four hours following injection, brain water and ion contents were measured to determine the amount of brain edema. Intracerebral blood resulted in an increase in brain water content. The amount of brain edema surrounding the intracerebral hematoma was reduced by a thrombin inhibitor N alpha-(2-Naphthalenesulfonylglycyl)-4-amidino-DL-phenylalaninep iperidide, (alpha-NAPAP) infused into the hematoma after the clot had been allowed to solidify. The inhibitor did not alter the actual size of the clot mass. An artificial clot composed of fibrinogen, thrombin, and styrene microspheres also produced brain edema. A fibrin clot led to edema formation even in the absence of mass effect provided by the microspheres. The single component responsible for production of brain edema in all these models was thrombin. The edema was formed in response to a fibrinogen-independent pathway. These results indicate that the coagulation cascade is involved in brain edema that develops adjacent to an intracerebral hematoma.

Animals↗

PubMed1996

Mechanisms of sodium transport at the blood-brain barrier studied with in situ perfusion of rat brain.

The mechanism of unidirectional transport of sodium from blood to brain in pentobarbital-anesthetized rats was examined using in situ perfusion. Sodium transport followed Michaelis-Menten saturation kinetics with a Vmax of 50.1 nmol/g/min and a Km of 17.7 mM in the left frontal cortex. The kinetic analysis indicated that, at a physiologic sodium concentration, approximately 26% of sodium transport at the blood-brain barrier (BBB) was carrier mediated. Dimethylamiloride (25 microM), an inhibitor of Na+/H+ exchange, reduced sodium transport by 28%, whereas phenamil (25 microM), a sodium channel inhibitor, reduced the transfer constant for sodium by 22%. Bumetanide (250 microM) and hydrochlorothiazide (1.5 mM), inhibitors of Na(+)-K(+)-2Cl-/NaCl symport, were ineffective in reducing blood to brain sodium transport. Acetazolamide (0.25 mM), an inhibitor of carbonic anhydrase, did not change sodium transport at the BBB. Finally, a perfusate pH of 7.0 or 7.8 or a perfusate PCO2 of 86 mm Hg failed to change sodium transport. These results indicate that 50% of transcellular transport of sodium from blood to brain occurs through Na+/H+ exchange and a sodium channel in the luminal membrane of the BBB. We propose that the sodium transport systems at the luminal membrane of the BBB, in conjunction with Cl-/HCO3- exchange, lead to net NaCl secretion and obligate water transport into the brain.

Amiloride↗

PubMed1996

Edema from intracerebral hemorrhage: the role of thrombin.

The mechanism by which intracerebral hemorrhage leads to the formation of brain edema is unknown. This study assesses the components of blood to determine if any are toxic to surrounding brain. Various solutions were infused stereotactically into the right basal ganglia of rats. The animals were sacrificed 24 hours later; brain edema and ion contents were measured. Whole blood caused an increase in brain water content and ion changes consistent with brain edema. Concentrated blood cells, serum from clotted blood, and plasma from unclotted blood all failed to provoke edema formation when infused directly into the brain. On the other hand, activation of the coagulation cascade by adding prothrombinase to plasma did produce brain edema. The edema response to whole blood could be prevented by adding a specific thrombin inhibitor, hirudin, to the injected blood. This study indicates that thrombin plays an important role in edema formation from an intracerebral blood clot.

Animals↗

PubMed1996

Thrombin-soaked gelatin sponge and brain edema in rats.

Previous work from this laboratory has shown that injection of thrombin into rat basal ganglia causes brain edema. This study investigates the effect on rat brain of thrombin-soaked gelatin sponge (used for intraoperative hemostasis in clinical situations) at a concentration similar to that used in humans. Three models were developed to evaluate this effect. In the first model, a gelatin sponge soaked with vehicle or thrombin (100 U/cm3) was placed on the intact pia of the right frontal lobe in rats without cortical lesions. In the second model, frontal cortex was excised (3 mm3) and the exposed brain was cauterized with electrocoagulation. Gelatin sponge was soaked with vehicle or thrombin (1000, 100, 10, or 1 U/cm3) and placed in the lesion site. In the third model, hirudin, a specific thrombin antagonist, was added to the thrombin-soaked gelatin sponge and placed in a similar cortical lesion to determine if the observed effects were specific to thrombin. The dose-response range for thrombin was determined qualitatively by magnetic resonance (MR) imaging and quantitatively by brain edema formation 24 hours after exposure. We found no edema in the cortically intact rats. The rats given cortical lesions developed significant edema when subjected to 1000, 100, and 10 U/cm3 thrombin as seen on MR imaging and at 100 and 10 U/cm3 thrombin as revealed by wet/dry weight and ion studies of brain tissue. Topical hirudin prevented thrombin-induced edema. It is concluded that thrombin-soaked gelatin sponges cause or enhance significant brain edema in rats at concentrations typically used for human neurosurgery.

Administration, Topical↗

PubMed1996

Alterations in cerebral endothelial cell function in ischemia.

As summarized in Fig. 2, nearly all aspects of brain microvascular endothelial cell function may be affected by ischemia. These alterations not only interfere with BBB functions which are critical for protection of the brain, but they may also lead to the production of substances that are directly toxic to the brain. Thus, the cerebrovascular endothelial cell appears to be both a target and participant in the processes that produce damage in ischemic brain.

Animals↗

PubMed1995

Developmental changes in blood-brain barrier potassium permeability in the rat: relation to brain growth.

1. The potassium permeability of the blood-brain barrier (BBB) was determined in anaesthetized rats aged between 21 days gestation and adult using 86Rb+ as a marker for potassium. 2. The brain influx rate constant for 86Rb+ was high in fetal cortex at 21 days gestation (42.5 +/- 4.3 microliters g-1 min-1) but had decreased markedly by just after birth (12.2 +/- 0.6 microliters g-1 min-1). There was a further, gradual, postnatal decline to 7.0 +/- 0.3 microliters g-1 min-1 by 50 days after birth. 3. Developmental changes in passive BBB permeability were examined over the same age range using 14[C]urea. These studies showed similar developmental changes in influx rate to those found for 86Rb+. Specifically, a marked perinatal decline followed by a more gradual postnatal fall. Thus, the changes in potassium permeability probably reflect a decrease in the BBB paracellular leak during development. 4. The changes in BBB permeability coincide with changes in the rate of brain growth and the associated rate of brain potassium accumulation. As the potassium permeability properties of the adult BBB would provide insufficient potassium influx to meet the requirement associated with fetal brain growth, it is suggested that need for potassium may be the reason for the greater BBB permeability early in development.

Animals↗

PubMed1995

Blood-brain barrier taurine transport during osmotic stress and in focal cerebral ischemia.

Little is known about blood to brain taurine transport despite substantial evidence suggesting a role of taurine in brain volume regulation during osmotic stress or conditions inducing cell swelling, such as ischemia. We have made measurements of the taurine influx rate constant (K1) with [3H]taurine in three conditions: raised plasma taurine concentrations induced by infusion with 50 mM taurine (10 microliters/100 g/min); osmotic stress induced by i.p. injections of 1.5 M NaCl (2 ml/100 g) or distilled water (10 ml/100 g); and 4 h of middle cerebral artery occlusion (MCAo). In rats with MCAo, additional determinations were made of tissue water and taurine contents, and blood-brain barrier passive permeability with [3H]alpha-aminoisobutyric acid. Taurine infusion increased plasma taurine from 110 +/- 63 microM (SD) to 407 +/- 63 (p < 0.001) and decreased taurine K1 at the blood-brain barrier by 70% (p < 0.001), signifying saturable uptake that maintained unidirectional influx constant. Similarly, although hypo- and hyperosmolality increased and decreased plasma taurine concentration, respectively, a reciprocal relationship between K1 and plasma taurine in these experiments ensured that unidirectional fluxes of taurine into brain were unchanged by osmotic stress. During MCAo, the taurine K1 was reduced 80% in the ipsilateral ischemic tissue compared with the contralateral nonischemic tissue (p < 0.001). This decline may be due to a release of taurine into the brain circulation, because there was a concomitant loss of tissue taurine of 7.4 +/- 2.4 mmol/g dry weight (p < 0.05). Alternately, if taurine uptake is sodium dependent, the decline might reflect a disruption of the endothelial sodium gradient.

Aminoisobutyric Acids↗

PubMed1995

Mechanisms of brain ion homeostasis during acute and chronic variations of plasma potassium.

Brain and CSF potassium concentrations are well regulated during acute and chronic alterations of plasma potassium. In a previous study, we have shown that during chronic perturbations, regulation is achieved by appropriate adaptation of potassium influx, but that the degree of such adaptation during acute perturbations is much less. To elucidate further potential regulatory mechanisms, rats were rendered acutely or chronically hyper- or hypokalemic (range 2.7-7.6 mM). Measurements were made of brain and CSF water and ion contents to examine whether regulation occurred by modulation of K+ uptake into parenchymal cells. Furthermore, the permeability-surface area products (PSs) of 22Na+ were determined, because changes in K+ efflux fia Na+,K(+)-ATPase on the brain-facing side of the blood-brain barrier might be reflected in modified Na+ permeability. Brain and CSF K+ concentrations and Na PS were all independent of chronic changes in plasma K+ and acute hypokalemia, suggesting that neither modulation of parenchymal K+ uptake nor K+ efflux via the Na+,K(+)-ATPase is involved in extracellular K+ regulation in these conditions. In contrast, Na PSs were increased by 40% (p < 0.05) in acute hyperkalemia. This was accompanied by a slight loss of tissue K+ and water from the intracellular space. These results suggest that increased potassium influx in acute hyperkalemia is compensated by stimulation of K+ efflux via Na+,K(+)-ATPase. A slight degree of overstimulation, as indicated by a net loss of tissue K+, leads us to hypothesize that other factors, apart from the kinetic characteristics of Na+,K(+)-ATPase, may regulate this enzyme at the blood-brain barrier.

Animals↗

PubMed1995

Attenuation of stroke size in rats using an adenoviral vector to induce overexpression of interleukin-1 receptor antagonist in brain.

Adenoviruses have been proposed as potential vectors for gene therapy in the central nervous system, but there are no reports of their use in the treatment of a brain disease. Because central administration of interleukin-1 receptor antagonist protein (IL-1ra) reduces ischemic brain damage, we determined whether a recombinant adenovirus vector carrying the human IL-1ra cDNA (Ad.RSVIL-1ra) could be used to ameliorate brain injury in permanent focal ischemia. Groups of six rats received intraventricular injections of Ad.RSVIL-1ra or a control adenovirus containing the Escherichia coli beta-galactosidase gene (Ad.RSVlacZ). Histochemical staining for beta-galactosidase 5 days after virus injection indicated that transgene expression was confined primarily to the cells lining the ventricle. The concentrations of IL-1ra injected animals, achieving levels of 9.1 +/- 3.3 ng/g in brain and 23.7 +/- 22.5 ng/ml in CSF. In these animals, cerebral infarct volume resulting from 24 h of permanent middle cerebral artery occlusion was reduced 64%. These studies demonstrate that adenoviral vectors can be used to deliver genes that attenuate brain injury.

Adenoviridae↗

PubMed1995

Inhibition of neutral amino acid transport across the human blood-brain barrier by phenylalanine.

The delivery of large neutral amino acids (LNAAs) to brain across the blood-brain barrier (BBB) is mediated by the L-type neutral amino acid transporter present in the membranes of the brain capillary endothelial cell. In experimental animals, the L-system transporter is saturated under normal conditions, and therefore an elevation in the plasma concentration of one LNAA will reduce brain uptake of others. In this study, we used positron emission tomography (PET) to determine the effect of elevated plasma phenylalanine concentrations on the uptake of an artificial neutral amino acid, [11C]-aminocyclohexanecarboxylate ([11C]ACHC), in human brain. PET scans were performed on six normal male subjects after an overnight fast and again 60 min after oral administration of 100 mg/kg of phenylalanine. The plasma phenylalanine concentration increased by an average of 11-fold between the first and second scans. This increase produced a reduction in [11C]ACHC uptake in all brain regions but not in scalp. The mean +/- SD influx rate constant for whole brain decreased after phenylalanine ingestion from 0.036 +/- 0.002 to 0.019 +/- 0.004 ml/g/min. Kinetic analysis of the effect of plasma phenylalanine concentration on the rate of [11C]ACHC uptake is compatible with a model of competitive inhibition so that large increases in the concentration of one LNAA in plasma will reduce the brain uptake of other LNAAs across the human BBB.

Adult↗

PubMed1995

Chronic central potassium infusion prevents deoxycorticosterone-salt hypertension in rats.

Although it has long been established that cerebrospinal fluid potassium concentration (CSF [K]) is very tightly regulated, it has been reported that rats made hypertensive by central infusions of aldosterone have significantly lower CSF [K] compared with normotensive controls. We investigated whether reduced CSF [K] is also present in another animal model of hypertension, the deoxycorticosterone acetate (DOCA)-salt rat, and we hypothesized that chronic intracerebroventricular (IVT) infusion of potassium with miniosmotic pumps might attenuate the rise in blood pressure observed in these rats. DOCA-salt rats without IVT infusions or with control CSF infusions (0.5 microliter/h of 2.9 mM K for 2 wk) had a significantly increased systolic blood pressure and a significantly lower CSF [K] compared with their respective sham groups. In contrast, DOCA-salt rats receiving IVT infusions with elevated [K] (10, 30, or 150 mM) had significantly lower blood pressures compared with those receiving control CSF. They also did not exhibit decreased CSF [K] compared with their respective sham groups. At 10 and 150 mM K, the blood pressure rise in DOCA-salt rats was not significantly different from shams. At 30 mM K, there was a slight, but significant, increase in blood pressure in the DOCA-salt rats compared with their shams, but this rise was still much less than in DOCA-salt rats infused with 2.9 mM K. Infusions with elevated [K] had no effect on blood pressure in the sham animals. These studies suggest that altered brain potassium homeostasis may play an important role in the development of DOCA-salt hypertension.

Animals↗

PubMed1995

Preischemic but not postischemic zinc protoporphyrin treatment reduces infarct size and edema accumulation after temporary focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE: Zinc protoporphyrin (ZnPP) has multiple actions. It is an interleukin-1 antagonist as well as a hemeoxygenase inhibitor. Interleukin-1 is produced in ischemic brain and probably contributes to ischemic injury, although the role of heme oxygenase during ischemia is unknown. Whether ZnPP treatment is more effective before or after ischemia, as well as whether it is more protective in permanent or temporary cerebral ischemia, is also unknown. Therefore, we investigated the effect of ZnPP on infarction size and edema in a rodent model of temporary and permanent focal cerebral ischemia. METHODS: Two groups of adult male Sprague-Dawley rats were pretreated with either 50 mg/kg ZnPP IP or saline and subjected to permanent middle cerebral artery occlusion 30 minutes later. Four additional groups of animals were subjected to 2 hours of temporary middle cerebral artery occlusion followed by 22 hours of reperfusion. Two of these groups were pretreated 30 minutes before middle cerebral artery occlusion with either 50 mg/kg ZnPP IP or saline. The other groups received ZnPP at either 2 or 4 hours after middle cerebral artery occlusion. Regional cerebral blood flow in the ischemic cortex was monitored with laser Doppler flowmetry. Cerebral infarct size and brain water were measured 24 hours after the onset of either form of ischemia. RESULTS: Regional cerebral blood flow after occlusion was approximately 13% to 20% of baseline after either permanent or temporary ischemia. ZnPP had no effect on regional cerebral blood flow, infarct size, or edema formation in permanent ischemia. In contrast, pretreatment significantly reduced infarct size (17.2 +/- 6.6% in controls versus 6.2 +/- 2.9% in pretreated rats) and edema formation (center zone, 4.00 +/- 0.71% water in controls versus 1.18 +/- 0.26% water in pretreated rats) in the model of temporary ischemia, but treatment after occlusion had no effect. CONCLUSIONS: ZnPP treatment protected the brain when administered early in the temporary ischemia model.

Animals↗

PubMed1995

Gene expression from recombinant viral vectors in the central nervous system after blood-brain barrier disruption.

Direct intracerebral injection of recombinant adenoviral vectors within the brain parenchyma or the ventricular system results in a limited volume of distribution of virus, as demonstrated by transgene expression. Global delivery to the central nervous system may increase the use of these vectors but only if the viral vectors can cross the blood-brain barrier and result in transduction of the underlying cells. This short-term study examines whether osmotic disruption with mannitol can result in sufficient opening of the vascular endothelium to allow for passage of replication-defective adenovirus containing the Escherichia coli beta-galactosidase gene (lacZ). Virus was injected into the carotid artery of rats after blood-brain barrier disruption with intracarotid hypertonic mannitol, and the animals were killed and analyzed after 4 days. Histochemical analysis and electron microscopy confirmed expression of the E. coli lacZ gene in the pericapillary astrocytes of the ipsilateral cerebral cortex and deep grey matter. Furthermore, the extent of gene transfer and expression correlated with the degree of barrier opening, as measured by Evans blue staining. Transgene expression was not seen in control animals that received intracarotid saline before recombinant virus injection. These data demonstrate, for the first time, that blood-brain barrier disruption can allow for the delivery of functional viral vectors to the central nervous system.

Adenoviridae↗

PubMed1995

Intracerebral infusion of thrombin as a cause of brain edema.

Purified thrombin from an exogenous source is a hemostatic agent commonly used in neurosurgical procedures. The toxicity of thrombin in the brain, however, has not been examined. This study was performed to assess the effect of thrombin on brain parenchyma, using the formation of brain edema as an indicator of injury. Ten microliters of test solution was infused stereotactically into the right basal ganglia of rats. The animals were sacrificed 24 hours later, and the extent of brain edema and ion content were measured. Concentrations of human thrombin as low as 1 U/microliter resulted in a significant increase in brain water content. Rats receiving 10 U/microliters had a mortality rate of 33% compared to no mortality in the groups receiving smaller doses. Thrombin-induced brain edema was inhibited by a specific and potent thrombin inhibitor, hirudin. A medical grade of bovine thrombin commonly used in surgery also caused brain edema when injected at a concentration of 2 U/microliters. Edema formation was prevented by another highly specific thrombin inhibitor, N alpha-(2-Naphthalenesulfonylglycyl)-4-DL-phenylalaninepiperidid e (alpha-NAPAP). Thrombin-induced brain edema was accompanied by increases in brain sodium and chloride contents and a decrease in brain potassium content. Changes in brain ions were inhibited by both hirudin and alpha-NAPAP, corresponding to the inhibition of brain water accumulation. This study shows that thrombin causes brain edema when infused into the brain at concentrations as low as 1 U/microliter, an amount within the range of concentrations used for topical hemostasis in neurosurgery.

Animals↗

PubMed1994

Transport of alpha-aminoisobutyric acid across the blood-brain barrier studied with in situ perfusion of rat brain.

Transport of alpha-aminoisobutyric acid (AIB) from blood to brain in pentobarbital-anesthetized rats was examined using in situ perfusion. In situ perfusion with washed sheep red blood cells allowed the precise control of the composition of the perfusate that was necessary for a detailed examination of the transport of AIB. Retrograde perfusion at 4 ml/min through the left external carotid artery with oxygenated, artificial blood (hematocrit = 0.3) maintained a normal electroencephelogram during a 10 min experiment. The perfusate cerebral blood flow, at a value of 1.2 +/- 0.1 ml/g/min, and the perfusate cerebral plasma volume, at a value of 5.4 +/- 1.9 microliter/g, in the left frontal cortex were within the range of reported in vivo values. The in situ PS product for AIB (3.8 +/- 0.4 microliter/g/min) was higher than the value observed in vivo. AIB uptake was reduced to the in vivo value by 2 mM phenylalanine (1.3 +/- 0.3 microliter/g/min) and equally well by a mixture of neutral amino acids at their normal plasma concentrations but was unaffected by 2 mM methyl-AIB or removal of sodium from the perfusate. A kinetic analysis showed that the apparent Ki for phenylalanine inhibition of AIB transport was 19.8 +/- 4.9 microM. Thus, although AIB has affinity for the large neutral amino acid carrier in the blood-brain barrier, brain uptake by this mechanism in vivo is negligible due to competition by other amino acids in the plasma.

Amino Acids↗

PubMed1994

The effects of blood or plasma clot on brain edema in the rat with intracerebral hemorrhage.

The causes and characteristics of the brain edema which forms adjacent to an acute intracerebral hemorrhage (ICH) have not been explored thoroughly. This study was designed to examine the edema process in rat brain provoked by two different blood clot components. An intracerebral clot was produced by stereotactic injection of 100 microl of either blood (bICH) or cryoprecipitate/thrombin (pICH) into the right caudate nucleus. Water, Na+, K+, and Cl- contents were measured at 0, 4.24, 48, and 72 h after instillation of the clot. During the first 24 h, the water content of the ipsilateral caudate nucleus and cortex gradually increased in both groups. By 48 h brain edema was more severe in the bICH compared to that with pICH in the ipsilateral basal ganglia and cortex. The edema formation was accompanied by significant increase in sodium and chloride, as well as a decrease in potassium content by 48 h and sustained to 72 h. These results suggest that both blood and plasma clots can cause brain edema, but a plasma clot is less damaging than a blood clot in the immediate vicinity of the mass.

Animals↗

PubMed1994

Riboflavin reduces edema in focal cerebral ischemia.

Oxidized irwN has been proposed as a mediator of the free radical-induced damage that occurs during cerebral ischemia. Dihydroriboflavin, a compound produced from riboflavin (B2) by NADPH-dependent flavin reductase, rapidly reduces oxidized iron. Since treatment with riboflavin offers protection from ischemic injury in other tissues, we tested the effect of pretreatment with B2 on brain edema formation during focal ischemia. Two different models of middle cerebral artery occlusion (MCAO) in rats were tested: transcranial electrocautery and intracarotid occlusion with a nylon thread. Groups of 6-8 animals were treated with 7.5 mg of B2/kg or saline vehicle 1 h before MCAO and brain water content was determined after 4 h of ischemia. Pretreatment with B2 reduced total hemisphere edema formation from 0.37 +/- 0.05 to 0.19 +/- 0.05 mg/g dry wt. (48% protection, p < 0.01) following transcranial MCAO. Edema was greater following MCAO with the intra-carotid thread (0.54 +/- 0.05 ml/g) but protection by B2 was less (21%). We conclude that pretreatment with B2 reduces ischemic brain injury, perhaps by reacting with oxidized iron. However, the larger stroke produced by the thread MCAO method makes it more difficult to observe protection following brief ischemia in this model.

Animals↗

PubMed1994

Blood-brain barrier permeability and brain concentration of sodium, potassium, and chloride during focal ischemia.

Brain edema formation during the early stages of focal cerebral ischemia is associated with an increase in both sodium content and blood-brain barrier (BBB) sodium transport. The goals of this study were to determine whether chloride is the principal anion that accumulates in ischemic brain, how the rate of BBB transport of chloride compares with its rate of accumulation, and whether the stimulation seen in BBB sodium transport is also seen with other cations. Focal ischemia was produced by occlusion of the middle cerebral artery (MCAO) in anesthetized rats. Over the first 6 h after MCAO, the amount of brain water in the center of the ischemic cortex increased progressively at a rate of 0.15 +/- 0.02 (SE) g/g dry wt/h. This was accompanied by a net increase in brain sodium (48 +/- 12 mumol/g dry wt/h) and a loss of potassium (34 +/- 7 mumol/g dry wt/h). The net rate of chloride accumulation (16 +/- 1 mumol/g dry wt/h) approximated the net rate of increase of cations. Three hours after MCAO, the BBB permeability to three ions (22Na, 36Cl, and 86Rb) and two passive permeability tracers ([3H]alpha-aminoisobutyric acid ([3H]AIB) and [14C]urea) was determined. Permeability to either passive tracer was not increased, indicating that the BBB was intact. The rate of 36Cl influx was 3 times greater and the rate of 22Na influx 1.8 times greater than their respective net rates of accumulation in ischemic brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗