Rat Embolic Stroke Research Articles

Effect of Delayed Thrombolysis with rt-PA in a Rat Embolic Stroke Model

The effect of delayed thrombolysis with recombinant tissue plasminogen activator was tested in an embolic stroke model. The carotid territory was embolized in 103 rats with fibrin-rich clots formed and washed in polyethylene tubes. Hemispheric cerebral blood flow before and after embolization was measured by the intra arterial 133Xe injection method. At five delay times, 15-240 min after embolization, 69 animals were treated with tissue plasminogen activator, 20 mg/kg, and 34 animals with saline. Carotid angiography displayed the grade of occlusion of the cerebral arterial supply before and after treatment. Brains were fixed after 2 days, evaluated neuropathologically, and infarct volume measured. Cerebral blood flow was reduced by 56-71% after embolization. Reperfusion induced by thrombolytic therapy was demonstrated by comparing the posttreatment angiography of the pooled five treatment groups to control animals. Thrombolytic therapy significantly reduced the infarct volume and improved the prekill clinical score by up to 2 h of treatment delay, and treatment might have been beneficial even after 4 h delay. Prolonging the delay of treatment increased the infarct volume (p < 0.001, Jonck-heere-Terpstra test). Only a few hemorrhagic complications were observed. Thus, thrombolytic therapy in embolic stroke induced recanalization. The effect on clinical outcome and infarct volume was dependent on delay time.

The influence of body temperature on infarct volume and thrombolytic therapy in a rat embolic stroke model

The effect of body temperature on cerebral infarcts and thrombolytic therapy was investigated in 91 rats embolized in the right carotid territory. Hypothermia of 32°C for 2 h with preembolic onset ( n = 15) or hyperthermia of 39°C for 2 h with postembolic onset ( n = 22) was compared to normothermic controls ( n = 17). After 48 h of survival, neuropathological evaluation with measurement of infarct volume was performed. Median infarct volume in percent of affected himisphere volume was 11% (9–21, quartiles) in rats treated with hypothermia alone, compared to 46% (14–59, quartiles) in normothermic controls ( P = 0.04). Hyperthermia for 2 h increased median infarct volume to 65% (37–75, quartiles). There was a positive and significant correlation between infarct volume and body temperature ( R = 0.53, P = 0.0002, n = 54). Mortality rate was significantly higher among rats treated with hyperthermia compared to normothermic controls ( P = 0.005). A subset of 37 rats exposed to the same temperature regimen were treated with tissue plasminogen activator (20 mg/kg i.v. during 45 min) 2 h after embolization. Judged by posttreatment carotid angiography, hyperthermic rats ( n = 11) had the best degree of recanalization ( P = 0.03) compared to controls ( n = 17), but median infarct volume in this group was (58% (27–67, quartiles)) significantly larger ( P < 0.02) than normothermic (21% (15–39, quartiles), n = 14) and hypothermic (13% (7–31, quartiles)), n = 12) rats treated with thrombolytic therapy. Thrombolytic therapy following 2 h of hypothermia, could not improve the effect of hypothermia alone. We conclude, that the size of infarcts in our embolic stroke model is dependent on the body temperature during the initial phase of infarct development. Hyperthermia had a detrimental effect when combined with thrombolytic therapy and should be avoided in clinical trials of this treatment.

Neuroprotection by excitatory amino acid antagonist augments the benefit of thrombolysis in embolic stroke in rats.

The effects of delayed thrombolysis with alteplase and neuroprotection with an excitatory amino acid receptor antagonist and their combination were tested in an embolic stroke model. In 61 rats the carotid artery territory was embolized with arterial-like fibrin-rich clots. Hemispheric cerebral blood flow before and after embolization was measured by intra-arterial 133Xe injection method. The animals were assigned to one of the following treatments: (1) vehicle-treated controls (n = 15); (2) dizocilpine 1 mg/kg i.v. 5 minutes after embolization (n = 16); (3) alteplase 20 mg/kg as an intravenous continuous infusion starting 2 hours after embolization (n = 16); and (4) both agents (n = 14). Carotid angiography displayed the site of occlusion of the cerebral arterial tree immediately after and 3 hours after embolization, and the clinical neurological score was assessed after the rats recovered from anesthesia and before the rats were killed. Brains were fixed after 2 days and evaluated neuropathologically; infarct volume affecting cortical and deep brain structures was measured separately. Both alteplase and dizocilpine reduced the total infarct volume (P = .05 and P = .04, respectively, Mann-Whitney tests). Dizocilpine reduced the incidence of cortical infarctions by 48% (P < .001, Fisher's test). Only the combined treatment significantly reduced deep brain infarctions (P = .03, Mann-Whitney test). The combined treatment also improved the clinical score by 83% compared with controls, by 75% compared with the group treated by dizocilpine alone, and by 50% compared with the group treated by alteplase alone. Sixty-seven percent of thrombolytic-treated animals recanalized completely compared with 39% of those given no thrombolytics (P = .05, Fisher's test). The clinical outcome correlated with infarct size (P < .01, Spearman test). Our results document comparable efficacy of delayed thrombolysis and excitatory amino acid receptor antagonism in this model and suggest that combination of these two therapeutic approaches may yield additional benefit in treatment of thromboembolic stroke, particularly in cases where deep brain (end-artery-supplied) structures are affected.

Enhancing the efficacy of thrombolysis by AMPA receptor blockade with NBQX in a rat embolic stroke model

Efficacy and safety of combined α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor blockade and thrombolytic therapy with human recombinant tissue plasminogen activator (TPA) was tested in a rat embolic stroke model. Sixty-three rats were embolized in the right internal carotid territory with a 200 μl suspension of microclots formed by alternate moving of 150 μl whole blood and 50 μl of thrombin between two interconnected syringes for 4 min. Sixteen embolized rats served as controls, and 16 rats were treated with NBQX immediately after embolization. Thirty-one rats were treated with TPA 2 h following embolization, and in 16 of these rats additional NBQX treatments were initiated 90 min following embolization. Hemispheric cerebral blood flow (CBF) was measured by an intraarterial 133Xenon injection method before and after embolization. Carotid angiography displayed the rate of occlusion of the cerebral arterial supply before and after treatment. Brains were fixed after 2 days, evaluated neuropathologically, and infarct volumes were measured. Median CBF was reduced by 70–77% in the affected hemispheres following embolization. Significant recanalization occurred in all groups except those treated with NBQX. TPA-treated rats had significantly better reperfusion compared to controls judged by angiography 3 h following embolization ( P = 0.04). NBQX alone and TPA alone caused insignificant reduction in infarct volume but, when combined, total infarct volume was reduced by 77% compared to controls ( P = 0.02). Separate measurement of cortical infarct revealed significantly smaller infarcts ( P = 0.05) in the combined treatment group compared to the TPA treatment group. Mortality rate was 19% among controls, 31% among NBQX alone, and 25% among the combined treatment group. Rats treated with TPA alone had a significantly lower mortality rate (0%; P = 0.05, treated vs. controls). The combination of NBQX administered prior to delayed TPA treatment (120 min) significantly reduced cerebral infarct size in rats. The combined therapy was superior to either therapy alone.

Neuroprotection with NBQX and thrombolysis with rt-PA in rat embolic stroke

The efficacy of delayed thrombolysis with recombinant tissue plasminogen activator was tested in combination with the ischaemic protecting drug NBQX in an embolic stroke model. In 113 rats the carotid territory was embolized with a fibrin-rich clot formed in polyethylene tube. Hemispheric cerebral blood flow (CBF) was measured by intra-arterial 133Xenon injection method before and after embolization. Two hours after embolization 67 animals were treated with tissue plasminogen activator 20 mg kg-1, 46 control animals with saline. NBQX was given to 53 animals, of which 41 animals also received thrombolytic therapy and 12 were saline controls. Carotid angiography displayed the rate of occlusion of the cerebral arterial supply before and after treatment. Brains were fixed after two days, evaluated neuropathologically, and infarct volume was measured. Embolization caused a 60-78% reduction of median CBF. The comparison of post-treatment angiography of thrombolytic treated animals to controls showed significant (p < 0.01) reperfusion in thrombolytic treated animals, while NBQX alone did not enhance reperfusion. Thrombolytic therapy significantly reduced the total infarct volume from 19.5% to 4.5% of embolized hemisphere volume (p = 0.006). NBQX alone reduced total infarct volume from 19.5% to 6.5% and cortical infarct volume from 7.9% to 0.3% (p = 0.03). In thrombolytic treated animals NBQX reduced total infarct volume from 4.5% to 2.1%. The more than 50% reduction of total infarction volume caused by NBQX was not statistically significant due to the variation of infarct size in this model. Small haemorrhagic lesions in infarcts were observed in thrombolytic treated animals. The clinical outcome correlated well with infarct volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydroxyethyl starch 200/0.5 reduces infarct volume after embolic stroke in rats.

We evaluated isovolumic hemodilution with hydroxyethyl starch 200/0.5 in a rat model of focal cerebral ischemia. This compound avoids the unfavorable viscosity and erythrocyte aggregation abnormalities of low molecular weight dextran during administration over a period of several days. Sprague-Dawley rats, anesthetized with 0.5-1% halothane and 70% N2O, were subjected to silicon cylinder (treated and control groups) or sham (sham group) embolization of the cerebral circulation. Thirty minutes after embolization, the treated group (n = 5) was infused with 11 ml/kg of 10% hydroxyethyl starch 200/0.5, and the control (n = 5) and sham (n = 4) groups were infused with saline for 1 hour. In the treated group, 7.1 ml/kg of blood was withdrawn. After 24 hours, the animals were reanesthetized, and cerebral blood flow was determined with [14C]iodoantipyrine. Alternative brain slices were either incubated with 2,3,5-triphenyltetrazolium chloride for infarct volume determination or frozen for ischemic volume and cerebral blood flow determination using autoradiography. The hematocrit in the treated group was reduced from (mean +/- SEM) 46 +/- 1% to 35 +/- 2% at 1.5 hours (p < 0.01). Cortical blood flow was within the normal range of 115-185 ml/min/100 g, except for the ischemic cortex in the embolized groups, treated and control. The ischemic and infarct volume of the treated group was reduced by 74% (p < 0.05) and 89% (p < 0.05), respectively, from the control group. The treated and sham ischemic and infarct volumes were not statistically different. These data suggest that hydroxyethyl starch 200/0.5 could be an effective treatment for ischemic stroke when administered early, because it reduces infarct and ischemic volumes from control values to levels indistinguishable from those of the sham group.

Dose-response of rt-PA and its combination with aspirin in a rat embolic stroke model.

The efficacy and safety of thrombolysis with different dose regimens of recombinant tissue plasminogen activator (rt-PA) and its combination with aspirin was tested in an embolic stroke model. In rats the carotid territory was embolized with a single clot formed in a polyethylene tube and washed with saline. Fifteen minutes after embolization 10 animals were treated with rt-PA 10 mg kg-1; 11 with 15 mg kg-1; 12 with 20 mg kg-1 and 9 with 10 mg kg-1 + 20 mg kg-1 aspirin and 34 animals with saline. Rt-PA 10 mg kg-1 reduced median infarct volume (in percent of the ipsilateral hemisphere volume) from 19.5 to 4.8; rt-PA 15 mg kg-1 to 2.0; rt-PA 20 mg kg-1 to 0.0, while rt-PA 10 mg kg-1 + aspirin resulted in a median infarct volume of 9.5%. Thrombolytic therapy significantly and dose dependently (p = 0.001) reduced the infarct volume, improved the presacrifice clinical score and increased (p = 0.02) angiographically verified reperfusion. There was no additional benefit of coadministration of aspirin.

Reduction of infarct volume and mortality by thrombolysis in a rat embolic stroke model.

Thrombolytic therapy with recombinant tissue plasminogen activator was tested in a rat embolic stroke model. The rat carotid territory was embolized with arterial-like microthrombi formed under pressure. Hemispheric cerebral blood flow before and after embolization was measured by the intraarterial Xenon-133 injection method. Fifteen minutes after embolization, 24 rats were treated with 3 mg/kg or 10 mg/kg tissue plasminogen activator, and 27 were treated with saline. Carotid angiography displayed the rate of occlusion of the cerebral arterial supply before and after treatment. Brains were fixed and evaluated neuropathologically and infarct volume was measured. Cerebral blood flow was reduced 70-86% after embolization. The comparison of pretreatment and posttreatment angiography showed significant (p = 0.0005) reperfusion in the treated rats. Thrombolytic therapy significantly reduced the infarct volume from 55.1% to 24.4% of embolized hemisphere volume (p = 0.007) and increased the survival rate from 0.48 to 0.96 (p = 0.0004). Fifty-three percent of the embolized rats recanalized completely after thrombolytic treatment and developed almost no infarction (median volume 2.8%), and all survived. No hemorrhagic complications were observed. Early thrombolytic therapy induced recanalization and reduced mortality and infarct volume after embolic stroke in this model.

EFFECT OF TEMPERATURE ON THE OXYGEN CONSUMPTION OF BRAIN TISSUE

EFFECT OF TEMPERATURE ON THE OXYGEN CONSUMPTION OF BRAIN TISSUE