Ischemia In Cats Research Articles

Effect of Water-Soluble Echinochrome Analog on Arrhythmia Severity in Experimental Model of Acute Myocardial Ischemia.

The effects of therapeutic or preventive-therapeutic administration of water-soluble echinochrome analog U-441 on arrhythmia severity assessed by a set of myocardial spatio-temporal depolarization and repolarization parameters were examined on the model of acute myocardial ischemia in cats. Coronary occlusion increased activation time and decreased repolarization time in the ischemic zone; in addition, it increased both global and borderline (local) dispersions of repolarization. The linear regression model showed that only activation time values measured at the initial state and at termination of occlusion were associated with total arrhythmia score during ischemia (regression coefficient β=0.338, 95%CI=0.074-0.602, p=0.015 and β=0.720, 95%CI=0.323-1.117, p=0.001, respectively). The study revealed no association between administration of echinochrome analog U-441 and arrhythmia severity.

Neuroprotective effect of mild hypothermia in the temporary brain ischemia in cats

To evaluate the neuroprotective effect of mild hypothermia during temporary focal ischemia in cats. 20 cats underwent middle cerebral artery 60 minutes occlusion and 24 hours reperfusion: 10 under normothermia and 10 under mild hypothermia (32 masculine C). Brain coronal sections 2mm thick were stained with 2,3,5-triphenyltetrazolium hydrochloride, photographed and evaluated with software for volume calculation. Cortical ischemia was found in 7 and basal ganglia ischemia in 8 animals of group 1 and in both regions in 5 animals of group 2 (no difference: p=0.6499 for cortical; p=0.3498 for basal ganglia). No ischemia was found in 5 animals of group 2 and in none of group 1 (significant difference, p=0.0325). The infarct volume was greater in group 1 than 2 (p=0.0433). Mild hypothermia did not interfere with location of ischemia, but it was effective for reducing the infarct volume.

Significant shrinkage of extracellular space during global cerebral ischemia: differences in gray and white matter ischemia.

Brain extracellular space (ECS) provides an important microenvironment for neurons and glial cells. In the present study, we investigated differences in ischemic changes of ECS in gray and white matter during global ischemia in cats (n = 8). Diffusion capacity of tetramethylammonium ion (TMA+, 74.1Da) was evaluated by measuring extracellular TMA+ concentration applied via microdialysis. In both gray and white matter, TMA+ concentration significantly increased within 10 minutes after the induction of ischemia, and sustained during 120 min of ischemia. The increase, however, was slower and smaller in white matter than in gray matter. In other two animals, volume fraction and tortuosity of ECS were determined by iontophoresis during global ischemia. After 30 min of ischemia induction, volume fraction was decreased and tortuosity was increased in both gray and white matter. In white matter, decrease in volume fraction and increase in tortuosity were smaller than in gray matter. The present study demonstrates that cerebral ischemia induces not only significant shrinkage of ECS volume but also restricts molecular diffusion within. Smaller changes of diffusion capacity within white matter ECS during ischemia may be relevant for lower ischemic vulnerability of the region.

Prediction of malignant infarction: perifocal neurochemical monitoring following prolonged MCA occlusion in cats.

Neurochemical monitoring in the ischemic core predicts malignancy in focal ischemia in cats. Since perifocal regions are more suitable for clinical microdialysis (MD) applications, we tested whether monitoring at such site predicts also malignancy.--Laser Doppler (LD) probes, pressure microsensors, and MD/HPLC measured cerebral blood flow (CBF), intracranial pressure (ICP), and extracellular glutamate (Glu), respectively. The middle cerebral artery was occluded (MCAO) for 3 hours followed by 6 hours reperfusion. Additionally, LD measured CBF in ischemic core.--MCAO reduced CBF in the core in all below 25% of control. In animals exhibiting malignancy (eye dilatation during reperfusion), MCAO decreased CBF in the perifocal site to around 35%. CBF primarily recovered following recirculation but decreased thereafter as ICP rose due to progressive edema formation. Glu increased concomitantly. In cats exhibiting a benign course, MCAO decreased CBF in the perifocal site to around 55%. Recirculation normalized CBF, and Glu did not increase. During MCAO, Glu differences between both groups were not significant.--Glu determinations in perifocal sites taken during MCAO do not predict fatal outcome. This contrasts with determinations in the core. After reperfusion, Glu elevation in perifocal sites may serve as a rather late predictor of malignancy.

A new method of inducing selective brain hypothermia with saline perfusion into the subdural space: effects on transient cerebral ischemia in cats.

In this study, we tested brain surface cooling as a new method of inducing selective brain hypothermia, and evaluated its effects on focal cerebral ischemia using a cat model of transient middle cerebral artery (MCA) occlusion. Cats underwent 1 h of MCA occlusion followed by 5 h of reperfusion. Brain surface cooling was induced for 4 h during and after MCA occlusion in the hypothermia group, but not in the normothermia group. Brain surface cooling was performed using saline perfusion into the subdural space. Rectal temperature, brain surface temperature, and deep brain temperature were monitored, and regional cerebral blood flow (rCBF) and somatosensory evoked potential (SEP) were serially measured. After 5 h of reperfusion, water content was also measured. Although the rectal temperature was maintained at about 37 degrees C, the brain surface temperature decreased rapidly to 33 degrees C and was maintained at that temperature. For 3 h following reperfusion, the rCBF was lower in the hypothermia group than in the normothermia group. At 4 and 5 h after reperfusion, the recovery of SEP amplitude was significantly more enhanced in the hypothermia group than in the normothermia group. In the gray matter, the water content was significantly more diminished in the hypothermia group than in the normothermia group. These results demonstrate that our method is useful for protecting the ischemic brain from a transient MCA occlusion. This method may be adapted for neurological surgery.

Effects of hypothermia and rewarming on evoked potentials during transient focal cerebral ischemia in cats

We examined the effects of mild to moderate hypothermia and the influence of rewarming on electrophysiological function using somatosensory evoked potentials (SEPs) in transient focal ischemia in the brain. Nineteen cats underwent 60 min of left middle cerebral artery occlusion under normothermic (36 ° -37 ° C, n = 6) or hypothermic (30 ° -31 ° C, n = 13) conditions followed by 300 min of reperfusion with slow (120 min, n = 6) or rapid (30 min, n = 7) rewarming. Whole-body hypothermia was induced during ischemia and the first 180 min of reperfusion. SEPs and regional cerebral blood flow were measured before and during ischemia and during reperfusion. The specific gravity of gray and white matter was examined as the indicator of edema. During rewarming, SEP amplitudes recovered gradually. After rewarming, SEPs in the normothermic and rapid rewarming groups remained depressed (20%-40% of pre-occlusion values); however, recovery of SEPs was significantly enhanced in the slow rewarming group (p < 0.05). Hypothermia followed by slow rewarming reduced edema in gray and white matter. Rapid rewarming did not reduce edema in the white matter. The recovery of SEPs correlated with the extent of brain edema in transient focal ischemia. Rapid rewarming reduced the protective effect of hypothermia. [Neurol Res 2002; 24: 621-626]

Role of activated platelets in excitation of cardiac afferents during myocardial ischemia in cats

Myocardial ischemia activates cardiac spinal afferents that mediate chest pain and excitatory reflex cardiovascular responses. Platelets are activated during myocardial ischemia and release 5-hydroxytryptamine, which stimulates abdominal spinal afferents. This study investigated the role of activated platelets in excitation of cardiac spinal afferents during ischemia. Platelet-rich plasma (PRP) and platelet-poor plasma (PPP) were obtained from cats and incubated with collagen (2 mg/ml) or thrombin (5 U/ml). We observed reduction of platelets in PRP indicative of platelet activation by collagen and thrombin, respectively. Activity of single-unit, ischemia-sensitive cardiac spinal afferents was recorded from the left sympathetic chain in anesthetized cats. Injection of 1.5 ml PRP + collagen (activated platelets) into the left atrium (LA) stimulated 12 of 13 cardiac afferents. PRP + saline (nonactivated platelets, LA) and PPP + collagen did not alter activity of these afferents. PRP + thrombin (1.5 ml, LA) stimulated eight of nine other cardiac afferents, whereas PPP + thrombin did not stimulate any of the nine afferents. Antiplatelet immune serum (1 ml/kg iv) significantly decreased circulating platelets as well as neutrophils (polymorphonuclear leukocytes, PMNs) in eight other cats, and in each animal, attenuated the ischemia-related increase in activity of cardiac afferents. Conversely, responses of five separate cardiac afferents to ischemia were not diminished after treatment with anti-PMN immune serum when concentration of circulating platelets was maintained by infusion of donated PRP despite the decrease in circulating PMNs. These data indicate activated platelets stimulate ischemia-sensitive cardiac spinal afferents and contribute to activation of these afferents during ischemia.

Excitatory amino acid receptor antagonist 2APH may improve local CBF during cerebral ischemia in cats.

The present study was designed to investigate in a focal cerebral ischemia model the influence of 2APH, a competitive NMDA receptor antagonist, on the cerebral blood flow of cat cortex, given intravenously before cerebral ischemia. Thirty-four male cats weighing 2.5 to 3.5 kg were anesthetized with halothane and then randomly assigned to either control or experimental group. In the experimented group 18 cats were treated with 2APH and in the control group 16 cats were given saline 10 min before middle cerebral artery occlusion (MCAO). Cortical blood flow (CBF), determined by laser Doppler ultrasound flowmetry, was measured 1 h, 2 h, 3 h, 4 h and 5 h after occlusion. Infarct volume was calculated by summing up the areas in each stained brain section after the experiment. There was a significant difference in the infarct volume of cortex between the 2APH group and the saline control group (P < 0.05). Moreover, we did notice an apparent decrease of the infarct volume in basal ganglia area when 2APH was given (P < 0.01). The total infarct volume was significantly smaller in the group treated with 2APH after MCAO as compared with the saline control group (P < 0.01). The data from the present experiment suggest that NMDA antagonists may not only antagonize the neurotoxic effect of excitatory amino acid on ischemic neuron but also improve the CBF of ischemic brain.

Neuroprotective Effect of Melatonin on Brain Damage Induced by Acute Global Cerebral Ischemia in Cats

Background Melatonin has been proposed as a neuroprotective agent on the basis of its ability to function as a free radical scavenger, provided that lipoperoxidation and other free radical damage induced by reactive oxygen species resulting from cerebral ischemia are relevant pathophysiologic processes of ischemic neuronal damage. Methods The effects of melatonin or vehicle on neurologic deficit scores (Todd scale; maximal deficit score = 100, daily during 7 days after the ischemic episode) and neuronal population of hippocampal CA1–CA4 fields (cresyl violet stain, at the eighth day after the ischemic episode) were evaluated in adult male cats subjected to a 15-min period of acute global cerebral ischemia induced by cardiorespiratory arrest, and in cats subjected to a sham procedure. Continuous intravenous (iv) administration of either melatonin 10 mg/kg/h in 10% ethanol in saline or the vehicle alone (3 mL/kg/h) for 6 h starting 30 min after the end of the period of global cerebral ischemia was used as treatment. Results Global cerebral ischemia resulted in a severe loss of neurons in hippocampal CA1–CA4 fields (9, 13, 30 and 28% remaining neurons, respectively) of ischemic vehicle-treated cats in comparison with sham cats (100%). By contrast, remaining neurons in these regions were between 81 and 100% in the ischemic melatonin-treated cats, values that are nonsignificantly different as compared with sham cats. Values of remaining neurons in CA1–CA4 fields in ischemic melatonin-treated cats were significantly higher than those in ischemic vehicle-treated cats. Neurologic deficit scores in ischemic vehicle-treated cats (42–77 at day 1, 6–39 at day 7) were significantly higher than those in ischemic melatonin-treated cats (16–38 at day 1, 0–6 at day 7) on the days after the ischemic episode. Conclusions Overall, the results support the neuroprotective effect of melatonin against the neuronal cerebral damage induced by acute global cerebral ischemia.

Calcium ion transients in peri-infarct depolarizations may deteriorate ion homeostasis and expand infarction in focal cerebral ischemia in cats.

Harmful effects of peri-infarct depolarizations (PIDs) may depend on recurrent Ca(2+) influx. Thus far, few studies have documented the relevance of PIDs in gyrencephalic animals, and the progressive nature of this process has not been investigated over extended periods. We therefore studied in prolonged focal ischemia in cats spatial and temporal profiles of extracellular calcium ([Ca(2+)](o)) shifts in relation to direct current (DC) potential, nitric oxide (NO) concentration and regional cerebral blood flow alterations, and final pathological outcome. In halothane-anesthetized cats receiving either vehicle (n=12) or MK-801 treatment (5 mg/kg IV; n=10), the left middle cerebral artery was permanently occluded. Laser-Doppler probes, ion-selective microelectrodes, and NO electrodes measured simultaneously regional cerebral blood flow, DC potential, electrocorticogram, [Ca(2+)](o), and NO concentrations in ectosylvian and suprasylvian gyri of the left cerebral cortex. Persistent depolarization immediately after middle cerebral artery occlusion occurred in 10 ectosylvian and 4 suprasylvian gyri of vehicle-treated animals and in 9 ectosylvian and 3 suprasylvian gyri of MK-801-treated animals. PIDs associated with transient decreases of [Ca(2+)](o) were detected in suprasylvian gyri of only 4 vehicle-treated animals, of which 3 developed recurrent PIDs. Electrocorticogram was suppressed during PIDs, and electrocorticogram recovery worsened in a stepwise manner with consecutive depolarizations. PID duration increased slightly with ongoing ischemia and evolved to persistent depolarization at a final stage. NO transients were not detected during PID, and regional cerebral blood flow transients were not pronounced. Infarction was larger with initial persistent depolarization than with PID and was smallest in MK-801-treated animals. PID is not a common finding in peri-infarct zones in cats, and it is suppressed by the N:-methyl-D-aspartate antagonist MK-801. However, if repeated PIDs are generated, they result in a stepwise, progressive breakdown of neuronal function and ion homeostasis, probably contributing to the growth of infarction in focal cerebral ischemia. Recurrent Ca(2+) influx is a mechanism that presumably contributes to this process.

AR-R15896AR reduces cerebral infarction volumes after focal ischemia in cats.

The use of competitive and noncompetitive N-methyl-D-aspartate receptor antagonists to prevent neuronal death during ischemia has been comprehensively studied. This study was performed to examine the neuroprotective effects and pharmacokinetics of the noncompetitive N-methyl-D-aspartate receptor channel blocker (S)-alpha-phenylpyridine-ethanamine dihydrochloride, AR-R15896AR (formerly designated ARL 15896AR), using a gyrencephalic cat middle cerebral artery occlusion model. In a separate experiment, three cats were used for pharmacokinetic analysis, thus establishing the optimal dose of AR-R15896AR. Focal cerebral ischemia was induced in 21 cats. After 30 minutes of a 90-min ischemic insult, the cats received an intravenous infusion (total volume, 3 ml), in a 15-minute period, of either AR-R15896AR or normal saline solution (control). Physiological data were obtained after 40 and 80 minutes of ischemia and at 2, 4, and 6 hours after ischemia. At 6 hours after ischemia, each cat was positioned for both T2- and diffusion-weighted scans (eight slices, 5-mm thick). At 8 hours after ischemia, the animals were perfusion-fixed for histopathological analysis. Pharmacokinetic studies indicated that AR-R15896AR remained in the blood at elevated levels for the 6 hours studied, with a calculated half-life of approximately 6 hours. AR-R15896AR rapidly entered the brain and exhibited a brain/plasma ratio of approximately 8:1. The infarction volumes for the AR-R15896AR-treated group were 1138.5+/-363.1, 651.3+/-428.9, and 118.6+/-50.1 mm3, as calculated using diffusion- and T2-weighted MRI and histopathological data, respectively. The infarction volumes for the control group were 3866.3+/-921, 3536+/-995.7, and 359.9+/-80.2 mm3, as calculated using diffusion- and T2-weighted MRI and histopathological data, respectively. No significant changes were observed in the physiological parameters measured (mean arterial blood pressure, pH, arterial carbon dioxide pressure, arterial oxygen pressure, sodium, potassium, chloride, and glucose levels, hematocrit, and temperature) for either the control or AR-R15896AR-treated group. Postischemic calcium levels returned to normal in the AR-R15896AR-treated cats, whereas they decreased in the control cats. When administered after ischemia, AR-R15896AR was effective in significantly reducing infarction volumes, as measured using diffusion- or T2-weighted magnetic resonance imaging data or quantitative histopathological data. This study also demonstrated that infarction volumes were greater in the diffusion- and T2-weighted magnetic resonance imaging scans than in the qualitative histopathological analyses, with the diffusion-weighted scans exibiting the largest infarction volumes.

Administration of Selective Endothelin Receptor Type a Antagonist Ro 61-1790 Does Not Improve Outcome in Focal Cerebral Ischemia in Cat

The authors examined the effect of selective endothelin (ET) receptor type A (ET(A)) antagonism on histological and functional recovery in cat at 24 hours after reversible middle cerebral artery occlusion (MCAO). A novel and specific ET(A) antagonist, Ro 61-1790 [5-methylpyridine-2-sulfonic acid-6-(2-hydroxyethoxy)-5-(2-methoxyphenoxy)-2-(2-1H-tetrazol-5-y l-pyridin-4-yl)-pyrimidin-4-ylamide sodium salt (1:2)] (Roche, Basel, Switzerland), was used at doses that produced steady-state plasma concentrations and abolished ET-induced pial arteriolar vasoconstriction. In a cranial window preparation, 8 nmol/L ET constricted pial arterioles by 33 +/- 18% (mean +/- SD), but this response was ablated by intravenous Ro 61-1790 treatment (10-mg/kg bolus, 4-mg/kg/h infusion). In additional animal cohorts, halothane-anesthetized cats were treated with 90 minutes of MCAO and 24 hours of reperfusion. Animals received Ro 61-1790 infusion beginning at the onset of reperfusion and continuing for 6 or 24 hours (n = 41). Control cats were treated with 0.9% saline by intravenous infusion throughout reperfusion. There was no difference in injury volume or neurologic evaluation score in saline-treated cats (n = 11; caudate 24 +/- 28%, cortical injury 7.5 +/- 5% of ipsilateral structure; score 52 +/- 8) versus the results in cats treated with Ro 61-1790 for either 24 hours (n = 6; caudate 22 +/- 23%, cortex 6 +/- 5%, injury volume of ipsilateral structure; score 55 +/- 3) or 6 hours (n = 11; caudate 33 +/- 30%, cortex 12 +/- 14%, injury volume of ipsilateral structure; score 50 +/- 10). Mortality was greatest in the 24-hour drug treatment group. These data suggest that blockade of ET(A) receptor activity is not beneficial to tissue or functional outcomes from experimental stroke in cat.

MR Imaging of Experimental Focal Cerebral Ischemia in Cats: Temporal Evolution of Hyperacute Stroke

Purpose : To evaluate the temporal evolution of the ischemic area and trace ratio, and to define ischemic penumbra within the hyperacute experimental focal cerebral ischemia model. Materials and Methods : A focal cerebral ischemia model of middle cerebral artery occlusion (MCAO) was con-structed in twelve Korean cats weighing 2-3 Kg. T2-weighted images (T2WI) and diffusion-weighted images(DWI) were obtained using a 1.5T MR imager. Trace images were reconstructed after post-image processing with IDL 5.0. The trace ratio (ipsilateral trace value/contralateral trace value) was calculated in the ischemic core and periphery, and MR images were obtained at 1, 3, 6, and 24 hrs after MCAO. The twelve cats were di-vided into three groups, and 4, 5, and 3 cats were sacrified after obtaining MR images at 3, 6, and 24 hrs after MCAO, respectively. After 2% triphenyl tetrazolium chloride (TTC) solution and formalin preparation, the in-farction area of the brain slice and T2WI and DWI trace images of the same slice were compared. The trace ratio was calculated at the peripheral portion of the ischemic core, which was the presumed ischemic penumbra in images obtained 1hr after MCAO. Changes in trace ratio in the ischemic core and infarction territory were also evaluated according to time. Results : The trace ratio in the peripheral portion of the ischemic core was 0.710.03. The region where the trace ratio was 0.830.06 in images obtained 1 hour after MCAO was presumed to be ischemic penumbra; the region progressed to infarction in images taken during the next time period. In all cases the abnormal area of trace images was larger than that seen on DWI. The trace ratio was lower, by 6.2 %, 3-6hrs after MCAO than at any other time. In cat number 3, the trace radio decreased rapidly and progressively, by 21%, during the first six hours. For 3-6hrs after MCAO, the area of infarction showed progressive enlargement. Conclusion : Within six hours of MCAO, ischemic penumbra is progressively incorporated into the ischemic core. In the experimental focal cerebral ischemia model, an area of trace ratio larger than 0.71 and less than 1may be defined as ischemic penumbra.

Spinal cord blood flow and pathophysiological changes after transient spinal cord ischemia in cats.

The goal was to study the hemodynamics and regional pathophysiological changes in the spinal cord after transient vascular occlusion in cats. We measured spinal cord blood flow (SCBF) continuously in the lumbar region with a laser-doppler flowmeter, before, during, and after spinal cord ischemia induced by balloon occlusion of the thoracic aorta, in 24 cats (divided into three groups) and simultaneously recorded the evoked spinal cord potentials (ESPs). In each group (n = 8), 10-, 20-, and 30-minute ischemic loading was performed. All animals were evaluated neurologically 36 hours later, and then their spinal cords were examined histologically. The amplitude of ESPs decreased 10 minutes and disappeared 20 minutes after occlusion. SCBF increased to as much as 2 times the control values after reperfusion and decreased gradually in all groups. Then, in all animals in the 10-minute group and six animals in the 20-minute group, SCBF returned to the control values, which were subsequently maintained throughout the experiment, and ESPs returned to normal patterns within 1 hour. For all animals in the 30-minute group and two in the 20-minute group, hypoperfusion after recirculation, irreversible amplitude changes in ESPs, postischemic paraparesis, and pathological ischemic changes in the lower thoracic and lumbar spinal segments were recognized. Our results showed that > 20-minute occlusion of the thoracic aorta in cats resulted in irreversible spinal perfusion disorders and that the monitoring of SCBF and ESPs could be useful for predicting potential neurological deficits. Furthermore, postischemic hypoperfusion may have an important role in the development of secondary spinal cord ischemia, resulting in severe neurological dysfunction. This observation suggested the possibility of therapeutic modification of the secondary processes inducing hypoperfusion after spinal ischemia.

Neither L-arginine nor L-NAME affects neurological outcome after global ischemia in cats.

We attempted to determine whether N-nitro-L-arginine methyl ester (L-NAME) would improve neurological outcome and whether L-arginine (L-ARG) would worsen neurological outcome after transient global ischemia. Halothane-anesthetized cats (n = 6 for each group) were treated with intravenous saline, L-NAME (5 mg/kg or 10 mg/kg), or L-arginine (300 mg/kg) 30 minutes before 10 minutes of ischemia (temporary ligation of the left subclavian and brachiocephalic arteries with hemorrhagic hypotension to 50 mm Hg). At 30 minutes of reperfusion, cats in the L-ARG group were administered an additional 300 mg/kg dose of intravenous L-arginine. Time (mean +/- SE) to isoelectric electroencephalography was similar among groups (saline, 26 +/- 11 seconds; L-NAME-5, 15 +/- 4 seconds; L-NAME-10, 36 +/- 27 seconds; and L-ARG, 22 +/- 7 seconds). At 72 hours, reperfusion pathological injury was severe and neurological deficit score (mean, range) was similar among groups (saline, 38[11 to 70]; L-NAME-5, 52 [40 to 73]; L-NAME-10, 47 [23 to 70]; and L-ARG, 40 [0 to 79]). Nitric oxide is not important in the mechanism of brain injury after global ischemia in cats.

Endothelin-B receptors in cerebral resistance arterioles and their functional significance after focal cerebral ischemia in cats.

In the cerebral circulation, endothelin-A receptor activation mediates marked prolonged vasoconstriction whereas endothelin-B (ETB) receptor activation effects dilation. In contrast to some peripheral vascular beds, ET(B) receptor-induced vasoconstriction has not yet been demonstrated in brain vessels. In this study in chloralose-anesthetized cats, with perivascular microapplications of ET(B) selective agonist (BQ-3020) and antagonist (BQ-788), we investigated whether ET(B) receptor-mediated constriction could be uncovered in cortical arterioles in vivo. In addition, we examined whether normal dilator response to ET(B) receptor activation is preserved in postischemic cerebral arterioles. The first microapplication of the selective ET(B) receptor agonist BQ-3020 (1 micromol/L) onto a pial cortical arteriole elicited marked dilation (caliber increased by 26.3 +/- 15.1% from preinjection baseline). A second application of BQ-3020 (10-minute interval) onto the same vessel failed to evoke any significant vasomotor response. Subsequent (third and fourth) adventitial microapplication of the ET(B) receptor agonist on the same arteriolar site effected a significant constriction of cerebral arterioles (-15.3 +/- 12.7% and -9.7 +/- 6.3% from preinjection baseline, respectively, at 20 and 30 minutes after the first application). The pial arterioles did not display tachyphylaxis to repeated applications of potassium (10 mmol/L). The perivascular application of the ET(B) receptor antagonist BQ-788 (0.001 to 1 micromol/L) had no effect on arteriolar caliber per se but blocked both BQ-3020-induced dilation (inhibitory concentration approximately 5 nmol/L) and vasoconstriction elicited by repeated activation of ET(B) receptors. After middle cerebral artery occlusion, most of the arterioles examined displayed a sustained dilation. The microapplication of BQ-3020 into the perivascular space surrounding postischemic dilated arterioles elicited a constriction of a similar magnitude to that induced by application of CSF (-17 +/- 7% and -17 +/- 7% from preinjection baseline, respectively). The adventitial microapplication of the ET(B) receptor antagonist (BQ-788, 0.1 micromol/L) on postocclusion dilated pial arterioles effected no change in the arteriolar caliber when compared with preinjection baseline. This BQ-788-induced response was significantly different from that induced by perivascular microinjection of CSF (P < 0.001, analysis of variance). These investigations indicate that (1) repeated activation of ET(B) receptors displays tachyphylaxis of the vasodilator response but also uncovers significant constriction of cerebral arterioles in vivo; (2) the ability of BQ-3020 to elicit dilation is lost within 30 minutes of induced focal ischemia; and (3) ET(B)-mediated contractile tone contributes in a small but significant manner in limiting postischemia dilation of cortical pial arterioles.

Inhibition of nitric oxide synthesis accelerates the recovery of polysynaptic reflex potentials after transient spinal cord ischemia in cats.

Nitric Oxide (NO) has been implicated as a mediator of neuronal injury in vascular stroke. On the other hand, NO is suggested to play a neuroprotective role by increasing blood flow during cerebral ischemia. In order to evaluate the role of NO in the spinal cord ischemia, effects of nitric oxide synthase (NOS) inhibition on the recovery of reflex potentials after a transient spinal cord ischemia were examined in urethane-chloralose anesthetized spinal cats. Spinal cord ischemia was produced by occlusion of the thoracic aorta and the both internal mammary arteries for 10 min. Regional blood flow (RBF) in the spinal cord was continuously measured with a laser-Doppler flow meter. The monosynaptic (MSR) and polysynaptic reflex (PSR) potentials elicited by electrical stimulation of the tibial nerve, were recorded from the L7 or S1 ventral root. The recovery process of spinal reflex potentials was reproducible when the oclusion was repeated twice at an interval of 120 min. Pretreatment with N(G)-monomethyl-L-arginine (L-NMMA, 10 mg/kg), a NOS inhibitor significantly accelerated the recovery of PSR potentials after spinal cord ischemia. The accelerating effect of L-NMMA on the recovery of PSR potentials was abolished by co-administration of L-arginine (1 mg/kg/min) but not by that of D-arginine (1 mg/kg/min). L-NMMA failed to improve RBF in the spinal cord during ischemia and reperfusion. Nitroprusside (10 microg/kg/min), a NO donor, retarded the recovery of PSR potentials after spinal cord ischemia. These results suggest that NO production has a significant influence on the functional recovery after transient spinal cord ischemia.

Intravenous basic fibroblast growth factor decreases brain injury resulting from focal ischemia in cats.

We tested the hypothesis that intravenous administration of basic fibroblast growth factor (bFGF) during 4 hours of permanent focal ischemia would affect acute brain injury. Halothane-anesthetized cats underwent left middle cerebral artery (MCA) occlusion for 4 hours. Control cats received diluent (n = 14). Experimental cats were treated with bFGF at a rate of 5 (n = 13), 50 (n = 13), or 250 microg/kg per hour (n = 9) intravenously beginning 60 minutes after initiation of ischemia and continuing until the end of the protocol. As measured by the microsphere method, blood flow to ipsilateral caudate nucleus and ipsilateral inferior temporal cortex was decreased similarly during ischemia, before drug administration, in all groups. Likewise, there was no difference in blood flow to ipsilateral caudate nucleus or inferior temporal cortex as a result of bFGF administration during MCA occlusion. Triphenyltetrazolium-determined injury volume of the ipsilateral cerebral cortex (control, 40+/-7%; bFGF 5 microg/kg per hour, 22+/-5%; bFGF 50 microg/kg per hour, 26+/-7%; bFGF 255 microg/kg per hour, 23+/-6% of ipsilateral cerebral cortex; mean+/-SEM) was less in cats treated with bFGF. There was no difference among groups in injury volume to caudate nucleus (control, 29+/-8%; bFGF 5 microg/kg per hour, 29+/-8%; bFGF 50 microg/kg per hour, 21+/-7%; bFGF 250 microg/kg per hour, 32+/-7% of ipsilateral caudate nucleus). Somatosensory evoked potential amplitude decreased similarly (to <20% of baseline amplitude in all groups) during MCA occlusion and was not altered by bFGF administration. CONCLUSIONS; These data indicate that systemic administration of bFGF ameliorates acute injury in the cerebral cortex without increasing blood flow during focal ischemia in cats. Because bFGF afforded protection when administered after the onset of ischemia, bFGF may provide its beneficial effect by limiting progression of injury in ischemic border regions.

Regional brain polyamine levels in permanent focal cerebral ischemia

Transient global cerebral ischemia has been shown to induce marked changes in the polyamine pathway with a significant increase in putrescine, the product of the ornithine decarboxylase reaction. This study examined the relationship between tissue and extracellular polyamines and regional cerebral blood flow and brain edema. Six hours of focal ischemia in cats ( n = 10) was produced by permanent middle cerebral artery occlusion. Extracellular polyamines were measured in extracellular fluid obtained by microdialysis. Regional cerebral blood flow using laser Doppler flowmetry and specific gravity, an indicator of brain edema, were measured in contralateral (non-ischemic), penumbra and densely ischemic brain regions. A significant increase in the tissue putrescine level was found in the penumbra but there was no difference in the putrescine levels between contralateral and densely ischemic regions. There was no significant change in the spermidine and spermine levels in the three regions. Extracellular levels of putrescine and spermidine were found to be significantly lower than the tissue levels and no change in polyamines was observed in any region. Significant edema formation was observed in densely ischemic and penumbra regions. This is the first demonstration that tissue putrescine is increased in the penumbra region, an area of incomplete ischemia that is developing brain edema.

Hydroxyl radical production during myocardial ischemia and reperfusion in cats.

We previously showed that generation of reactive oxygen species during myocardial ischemia and reperfusion stimulates cardiac sympathetic afferent nerve endings. We hypothesized that, in this feline model of brief ischemia and reperfusion, HO. is produced during ischemia and the rate and concentration of production of HO.during reperfusion is dependent on the duration of myocardial ischemia. Therefore, we evaluated the time dependency of production of HO. during reperfusion after 2, 5, and 10 min of reversible occlusion of the left anterior descending (LAD) coronary artery to induce ischemia in cats (n = 10). Blood samples collected from the coronary vein at 0.25, 1, 2, and 4 min after 2 min of ischemia revealed net cumulative rate of production of p-, m-, and o-tyrosine of 99 +/- 31, 10 +/- 5.1, and 0.8 +/- 0.2 nmol.min-1.g-1, respectively. After 5 min of ischemia, net cumulative rates of production of p-, m-, and o-tyrosine during reperfusion were 177 +/- 63, 74 +/- 26, and 1.6 +/- 0.8 nmol.min-1.g-1, respectively, whereas after 10 min of ischemia production rates were 153 +/- 42, 78 +/- 29, and 2.1 +/- 0.5 nmol.min-1.g-1, respectively. The highest rate of production of tyrosines was observed immediately after ischemia, perhaps indicating a washout of HO.-derived products that had accumulated in the myocardium during ischemia. To evaluate production of HO. during ischemia, deoxygenated saline (PO2 10 +/- 0.9 mmHg) containing phenylalanine was perfused into the ischemic coronary vascular bed through a cannula placed in the LAD (n = 16). Perfusate was collected from the coronary vein during the 10 min of ischemia. Net production of HO. during ischemia, measured by the production of p-, m-, and o-tyrosine, was 82 +/- 11, 6.6 +/- 0.4, and 1.7 +/- 0.3 nmol.min-1.g-1, respectively. Pretreatment with deferoxamine (10 mg/kg, n = 7) or dimethylthiourea (10 mg/kg, n = 6) decreased net production of HO. during ischemia and reperfusion. These results demonstrate that HO. is produced during brief ischemia and reperfusion, with the greatest amount being produced immediately after ischemia. Additionally, we show that the duration of brief ischemia determines the rate of production of HO. during reperfusion.