Canine Model Of Coronary Thrombosis Research Articles

Thrombolytic and anticoagulant effects of a recombinant staphylokinase-hirudin fusion protein

A pure recombinant staphylokinase-hirudin fusion protein (SFH) was obtained by recombinant genetic engineering and purification techniques. The thrombolytic and anticoagulant activities of SFH were investigated using in vitro coagulation models and chromogenic assays. The results showed that intact SFH had targeted thrombolytic activity, and gained anticoagulant activity when cleaved by FXa. In addition, we investigated the pharmacodynamics of SFH in vivo using a variety of animal models, including a rat inferior vena cava thrombosis model, a rat coronary thrombosis model, a rabbit carotid artery thrombosis model and a canine coronary thrombosis model. We found that SFH had an obvious thrombolytic effect and could prevent and reduce re-embolization after thrombolysis and reduce the serious bleeding side effects caused by the combination of thrombolytic and anticoagulant drugs. The results suggest that SFH can be used for thrombolytic therapy in thromboembolic diseases.

Adjunctive treatment with ticagrelor, but not clopidogrel, added to tPA enables sustained coronary artery recanalisation with recovery of myocardium perfusion in a canine coronary thrombosis model

Reperfusion therapy for myocardial infarction is limited by significant re-occlusion rates and less-than-optimal myocardial tissue perfusion. It was the objective of this study to assess and compare the effect of ticagrelor, the first reversibly binding oral P2Y12 receptor antagonist, with that of clopidogrel, in conjunction with thrombolytic therapy, on platelet aggregation, thrombus formation, and myocardial perfusion in a canine model. Thrombus formation was induced by electrolytic injury and blood flow was measured with a Doppler ultrasonic flowmeter. All animals received tissue plasminogen activator (tPA) (1 mg/kg over 20 min); 10 animals received clopidogrel (10 mg/kg IV bolus over 5 min), 10 animals received ticagrelor initiated with a 1-min bolus (75 microg/kg/min), followed by continuous infusion (10 microg/kg/min) for 2 h, and 10 animals received IV saline. Re-occlusion rate and cyclic flow variation decreased with ticagrelor compared to saline groups (p<0.05). Adenosine phosphate (ADP)-induced platelet aggregation decreased with ticagrelor (1.9% +/- 2.67) and clopidogrel (1.11% +/- 2.0) vs. saline (26.3% +/- 23.5, p<0.05) at the end of adjunctive therapy. Bleeding time increased in the clopidogrel compared to the ticagrelor group (p=0.01). Infarct size was reduced with ticagrelor compared to the clopidogrel and saline groups (p<0.05). Blood flow remained significantly below baseline values at 20 min after tPA administration in the saline and clopidogrel groups but not in the ticagrelor group. In conclusion, in a dog coronary thrombosis model, ticagrelor blocks ADP-induced platelet activation and aggregation; prevents platelet-mediated thrombosis; prolongs reperfusion time and reduces re-occlusion and cyclic flow variation; and significantly decreases infarct size and rapidly restores myocardial tissue perfusion.

The von Willebrand factor antagonist (GPG-290) prevents coronary thrombosis without prolongation of bleeding time

The interaction between von Willebrand factor (VWF) and platelet glycoprotein Ibalpha (GPIbalpha) is a critical step that allows platelet adhesion, activation and subsequent thrombus formation to the injured vessel wall under high-shear conditions. In this study, we sought to investigate 1) whether GPG-290, a recombinant human GPIbalpha chimeric protein, would prevent thrombosis in a canine model of coronary thrombosis by blocking VWF-GPIbalpha interaction; and 2) whether desmopressin (DDAVP), a VWF release stimulant, could reduce the prolonged bleeding time caused by a 10x efficacious dose of GPG-290. The antithrombotic efficacy of GPG-290 was evaluated by the in-vivo ability to prevent cyclic flow reductions (CFRs) and ex-vivo inhibition of platelet adhesion/aggregation reflected by prolongation of Platelet Function Analyzer (PFA-100) collagen/ADP closure time. The anti-hemostatic effect was assessed by template bleeding time. GPG-290 at doses of 25, 50 and 100 microg/kg abolished CFRs in 67%, 100% and 100% of the treated dogs without bleeding time prolongation, respectively; GPG-290 dose-dependently prolonged the ex-vivo collagen/ADP-closure time, while it had no effects on plasma VWF antigen level (VWF:Ag) and VWF-collagen binding activity (VWF:CB); the prolonged template bleeding time caused by 500 microg/kg of GPG-290 was prevented by intravenous infusion of DDAVP (0.3 microg/kg). In conclusion, GPG-290 appears to be an effective agent for treating arterial thrombosis without bleeding time prolongation.

Sildenafil Improves Coronary Artery Patency in a Canine Model of Platelet-Mediated Cyclic Coronary Occlusion After Thrombolysis

We sought to assess the effect of sildenafil, a highly-specific type 5 phosphodiesterase (PDE5) inhibitor, on platelet-mediated cyclic coronary flow reductions occurring in a canine model of coronary thrombosis despite aspirin therapy. The PDE5 inhibitors augment the antithrombotic effects of nitric oxide in vitro and in vivo, but it has been proposed that the PDE5 inhibitor sildenafil is prothrombotic. Cyclic coronary flow reductions were induced in the left anterior descending coronary artery by creation of a stenosis, endothelial injury, and thrombus formation followed by treatment with aspirin, heparin, and tissue plasminogen activator. After an initial observation period, dogs were treated with or without sildenafil (100 microg/kg bolus followed by 4 microg/kg/min infusion). Cyclic coronary flow reductions ceased in five of six animals 18 +/- 5 min after initiation of sildenafil but continued in all six control animals. The portion of the observation period during which the coronary artery was patent increased from 52 +/- 9% to 83 +/- 5% after sildenafil administration (p = 0.008) but did not differ between the first and second observation periods in untreated dogs (49 +/- 11% vs. 44 +/- 11%, respectively). Among animals with plasma free sildenafil levels > or =20 nmol/l, cyclic coronary flow reductions were 73 +/- 12% less frequent and the time to cessation of cycling 72 +/- 14% shorter than in animals with levels <20 nmol/l (p < 0.05 for both). Sildenafil transiently decreased blood pressure 7 +/- 1% but did not change heart rate. Sildenafil treatment reduced ex vivo thrombin-induced platelet aggregation by 39 +/- 3% (p < 0.005). Sildenafil improves coronary patency in a canine model of platelet-mediated coronary artery thrombosis, likely via inhibition of platelet aggregation.

Cessation of platelet-mediated cyclic canine coronary occlusion after thrombolysis by combining nitric oxide inhalation with phosphodiesterase-5 inhibition

OBJECTIVESWe sought to evaluate the ability of type 5 phosphodiesterase (PDE5) inhibitors to augment the antithrombotic effects of inhaled nitric oxide (NO) in a canine model of platelet-mediated coronary thrombosis after thrombolysis.BACKGROUNDType 5 phosphodiesterase inhibitors potentiate the ability of NO to inhibit platelet aggregation in vitro by preventing platelet cyclic guanosine monophosphate catabolism. We previously reported that breathing low concentrations of NO gas attenuated, but did not prevent, cyclic flow reductions (CFRs) in a canine model of coronary thrombosis after thrombolysis.METHODSCyclic flow reductions were induced after creation of a left anterior descending coronary artery stenosis, endothelial injury, thrombus formation and thrombolysis. Dogs were either untreated or treated with inhaled NO (20 ppm by volume), intravenous zaprinast, intravenous dipyridamole or the combination of inhaled NO with either PDE5 inhibitor (n = 4 per group).RESULTSCyclic flow reductions ceased, and complete coronary patency was achieved in all dogs after they breathed NO combined with zaprinast (by 12.0 ± 4.7 min [mean ± SEM]) or dipyridamole (by 9.8 ± 4.7 min). The frequency of CFRs was unaffected by NO, dipyridamole or zaprinast alone. Systemic arterial blood pressure and bleeding time were unchanged with any treatment. Ex vivo thrombin-induced platelet aggregation in dogs breathing NO and receiving dipyridamole was reduced by 75 ± 7% (p < 0.05).CONCLUSIONSThe PDE5 inhibitors potentiated the antithrombotic properties of inhaled NO in a canine model of platelet-mediated coronary artery thrombosis after thrombolysis, without prolonging the bleeding time or causing systemic hypotension.

Brief antecedent ischemia enhances recombinant tissue plasminogen activator-induced coronary thrombolysis by adenosine-mediated mechanism.

Clinical studies have implicated preinfarct angina (brief antecedent ischemia/reperfusion [I/R]) as a predictor of more rapid thrombolysis and lower rates of reocclusion. However, the effects of antecedent ischemia on the efficacy of thrombolysis have not been rigorously assessed. Using a canine model of coronary thrombosis, we aimed to (1) reproduce these clinical findings and (2) determine whether release of adenosine (a potent inhibitor of platelet aggregation via stimulation of platelet A(2) receptors) during brief I/R contributes to this improved patency. To address our first objective, we compared the time required to achieve lysis with recombinant tissue plasminogen activator and patency during the first 2 hours after lysis in dogs in which 1-hour thrombotic occlusion was preceded by brief I/R (10-minute coronary occlusion/10-minute reperfusion) versus 20-minute uninterrupted perfusion (controls). Time to lysis was accelerated in the I/R group versus the control group (11+/-1 versus 35+/-6 minutes, P=0.004). In addition, the duration of subsequent reocclusion was reduced (17+/-12 versus 30+/-11 minutes), and the area of the flow-time profile (normalized to baseline flow x 120 minutes) was increased (64+/-12% versus 35+/-7%, P=0.04) in the I/R cohort. The protocol was then repeated, but all dogs were pretreated with the adenosine A(2)/A(1) antagonist CGS 15943 (CGS, 1.5 mg/kg). Time to lysis (38 versus 39 minutes) and subsequent patency were comparable in the CGS+control group versus the CGS+I/R group. Brief antecedent I/R enhances the efficacy of coronary thrombolysis in this canine model, which is due, at least in part, to an adenosine-mediated mechanism.

Local administration of L-703,081 using a composite polymeric stent reduces platelet deposition in canine coronary arteries

We compared the effect on platelet deposition of the glycoprotein IIb/IIIa receptor antagonist L-703,081, administered locally via a drug delivery stent, with that of a standard metal stent in a canine coronary model. There was a significant reduction in platelet deposition using the L-703,081-impregnated stent compared with the bare metal stent. This study demonstrates an alternative route of delivery of GPIIb/IIIa antagonists with potential advantages over systemic administration.

Melagatran, an oral active-site inhibitor of thrombin, prevents or delays formation of electrically induced occlusive thrombus in the canine coronary artery.

Intravenous administration of thrombin inhibitors, such as hirudin, has been shown to decrease the frequency of coronary artery reocclusion after thrombolysis. However, recent findings in large clinical trials in patients with unstable angina and myocardial infarction have failed to demonstrate a sustained antithrombotic effect after cessation of drug treatment. These findings indicate a need for a prolonged antithrombotic regimen, preferably an orally active thrombin inhibitor. To test the hypothesis that a regimen consisting of oral thrombin inhibitor will delay or prevent the formation of occlusive clot, anesthetized dogs were given saline (n = 9) or a single dose of a novel active site low-molecular-weight thrombin inhibitor melagatran by nasogastric tube (1.5 mg/kg, n = 6; 2.5 mg/kg, n = 6), and 15 min later, a potent thrombogenic stimulus in the form of anodal current (100 microA) was applied to the intimal surface of the narrowed left anterior descending coronary artery (LAD). All saline-treated dogs developed stable thrombus, indicated by zero flow at 34 +/- 7 min after initiation of direct current. On the other hand, one of the six dogs given high-dose melagatran did not develop thrombotic occlusion of the LAD during the entire 4 h of observation. Mean time to occlusive thrombus formation in 11 other dogs was prolonged 4-5 times as compared with that in the saline-treated dogs (p < 0.001). Spontaneous thrombolysis was observed in three of 11 dogs after initial clot formation. Overall, the coronary artery was patent for 68% (low dose) and 75% (high dose) of the observation period in melagatran-treated dogs (vs. 14% of observation period in saline-treated dogs). Peak plasma concentration was 0.87 +/- 0.22 microM in dogs given low-dose and 1.38 +/- 0.30 microM in dogs given high-dose melagatran. The activated partial thromboplastin time (aPTT) increased 1.5-fold at peak plasma concentration of melagatran. These observations imply (a) thrombin generation plays a critical role in thrombus formation in narrowed coronary arteries, (b) oral melagatran prevents or delays thrombus formation, whereas the aPTT is only modestly prolonged, and (c) the thrombus formed in the presence of melagatran is prone to spontaneous lysis in this canine model of coronary thrombosis.

Effect of a Mechanical vs a Pharmacologic Increase in Aortic Pressure on Coronary Blood Flow and Thrombolysis Induced by IV Administration of a Thrombolytic Agent

This study was designed to compare the effect of a mechanical vs a pharmacologic increase in BP on coronary artery blood flow and thrombolysis induced by IV administration of recombinant tissue plasminogen activator. We employed a canine model of coronary thrombosis induced by injection of radioactive blood clot in the left anterior descending coronary artery. Subsequently, all dogs underwent phlebotomy to decrease systolic BP to 75 mm Hg and this decreased coronary blood flow by 50%. BP was increased to 130 mm Hg by norepinephrine (NE) infusion or by inflation of a Fogarty catheter placed in the descending aorta. Interventions with NE or with a Fogarty balloon catheter increased coronary artery blood flow to similar values and rates of coronary thrombolysis were similar. However, cardiac output was significantly higher with NE. These results indicate coronary clot lysis is dependent on perfusion pressure and coronary blood flow, not cardiac output.

Endothelin-1 production in coronary circulation in a new canine model of coronary thrombosis

The purpose of this study was to investigate whether endogenous endothelin-1 (ET-1) production in coronary circulation is associated with acute coronary thrombotic events in vivo. To achieve this goal, we have designed a new experimental canine model of coronary thrombosis. In vivo occlusive thrombus was induced by the intracoronary application of radiofrequency energy (660 kHz, 50 W) in closed-chest dogs. Pathological and immunohistochemical examinations of thrombosed coronary artery were performed. In 12 dogs, plasminogen activator was administered intravenously and serial measurements of ET-1, thromboxane B2 (TXB2) and thrombin-antithrombin III complex (TAT) levels in plasma from the coronary sinus, aortic root and inferior vena cava were examined. Occlusive platelet-rich thrombi were attached to the deeply injured intimal surface. TAT and TXB2 increased rapidly soon after the intimal injury and declined after successful thrombolysis. In contrast, ET-1 in the coronary sinus was elevated after reperfusion and was significantly higher than in the aorta. Net ET-1 production in the coronary circulation showed a significant positive correlation with the peak TAT levels (r = 0.69, P < 0.05), but not with TXB2 or total occlusion time as an index of ischemic severity. Deep intimal injury leads to occlusive coronary thrombus. Thrombus formation and its subsequent lysis is associated with the activation and deactivation, respectively, of the coagulation cascade and platelets. Thrombin generation may stimulate ET-1 production in the coronary endothelium in acute coronary thrombotic events.

Endothelin-1 production in coronary circulation in a new canine model of coronary thrombosis

Endothelin-1 production in coronary circulation in a new canine model of coronary thrombosis

Myocardial contrast echocardiography: relation of collateral perfusion to extent of injury and severity of contractile dysfunction in a canine model of coronary thrombosis and reperfusion

Objectives. This study sought to determine whether myocardial contrast echocardiography could be used to detect and quantitate collateral blood flow capable of limiting the effects of ischemia in an experimental model of coronary thrombosis and reperfusion.Background. Myocardial contrast echocardiography has been used to assess collateral blood flow in humans, but this technique has not been extensively validated in the experimental laboratory.Methods. Myocardial ischemia occurred after electrically induced left circumflex coronary artery thrombosis in a canine model. Ischemia was intensified by administration of vasodilators. Reperfusion was induced with recombinant tissue-type plasminogen activator. Myocardial perfusion was assessed with contrast echocardiography and radiolabeled microspheres. Infarct size was determined by histochemical staining methods. Myocardial samples were evaluated histologically.Results. The dogs were classified into two groups on the basis of contrast echocardiographic detection of perfusion in the ischemic region: those with (n = 13) and without collateral flow (n = 10). Collateral perfusion detected by contrast echocardiography paralleled changes detected by radiolabeled microspheres during thrombosis and vasodilator administration. A 91% agreement was observed between the two techniques in detecting collateral flow >0.3 mi/min per g (p < 0.0001). Collateral perfusion correlated directly with radial shortening fractions of the ischemic myocardium (p < 0.01). Recovery of function after reperfusion was faster, infarct size was smaller (mean [±SD] 4 ± 1% vs. 11 ± 3%, p = 0.05), and histopathologic injury was less in dogs with than without collateral flow, respectively (p < 0.05).Conclusions. Myocardial contrast echocardiography can identify physiologically significant collateral vessels capable of limiting the degree of ischemic damage during coronary thrombosis. The magnitude of collateral flow and the change in flow induced by vasodilators can be assessed and compares favorably with the microsphere standard.

An increase in low aortic pressure increases coronary artery flow and coronary thrombolysis induced by intravenous administrarion of recombinant tissue plasminogen activator

Purpose: Our study investigated the effects of an increase in aortic pressure, induced by norepinephrine (NE) administration on coronary artery flow in a clotted artery, and rate of coronary thrombolysis induced by intravenous (IV) administration of recombinant tissue plasminogen activator (rtPA). Methods: A canine model of coronary thrombosis, induced by intracoronary injection of radioactive autologous blood clots, was used to test the hypothesis that an increase in aortic blood pressure will increase coronary artery flow and the rate of clot lysis induced by IV administration of rtPA. Results: After clot injection, 11 dogs were phlebotomized to decrease systolic aortic pressure to 75 mm Hg. Subsequently, .25 mg/kg of rtPA was administered intravenously over two 15-minute intervals, one during hypotension, and the other after NE infusion had increased systolic blood pressure to 130 mm Hg. In six dogs the hypotensive condition was studied first, and in five dogs the NE-induced normotensive condition was studied first. In all dogs, coronary artery flow and the rate of clot lysis were significantly increased in the normotensive condition. Conclusions: These results indicate that an increase in a low coronary artery perfusion pressure may enhance coronary artery flow and the rate of thrombolysis.

Opposing effects of plasma epinephrine and norepinephrine on coronary thrombosis in vivo.

It is well known that plasma catecholamines and myocardial infarction have a close relation and that coronary artery thrombosis is a major cause of myocardial infarction. In addition, epinephrine is known to be a prothrombogenic agent in vivo. However, the role of the other major circulating catecholamine, norepinephrine, in the development of coronary thrombosis is somewhat uncertain, although the role of norepinephrine is often considered analogous to the role of epinephrine. Therefore, the present study was designed to investigate the effect of norepinephrine and its interaction with epinephrine on coronary thrombosis. To compare the effects of epinephrine and norepinephrine on coronary thrombosis, we analyzed the frequency of cyclic blood flow reductions (CFRs) in an anesthetized canine model of coronary thrombosis (n = 25). Three experiments were used in the present study. In the first experiment with epinephrine infusion, plasma epinephrine was elevated from 0.46 +/- 0.25 to 27.7 +/- 1.85 nmol/L. The frequency of CFRs increased by more than 60%, from 7.1 +/- 0.5 to 11.5 +/- 0.7 in 40 minutes (P < .01). The second experiment included three experimental periods: control, norepinephrine infusion, and norepinephrine infusion plus epinephrine infusion. Norepinephrine was infused to raise plasma norepinephrine from 1.3 +/- 0.2 to 32.4 +/- 4.3 nmol/L. The frequency of CFRs in the dogs was markedly reduced, from 7.89 +/- 0.42 to 2.41 +/- 1.08 in 40 minutes (P < .01), whereas arterial pressure was elevated from 88 +/- 3 to 118 +/- 5 mm Hg (P < .01). However, when epinephrine infusion was added to the norepinephrine infusion, the frequency of CFRs increased from 2.41 +/- 1.08 to 7.74 +/- 1.12 in 40 minutes (P < .01). In the third experiment, a servocontrol device was used during the norepinephrine infusion to prevent rises in coronary arterial pressure. As a result of the norepinephrine infusion, the frequency of CFRs was reduced from 7.47 +/- 0.71 to 0.83 +/- 0.65 in 40 minutes (P < .01), even though the coronary arterial pressure was not altered. The present study demonstrated that infusion of epinephrine stimulated coronary artery thrombosis, whereas infusion of norepinephrine inhibited coronary artery thrombosis. In addition, the inhibitory effect of norepinephrine on coronary thrombosis is independent of increases in coronary arterial pressure. Therefore, the present findings suggest that epinephrine and norepinephrine have opposing effects on coronary thrombosis in dogs.

The New Nitroderivative ITF 296 Improves Collateral Blood Flow in a Canine Model of Coronary Thrombosis

The actions of ITF 296 and isosorbide dinitrate (ISDN), 20, 70, and 200 g/kg/min, on myocardial transmural blood flow distribution during acute thrombotic occlusion of the left circumflex coronary artery (LCX) have been evaluated in seven and three anesthetized open-chest dogs, respectively, and compared with four animals receiving vehicle. Occlusion of LCX was achieved in 14 +/- 2 min by the insertion of a copper coil. This caused transmural myocardial ischemia in the LCX area, while leaving blood flow in the left anterior descending coronary artery (control area) unaffected. Infusion of ITF 296 (200 g/kg/min) increased transmural coronary flow in the border zone and in the control area without affecting blood flow in the central ischemic area. ISDN, given in the same dose, reduced systemic blood pressure but did not affect LCX blood flow. In three dogs with residual perfusion in the LCX central area ITF 296 also increased blood flow. These results confirm that ITF 296 promotes an increase of flow to the border zone, thus possibly reducing the area of myocardial infarction.

The New Nitroderivative ITF 296 Improves Collateral Blood Flow in a Canine Model of Coronary Thrombosis

Journal of Cardiovascular Pharmacology™ is a peer reviewed, multidisciplinary journal that publishes original articles and pertinent review articles on basic and clinical aspects of cardiovascular pharmacology. Appropriate subjects include new drug development and evaluation, physiological and pharmacological bases of drug action, metabolism, drug interactions and side effects, clinical results with new and established agents and novel methods. The focus is on pharmacology in its broadest applications, incorporating not only traditional approaches, but new approaches to the development of pharmacological agents and the prevention and treatment of cardiovascular diseases.

Interaction between plasma potassium and epinephrine in coronary thrombosis in dogs.

Both plasma potassium ([K]) and epinephrine concentrations have been known to increase during exercise and decrease rapidly shortly after exercise; in addition, it is also known that exercise can promote coronary thrombosis in human and animal subjects. Many studies have shown that epinephrine has a stimulatory effect on coronary thrombosis; however, little information is available concerning the effect of raising plasma [K] on coronary thrombosis. The present study was designed to investigate the effect of raising plasma [K] and its interaction with epinephrine infusion on coronary thrombosis. A canine model of coronary thrombosis was used, and the frequency of cyclic blood flow reductions (CFRs) resulting from thrombus formation in the circumflex artery was analyzed in the study. By acutely raising plasma [K] to approximately 6.0 mEq/L, the frequency of CFRs was reduced from 8.0 +/- 0.6 to 3.7 +/- 1.0 in 40 minutes (P < .01). Epinephrine infusion (0.5 microgram.kg-1 x min-1) stimulated the frequency of CFRs from 7.1 +/- 0.5 to 11.5 +/- 0.7 in 40 minutes (P < .01). However, if plasma [K] was raised to approximately 6.0 mEq/L while the epinephrine infusion was continued, the frequency fell from 11.5 +/- 0.7 to 7.7 +/- 1.1 in 40 minutes (P < .01). The present study demonstrated that acutely raising plasma [K] inhibited coronary thrombosis in dogs and also blocked the potentiating effect of epinephrine on coronary thrombosis. These findings may suggest that raising plasma [K] exerts a protective effect against coronary thrombosis and that a rapid decrease in plasma [K], such as that occurring shortly after exercise, facilitates coronary artery thrombosis when the artery has a preexisting pathological condition.

Influence of heparin and systemic lysis on coronary blood flow after reperfusion induced by the novel recombinant plasminogen activator BM 06.022 in a canine model of coronary thrombosis

Objectives. We sought to evaluate whether anticoagulation by an intravenous heparin infusion prevents deterioration of coronary blood flow restored by the novel recombinant plasminogen activator BM 06.022, and to compare the effects of profound fibrinogenolysis with those of an intravenous bolus injection of heparinBackground. Recent clinical studies indicate that heparin appears to be effective in reducing reocclusion when combined with recombinant tissue-type plasminogen activator (rt-PA), but that heparin is associated with an increased bleeding incidence. Therefore, the need for heparin has to be critically evaluated in the development of BM 06.022.Methods. BM 06.022 is an unglycosylated variant of human tissue-type plasminogen activator. Thrombus formation in anesthetized open chest dogs was induced by electrical injury. Left circumflex coronary artery blood flow was monitored for 4 h using an electromagnetic flow probe. Twenty dogs were randomized to receive intravenous heparin (100 IU/kg bolus plus 100 IU/kg per h) in group B or saline solution in group A before an intravenous bolus injection of 200 KU/kg (=0.34 mg/kg) BM 06.022 1 h after thrombus formation. Another 14 dogs were randomized to receive a single intravenous bolus injection of 200 IU/kg heparin plus 200 kU/kg BM 06.022 in group D or saline solution plus 1,000 kU/kg BM 06.022 in group C.Results. In the absence of a systemic lytic state, heparin infusion prolonged (p < 0.05) the cumulative patency time (sum of time intervals during which the coronary artery was patent) to 204.3 ± 7.4 min (group B) compared with 34.6 ± 10.8 min with saline solution (group A), and increased (p < 0.05) the area under the curve for coronary blood flow versus time (AUCFlow) to 34.0 ± 3.4 ml · h · min−1compared with 7.7 ± 4.6 ml · h · min−1. Profound fibrinogenolysis after administration of 1,000 kU/kg BM 06.022 (group C) and a single intravenous heparin injection (group D) did not differ in their effects on the cumulative patency time (182 ± 30.3 vs. 177.5 ± 25.4 min) and AUCFlow(36.0 ± 10.3 vs. 30.5 ± 4.8 ml · h · min−1), but these values were improved (p < 0.05) compared with those obtained after administration of saline solution plus 200 kU/kg BM 06.022 (group A).Conclusions. In the absence of a systemic lytic state, intravenous heparin is required as an adjunct to BM 06.022 to maintain coronary blood flow in dogs.

Beneficial effects of combined thromboxane synthase inhibition/receptor blockade with CGS 22652 in a canine model of coronary thrombosis

Various antiplatelet agents were examined for their effectiveness as adjuncts to thrombolytic therapy in a canine model of thrombin-induced coronary thrombosis. Aspirin (5 mg/kg i.v. bolus), CGS 15435A (thromboxane synthase inhibitor (TxSI), 0.1 mg/kg i.v. bolus + 0.04 mg/kg per h) and BM 13.505 (thromboxane receptor antagonist (TxRA), 0.5 mg/kg i.v. bolus + 0.2 mg/kg per h) administered concurrently with streptokinase (750 000 units/h) were examined for their effects on reperfusion and reocclusion, as were a combination therapy with CGS 15435A + BM 13.505 or the dual TxRA/TxSI inhibitor, CGS 22652 (1 mg/kg i.v. bolus + 0.4 mg/kg per h). All dogs received heparin (150 U/kg bolus + 50 U/kg per h) throughout the experimental protocol. Survival analysis at reperfusion indicated that thrombolysis was significantly improved in dogs treated with CGS 15435A, BM 13.505, CGS 15435A + BM 13.505 or CGS 22652 over that of vehicle-treated animals. Both dual inhibitor groups and the BM 13.505 group were significantly different from aspirin. Aspirin-treated dogs were not different from vehicle. Otherwise, all treatments differed from the vehicle-treated group at reocclusion. Time and incidence of reocclusion for CGS 22652 was significantly improved over that of BM 13.505. Residual thrombus weight was significantly reduced in the CGS 22652-treated and BM 13.505 + CGS 15435A-treated animals. These findings demonstrate that streptokinase-induced thrombolysis is accompanied by TxA 2/prostaglandin H 2 synthesis and platelet activation and suggest a role for platelet activation during reocclusion following clot lysis. These studies also show it is possible to combine the beneficial effects of both a TxRA and TxSI into a single chemical entity, CGS 22652, which, when administered as adjunctive therapy to streptokinase, results in an apparent synergistic antithrombotic effect.

Comparison of hirudin and heparin as adjuncts to streptokinase thrombolysis in a canine model of coronary thrombosis.

Recombinant desulfatohirudin (HI), a potent and specific thrombin inhibitor, was compared with heparin (HE) as an adjunct to streptokinase thrombolysis. In pentobarbital-anesthetized dogs, an occlusive thrombus (whole blood+thrombin) was introduced into the left anterior descending coronary artery (LAD) with superimposed endothelial damage and distal high-grade stenosis. Intravenous infusion of saline (vehicle), HI (0.3 mg/kg followed by 0.3 mg/kg per hour, 1 mg/kg followed by 1 mg/kg per hour, or 2 mg/kg followed by 2 mg/kg per hour), or HE (60 units/kg followed by 40 units/kg per hour or 100 units/kg followed by 60 units/kg per hour) was initiated 15 minutes before streptokinase (750,000 units for 60 minutes) administration. Vessel patency was monitored for 180 minutes after streptokinase administration with a volume flow probe on the proximal LAD. In dogs treated with no adjunctive agent (saline control), none of the vessels were recanalized with streptokinase. Both HI and HE promoted reperfusion, inhibited reocclusion, and reduced the residual thrombus mass in a dose-dependent fashion. However, at comparable levels of therapeutic anticoagulation (activated partial thromboplastin time [APTT] = 1.5-2.0 times baseline) HI exhibited a higher incidence of reperfusion (eight of eight dogs [100%] versus one of eight dogs [12%]), a shorter time to reperfusion (33 +/- 6 versus 59 minutes), a longer duration of initial reperfusion (106 +/- 21 versus 10 minutes), and a smaller residual thrombus mass than did HE. Likewise, the slope of the relation between the APTT prolongation and the total reperfusion time ("anticoagulation/antithrombosis profile") was almost five times higher for the combined HI data than for the HE data. Our results indicate that HI is more effective than HE in enhancing and sustaining coronary recanalization with streptokinase at a HI dose that modestly prolongs coagulation time and does not alter bleeding times.