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.

A rat model of reproducible cerebral infarction using thrombotic blood clot emboli.

The purpose of this study was the development of a model of embolic stroke with high reproducibility concerning infarct volume. In 37 male Sprague-Dawley rats, the internal carotid artery was embolized with in vitro preformed suspensions of autologous microemboli resembling arterial thrombi. With a method of continuous flow through the carotid arterial catheter, reflux of blood with uncontrolled clotting and embolization was avoided, thereby providing control animals free of ischemic damage. The embolized animals had arterial occlusions on angiograms immediately after embolization and no spontaneous recanalization on angiograms 2 h later. The cerebral blood flow measured by the intra-arterial 133Xe injection method decreased to 21-37% of baseline values. All embolized animals developed hemiparesis with spontaneous circling behavior, embolization with more than 150 microliters clot suspension resulted in hemispherical infarcts. There was a strong statistically significant correlation between amount of emboli, rate of vascular occlusion, and volume of infarcted tissue. This is the first model presented utilizing autologous in vitro microemboli imitating "white" arterial thrombi. The animals developed infarction, resembling human stroke.

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.

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

Efficacy and safety of combined alpha-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 microliters suspension of microclots formed by alternate moving of 150 microliters whole blood and 50 microliters 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.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

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

BACKGROUND AND PURPOSE: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

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

BACKGROUND AND PURPOSE: Thrombolytic therapy with recombinant tissue plasminogen activator was tested in a rat embolic stroke model. METHODS: 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. RESULTS: 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. CONCLUSIONS: Early thrombolytic therapy induced recanalization and reduced mortality and infarct volume after embolic stroke in this model.

Reduction of infarct volume by thrombolysis with rt-PA in an embolic rat stroke model.

Thrombolytic therapy with recombinant tissue plasminogen activator was tested in an embolic stroke model. In rats the internal carotid territory was embolized through the internal carotid artery with 50 microliters thrombin-rich (n = 18), 50 microliters thrombin-poor (n = 17) and 20 microliters thrombin poor (n = 13) suspension of arterial-like microthrombi formed under pressure. Hemispheric cerebral blood flow before and after embolization was measured by intra-arterial 133Xe injection method. Fifteen minutes after embolization 19 animals were treated with tissue plasminogen activator 20 mg kg-1, and 22 animals with saline. Carotid angiography displayed the degree of occlusion of the cerebral arterial supply before and after treatment. Brains were evaluated neuropathologically and infarct volume measured. Cerebral blood flow was reduced 72% after embolization with 50 microliters emboli suspension and 32% after embolization with 20 microliters suspension. The comparison of pre- and post-treatment angiography showed some recanalization in the treated animals, control animals had no recanalization. Thrombolytic therapy reduced the infarct volume from 72.8% to 20.9% of embolized hemisphere volume (p = 0.0037) in the 50-microliters thrombin rich-embolized group, from 22.9 to 9.0 (NS) in the 50-microliters-thrombin-poor-embolized group and from 6.6 to 0.0 (NS) in the 20-microliters-embolized group. One third of treated animals recanalized completely and developed smaller (p = 0.03) infarcts than the non-recanalized. No hemorrhagic complications were observed. Early thrombolytic therapy reduced infarct volume after embolic stroke in this model, this effect was dependent upon recanalization.