Experimental Coronary Thrombosis Research Articles

Inhibition of platelet activity in vivo by amlodipine alone and combined with aspirin

Platelets are known to contribute to the initiation and progression of coronary artery narrowing by atherosclerotic plaques. Platelets also initiate periodic occlusive coronary arterial thrombosis that leads to unstable angina and myocardial infarction. Aspirin is the most widely used platelet inhibitor. However, if blood levels of epinephrine are elevated, some of the platelet inhibition produced by aspirin is diminished. Amlodipine, a second generation dihydropyridine calcium channel blocker, was studied in a widely used dog model of experimental coronary artery thrombosis. Amlodipine 1 mg/kg alone or amlodipine 0.4 mg/kg with 5 mg/kg of aspirin IV completely abolished the experimental coronary thrombosis and prevented the exacerbation of coronary thrombosis by epinephrine 0.2 μg/kg/min. This protective effect did not appear until 60 minutes after the amlodipine was given, suggesting a delayed onset of action. Long-acting dihydropyridine calcium channel blockers are used in patients with hypertension, angina, and coronary artery disease. They also may offer the patient some protection against fatal or nonfatal myocardial infarction via their platelet-inhibiting effects.

Human Platelet Ca 2+ Mobilization, Glycoprotein IIb/IIIa Activation, and Experimental Coronary Thrombosis In Vivo in Dogs Are All Inhibited by the Inotropic Agent Amrinone

Inotropic drugs are often used to treat acute, severe heart failure resulting from acute myocardial infarction and other unstable coronary artery syndromes. However, catecholamine inotropic agents may potentiate coronary thrombosis via a platelet alpha2-adrenergic mechanism, thus exacerbating the original problem. The present studies were designed to determine whether the nonadrenergic inotropic and vasodilator drug amrinone, which elevates platelet cAMP levels, would both inhibit human platelet Ca2+ mobilization and adhesion molecule expression ex vivo and protect against experimental coronary thrombosis in vivo in dogs. Human platelets in suspension were preincubated with amrinone 2.5 to 15 microg/mL; stimulated with the agonists thrombin 0.1 U/mL, ADP 10(-6) mol/L, or arginine vasopressin 10(7) mol/L; and studied for Ca2+ mobilization, glycoprotein IIb/IIIa activation, and P-selectin expression by fluorescent flow cytometry methods. Experimental coronary thrombosis in vivo was studied in an open-chest dog model with critical coronary artery stenosis and deep vessel wall injury. Results showed that at the cellular level, amrinone inhibited agonist-induced Ca2+ mobilization and had modest inhibitory effects on adhesion molecule expression. In vivo in dogs, intravenous amrinone 2 mg/kg plus infusion at 20 microg x kg(1) x min(-1) completely abolished coronary thrombosis. The fact that amrinone inhibited human platelet activation at the cellular level and protected against experimental coronary thrombosis in vivo in dogs suggests a potentially advantageous antithrombotic action for this inotropic and vasodilator drug.

High-dose droperidol protects against experimental coronary thrombosis in dogs and pigs and attenuates aggregation of porcine platelets and Ca2+ mobilization in human platelets.

Activation of platelets after contact with thrombogenic substrates may be an early factor leading to coronary artery thrombosis and myocardial infarction. Haloperidol, a butyrophenone, possesses weak in vitro platelet inhibitory activity. Experiments were designed to determine whether droperidol, a butyrophenone adjunct to anesthesia, protected against experimental coronary thrombosis in intravenously anesthetized open-chest dogs and pigs, attenuated ex vivo porcine platelet aggregation, and inhibited agonist-induced increases in [Ca2+]i in human platelets. In dogs and pigs, a lesion consisting of deendothelialization, deep vessel wall injury, and critical stenosis was created in the proximal circumflex arteries, resulting in coronary thrombus formation accompanied by decreased circumflex artery blood flow. Embolization of the thrombus restored flow, but the cycle then repeated, resulting in repetitive cyclical flow reductions (CFRs). These were measured using an electromagnetic flow probe. In dogs, droperidol 0.2 mg/kg intravenous rapidly abolished CFRs in all ten animals, with frequency decreasing from 0.22 +/- 0.01 cycles/min to 0. Droperidol 0.8 mg/kg intravenous rapidly abolished CFRs in seven of eight pigs, with frequency decreasing from 0.15 +/- 0.01 to 0.02 cycles/min (P < 0.005). In both species, additional doses of droperidol were effective against CFRs augmented with intravenous epinephrine, a catecholamine that stimulates thrombosis. Ex vivo platelet aggregation studies were performed in platelet-rich plasma obtained from pigs before and after droperidol 0.8 mg/kg intravenous. Pretreatment with the drug resulted in marked inhibition of aggregation evoked by collagen, modest attenuation of that elicited by adenosine diphosphate (ADP), but no effect on that evoked by arachidonic acid. In human platelets, apparent [Ca2+]i was estimated using the fluorescent indicator indo-1 and flow cytometry. Droperidol 10(-7), 10(-6), and 10(-5)M had a dose-dependent inhibitory effect on the amplitude of increases in [Ca2+]i evoked by 10(-5)M serotonin (plus 10(-7)M epinephrine). The higher droperidol concentration decreased the response to as much as 30% of control (P < 0.001). Droperidol lacked effect on Ca2+ mobilization elicited with 10(-6)M ADP. The results from three experimental models indicate that droperidol attenuates experimental coronary thrombosis in animals and suggest that this inhibition may result, in part, from a direct droperidol depressant effect on platelet activation and aggregation.

Utrastructural analysis of thrombolysis by streptokinase and tissue-type plasminogen activator of experimental coronary arterial thrombosis

Thrombolysis was studied in dog coronary arteries after reperfusion by i.v. streptokinase or tissue plasminogen activator (t-PA). A thrombus was formed with whole blood and thrombin in the left anterior descending coronary artery of anesthetised, open-chest dogs. Reperfusion was monitored by electromagnetic flow probe. Arteries from sham-operated dogs (no occlusive thrombi) and from saline, streptokinase and t-PA-infused dogs (collected at the time of reperfusion or 40 min after reperfusion) were examined by scanning electron microscopy. The thrombus in saline-infused dogs was composed of closely packed red blood cells (rbc) and areas rich in fibrin and platelets. Arteries collected from streptokinase- and t-PA-infused dogs at reperfusion showed that flow returned through irregular channels that meander over and delve through the clot. Reperfusion channels were not seen in saline-infused dogs. Despite return of blood flow to control levels, a portion of the thrombus remained in the lumen of the artery in both streptokinase- and t-PA-infused dogs. Deposition of rbc, platelets and fibrin occurred on the surface of the residual thrombus and the adjacent arterial endothelium. These findings indicate that partially occlusive thrombi can remain after successful thrombolysis and may serve as substrata for further deposition of fibrin and platelets.

The Thrombolytic Effects of Native Tissue-Type Plasminogen Activator (AK-124) on Experimental Canine Coronary Thrombosis

To evaluate the thrombolytic effects of the native tissue-type plasminogen activator (t-PA), the authors used a thrombus model simulating clinical situations. The native t-PA (AK-124) was obtained from human-derived normal cells. Experimental canine coronary thrombosis was produced by partial constriction and endothelial denudation of the vessel. In 19 dogs, coronary occlusive thrombus was produced. Three hours after total occlusion of the coronary artery with thrombus, the authors attempted the thrombolytic therapy in 16 dogs. Histologically, three-hour thrombus was composed of a mixture of platelet aggregates, fibrin, and blood cells. They infused 0.375 mg/kg t-PA intravenously in 7 dogs and 20,000 IU/kg urokinase (UK) in 9. Coronary recanalization was achieved in 5 (71%) with t-PA infusion and 6 (67%) with UK infusion. Plasma fibrinogen levels decreased to 76% of preinfusion value in the dogs with t-PA infusion and to 34% in those with UK infusion. Coronary reocclusion occurred in 2 dogs with t-PA and 3 with UK. Thus, the native t-PA (AK-124) can provide coronary thrombolysis without severe depletion of plasma fibrinogen levels.

Preventive effects of batroxobin on experimental canine coronary thrombosis.

The thrombolytic effects of urokinase (UK) and preventive effects of batroxobin, heparin, and aspirin on the recurrence of thrombosis in the coronary artery were studied in 118 anesthetized dogs with severe endothelial denudation and luminal stenosis of the coronary artery. Occlusive thrombi developed in 68 (58%) preparations (dogs), accompanied by a decrease of coronary blood flow and pressure, an electrocardiographic ST elevation, and epicardial cyanosis. An intravenous infusion of 20,000 IU/kg of UK reopened the occluded coronary artery in all 32 preparations with 1-h-old thrombi, in 6 (86%) of 7 preparations with 2-h-old thrombi, and in 5 (83%) of 6 preparations with 3-h-old thrombi. However, recanalization was not observed in preparations with thrombi more than 4-h-old. Occlusion recurred within 6 h after recanalization in 2 (18%) of 18 preparations pretreated with batroxobin (1-2 BU/kg) (p less than .005 vs. control UK group), in 1 (14%) of 7 preparations administered a continuous infusion of 30 U/kg per h of heparin (p less than .05 vs. control UK group), in 4 (57%) of 7 preparations pretreated with 2 mg/kg of aspirin, and in 7 (64%) of 11 preparations not pretreated (control UK group). Complete prevention was observed only in the group administered 2 BU/kg of batroxobin. Histologically, these thrombi closely simulated clinical arterial thrombi. Myocardial hemorrhage and contraction band necrosis were observed in the reperfused hearts. In conclusion, experimental canine coronary thrombi more than 4-h-old were resistant to thrombolytic therapy, and batroxobin and heparin were effective in the prevention of coronary reocclusion.

Histamine release during an experimental coronary thrombosis in awake dog

Histamine is released into the systemic circulation during anaphylaxis, by drugs and surgical procedures. Studies in animal models have shown that released histamine is one of the major mediators of arrhythmia occurring during anaphylaxis or the administration of histamine-releasing drugs. The variations in plasma histamine levels in dogs with a subacute coronary thrombosis were investigated and the effects of dimaprit and cimetidine on the electrocardiographic consequence of this thrombosis and on histamine release were assessed. During the first day after the myocardial infarction a ventricular arrhythmia developed and plasma histamine levels were found significantly increased, returning to the basal values when the sinusal rhythm was restored. Dimaprit was able to decrease the number of ventricular extrasystoles and to modulate plasma histamine levels. The action of dimaprit on ECG was not reversed by pretreatment with cimetidine, which on the contrary was able to antagonize the decrease in plasma histamine concentrations induced by dimaprit perfusion.

Influence of alpha-adrenergic blockade on platelet-mediated thrombosis in stenosed canine coronary arteries.

The functional significance of platelet alpha-adrenergic receptors in vivo is uncertain. The aim of this study was to elucidate their role in experimental coronary thrombosis. In 46 open-chest dogs with a critical coronary stenosis produced by plicating the coronary artery wall with a suture, blood flow showed cyclical reductions followed by an abrupt return to control levels. The flow reduction were previously shown to be caused by platelet aggregation. In the present study they were unaffected by heparin (1,000 U . kg-1 . h-1) at the start of the experiment but consistently abolished by aspirin (30 mg . kg-1) at the end of the protocol, further supporting platelet aggregation as the primary mechanism. After 1 h of observation, dogs were assigned to one of the following groups: control (no intervention, n = 9), phentolamine (a nonselective alpha-blocker) "low dose" (0.07 mg . kg-1 bolus followed by 0.1 mg . kg-1 . min-1, n = 4), phentolamine "high-dose" (3 mg . kg-1 bolus followed by 0.07 mg . kg-1 . min-1, n = 6), prazosin (an alpha 1-blocker, 2 mg . kg-1, n = 8), yohimbine (an alpha 2-blocker, 3 mg . kg-1, n = 11) or prazosin + yohimbine (same doses, n = 8). In controls, cyclical reductions in flow continued unchanged for another hour. Phentolamine effected a partial dose-related inhibition of flow reductions; however, prazosin and yohimbine, given separately or in combination, failed to produce any significant effect despite an alpha-blocking action equivalent to or greater than that of phentolamine (alpha-agonist dose-response studies).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of the stable prostacyclin analogue ZK 36374 on experimental coronary thrombosis in the pig

The hemodynamic and antithrombotic action of ZK 36374,a stable carbacyclin derivative of prostacyclin, was studied during electrically-induced coronary artery thrombosis in the open chest anesthetized pig. Infusion of ZK 36374 (100 ng/kg/min, n=6) had no effect on heart rate and cardiac output, but caused a 20% reduction in mean arterial blood pressure by peripheral vasodilation. In animals receiving solvent or no drug prior to thrombosis induction, the time to occlusive coronary artery thrombosis (TOT) was 30 ± 2 minutes (mean ± SEM, n=17). Pretreatment with an i.v. infusion of ZK 36374 (100 ng/kg/min) prolonged TOT by 50% to 47 ± 7 minutes (p< 0.005, n=6). This prolongation of TOT was not due to the lower blood pressure in the ZK 36374 group, as dihydralazine in a dose that lowered arterial blood pressure to the same extent had no effect on TOT (32 ± 4 minutes, n=4). The results indicate that ZK 36374 may be useful in delaying (or preventing) occlusive coronary artery thrombi.

The beneficial effects of nafazatrom (BAYg6575) on experimental coronary thrombosis

An in vivo model of coronary artery thrombosis in the conscious dog was used to evaluate the potential antithrombotic effect of nafazatrom (BAYg6575). A silver wire electrode was implanted in the left circumflex coronary artery (LCX) and was used at a later time to deliver a 50 uA anodal current for 24 hours to the intimal surface of the vessel. The resulting injury to the endothelium was accompanied by the adhesion, aggregation, and subsequent formation of an occlusive thrombus in the LCX of vehicle-treated dogs. Nafazatrom was given as an intravenous dose of 1 mg/kg for 48 hours, before anodal stimulation of the coronary artery was initiated, and was repeated every 6 hours during anodal stimulation for a total treatment period of 72 hours. As compared to vehicle-treated control dogs, the dogs treated with nafazatrom had smaller thrombi, preservation of coronary blood flow, a lesser degree of ischemic injury in the myocardial region subserved by the LCX, and less frequent premature ventricular complexes during the final 12 hours of the study period. Concomitant ex vivo platelet aggregation studies revealed significant inhibition of platelet aggregation in response to collagen and adenosine diphosphate in drug-treated dogs. The results of these investigations provide evidence that nafazatrom prevents in vivo development of occlusive coronary artery thrombi in response to disruption of the endothelial surface of the vessel.

A New Method for Experimental Coronary Thrombosis in the PIG

A New Method for Experimental Coronary Thrombosis in the PIG

Serotonin blockade during experimental coronary thrombosis

The protective effect of methysergide on accumulating serotonin within the myocardium, during acute and chronic coronary thrombosis was evaluated in two groups of dogs. The first group of 15 dogs was pretreated with methysergide (100 μg/Kg. B.W., intravenously) and an equal number of dogs in the second group served as the control. An occluding intracoronary thrombus was produced in each dog by the closed chest placement of a thrombogenic wire into the left anterior descending (LAD) coronary artery, via catheter technique, under x-ray visualization. Blood pressure (BP), heart rate (HR), cardiac output (CO), stroke volume (SV), total peripheral resistance (TPR), and contractile force ( dP dt ) were determined before and at 1, 3, and 5 hours (acute phase) after the onset of thrombosis. These variables were measured again at 1 and 8 days (chronic phase) after verified occlusion. The sums of the mean Q wave (ΣQ) and S-T segment (ΣS-T) amplitudes from 14 ECG precordial mapping sites were also calculated in six dogs of each group at these chronic time periods. Several biochemical variables were measured in the active phase from coronary venous blood specimens collected through the fifth hour. Histological examinations were also performed in the acute and chronic phases on control and pretreated hearts. During the aforementioned sampling times, certain hemodynamic variables decreased significantly (p < 0.05) in the control dogs, but less significant changes were found in the methysergide pretreated animals. There were similar differences in the mean concentration of certain biochemical variables between the two groups, in the acute stages of thrombosis, with less significant changes in the methysergide pretreated dogs. Generally, there were less necrotic changes in the methysergide hearts at the eighth day but histological differences between the two groups were inconclusive in the acute phase. It appears from this study that the cardiodynamic and biochemical integrity was sustained by blocking the action of serotonin within the affected myocardium during myocardial infarction due to thrombotic occlusion of the LAD coronary artery.

Effects of Experimental Coronary Thrombosis upon Regional and Systemic Plasma Chromatographic Patterns

An evaluation of changes in the plasma chromatographic pattern was carried out in dogs with experimental coronary thrombosis. Sequential samples were taken simultaneously from the aorta and coronary sinus over a two, four and twenty-four hour period. In addition to gel-chromatography, immunodiffusion and electrophoresis were also employed to identify the protein components of the elution fractions. The results showed that there was a shift of the normal chromatographic pattern to the left from the control within two hours following thrombotic occlusion of the coronary artery and it was maintained over a twenty-four hour period. The shift to the left was presumably due to the earlier elution of the heavy molecular weight components forming as a result of the thrombotic process. The early appearance of the altered chromatographic pattern constitutes an important advantage worthy of further exploration for possible diagnostic application in the human subject.

Effect of Experimental Coronary Thrombosis upon Platelet Kinetics

SummaryA study was designed to determine the effect of experimental coronary thrombosis upon quantitative changes of platelets in the coronary sinus blood and in the systemic circulation. In addition, using 51Cr-labelled platelets, their distribution in the organ primarily affected by the presence of thrombus, namely the heart, and organs known to be involved in platelet kinetics such as liver, spleen and lungs, was also examined. Following coronary occlusion, a consistent pattern of progressive decrease in platelet counts in the effluent of the infarcted area (coronary sinus) as well as in the systemic blood, maintained for at least 18-20 hours following the thrombotic event, was observed. There was a significant increase in platelet sequestration by spleen, liver and lung and presence of platelet thrombi in the microcirculation of the coronary arterial system. The results suggest that a thrombotic process in a medium size artery induces a more generalized involvement of the platelet population through mechanisms which are not clear at this time. The changes in platelet counts, following coronary thrombosis, obtained as described in this study offer diagnostic possibilities in cases where an active thrombotic process is suspected. However, further studies are necessary before the value of this diagnostic approach is established.

Effect of aspirin upon experimental coronary and non-coronary thrombosis and arrhythmia

The effect of aspirin upon platelet function led to speculation on the potential effects of salicylates upon arterial thrombogenesis, in which platelets play a primary role. Aspirin was given by mouth or intravenously before attempting induction of coronary or femoral artery thrombosis in dogs by means of a catheter electrode. The incidence of thrombus formation in all animals receiving aspirin was comparable to that of the control groups. Although in several animals of coronary thrombus group receiving aspirin, the thrombus was smaller than in the controls, this was not statistically significant. An unexpected finding was the distinct decrease in incidence of arrhythmias and ventricular fibrillation in the coronary thrombus group treated with aspirin. The reason for the differences is not clear at this time.

A new catheter technique for producing experimental coronary thrombosis and selective coronary visualization

A new catheter technique for producing experimental coronary thrombosis and selective coronary visualization

Streptokinase in myocardial infarction: A co-operative controlled australian trial

Experimental coronary thrombosis in dogs has been treated with thrombolytic therapy with considerable reduction in the extent of myocardial necrosis compared to that in control animals. Such a favourable result has not been demonstrated in human myocardial infarction although there have been many trials of thrombolytic agents in this condition. Most of these trials suffer from defects in methodology. A multicentre trial of Streptokinase in acute myocardial infarction was being conducted in four university teaching hospitals. Patients aged less than 65 yr. and with a diagnosis of myocardial infarction of less than 24 hr. duration were admitted to the trial providing there were no contra-indications to the use of Streptokinase. After admission to the trial they were randomly allocated to the treatment group (Streptokinase) or the control group (Heparin). Both agents were given in standard dosage. Evidence of adequate fibrinolysis in the Streptokinase group was based on thrombin clotting times and fibrin plate assays during the infusion. All patients were treated in coronary care units with continuous monitoring equipment, and following the initial infusion, anticoagulation was continued with Warfarin during hospitalization. Patients were assessed 3 mth. after their admission. The hospital mortality was 11 out of 125 (8.8%) in the Streptokinase and 14 out of 120 (11.7%) in the control group. At 3 mth. the overall mortality was 13 out of 99 (13.1 %) in the Streptokinase group and 19 out of 94 (20.2%) in the control group. These differences were not statistically significant. One hundred and twenty-six electrocardiograms of patients with proven infarction were analysed at 3 mth. Of 61 in the Streptokinase group, 14 had returned to normal, while 6 of 65 in the Heparin had returned to normal. This difference was significant. Although the reduction in mortality in the Streptokinase-treated group was not statistically significant at the time of the report, the results suggested an extension of the trial to be worthwhile.

Use of Trypsin in the Treatment of Experimental Coronary Thrombosis

A method for the production of experimental coronary thrombosis in dogs by the injection of thrombin into the anterior descending branch of the left coronary artery is presented. The clot-dissolving properties of trypsin in the form of Tryptar and Enzar were evaluated. The effect of trypsin was also studied in relation to changes in the clotting mechanism of the blood for the purpose of determining tolerated doses. Regardless of amounts of enzyme or time of administration, there was no evidence to indicate prevention of myocardial infarction.

Experimental coronary thrombosis in the dog; description of a method.

Gage, Andrew A. M.D.; Olson, Kenneth C. M.D.; Chardack, William M. M.D. Author Information

Intravenous trypsin in experimental myocardial infarction.

The possibility of using intravenous proteolytic agents in the treatment of acute myocardial infarction has been studied. The coronary arteries of closed-chest dogs were embolized with small repetitive doses of fibrin clots until definite electrocardiographic evidence of myocardial injury which persisted for at least two hours was observed. The treated animals were given up to six intravenous infusions of 250,000 Armour units of trypsin in 250 ml. saline over a period of eight days, and the survivors were sacrificed on the ninth day. The control animals received no trypsin. These studies showed that trypsin caused dissolution of the host thrombus which formed around the fibrin clots, without damage to the infarcted tissue; that the coronary vessels were recanalized; that the extent of infarction was decreased; and that the electrocardiographic changes were improved and the mortality was reduced.