Platelet function studies in coronary artery disease. V. Evidence for enhanced platelet microthrombus formation activity in acute myocardial infarction

Cerebral amyloid angiopathy-related cardiac injury: Focus on cardiac cell death

Cerebral amyloid angiopathy (CAA) is a kind of disease in which amyloid β (Aβ) and other amyloid protein deposits in the cerebral cortex and the small blood vessels of the brain, causing cerebrovascular and brain parenchymal damage. CAA patients are often accompanied by cardiac injury, involving Aβ, tau and transthyroxine amyloid (ATTR). Aβ is the main injury factor of CAA, which can accelerate the formation of coronary artery atherosclerosis, aortic valve osteogenesis calcification and cardiomyocytes basophilic degeneration. In the early stage of CAA (pre-stroke), the accompanying locus coeruleus (LC) amyloidosis, vasculitis and circulating Aβ will induce first hit to the heart. When the CAA progresses to an advanced stage and causes a cerebral hemorrhage, the hemorrhage leads to autonomic nervous function disturbance, catecholamine surges, and systemic inflammation reaction, which can deal the second hit to the heart. Based on the brain-heart axis, CAA and its associated cardiac injury can create a vicious cycle that accelerates the progression of each other.

Uridine Triphosphate Thio Analogues Inhibit Platelet P2Y12 Receptor and Aggregation

Platelet P2Y₁₂ is an important adenosine diphosphate (ADP) receptor that is involved in agonist-induced platelet aggregation and is a valuable target for the development of anti-platelet drugs. Here we characterise the effects of thio analogues of uridine triphosphate (UTP) on ADP-induced platelet aggregation. Using human platelet-rich plasma, we demonstrate that UTP inhibits P2Y₁₂ but not P2Y₁ receptors and antagonises 10 µM ADP-induced platelet aggregation in a concentration-dependent manner with an IC₅₀ value of ~250 µM. An eight-fold higher platelet inhibitory activity was observed with a 2-thio analogue of UTP (2S-UTP), with an IC₅₀ of 30 µM. The 4-thio analogue (4S-UTP) with an IC₅₀ of 7.5 µM was 33-fold more effective. A three-fold decrease in inhibitory activity, however, was observed by introducing an isobutyl group at the 4S- position. A complete loss of inhibition was observed with thio-modification of the γ phosphate of the sugar moiety, which yields an enzymatically stable analogue. The interaction of UTP analogues with P2Y₁₂ receptor was verified by P2Y₁₂ receptor binding and cyclic AMP (cAMP) assays. These novel data demonstrate for the first time that 2- and 4-thio analogues of UTP are potent P2Y₁₂ receptor antagonists that may be useful for therapeutic intervention.

Sticky platelet syndrome: an important cause of life-threatening thrombotic complications

Sticky platelet syndrome (SPS) is a prothrombotic thrombocytopathy with familial occurrence, characterized by hyperaggregability of platelets in response to adenosine diphosphate (ADP), epinephrine (EPI) or both. The syndrome has been identified in approximately 21% of unexplained arterial thrombotic episodes, regarded to be the most common thrombophilia in arterial thrombosis and 13.2% of unexplained venous thromboembolism (VTE). The relatively young age at the first manifestation, relation to fertility and pregnancy, seriousness of the symptoms, easy and effective management of the disorder indicate to the necessity to take it into account in the differential diagnosis of the underlying cause of the thrombotic event. As the various localizations of the thrombosis in SPS have been reported, its management often requires a multidisciplinary approach. This review deals with the clinical aspects of thrombophilia, its etiopathogenesis, diagnosis as well as novel advances in the treatment and outlines the challenges for the further research.

Platelet counts in myocardial infarction, angina pectoris and peripheral artery disease

Serial determinations of peripheral venous platelet counts were performed in 43 consecutive patients with acute chest pain. On admission, patients with acute myocardial infarction (AMI) had a significantly lower mean platelet count (p less than 0.05). Thereafter a further reduction was seen with steadily reduced platelet counts by about 20%, both in comparison with healthy controls (p less than 0.001) (n = 113) and patients with peripheral artery disease (PAD) without heart symptoms (p less than 0.005) (n = 54). The platelet number increased one week after admission and even thrombocytosis was observed. The changes in platelet number during AMI seem to parallel the changes in platelet function. Patients with PAD had normal mean platelet counts. Female patients as well as healthy subjects had significantly higher values than men (p less than 0.01).

Isosorbide dinitrate inhibits platelet adhesion and aggregation in nonthrombolyzed patients with acute myocardial infarction

BACKGROUND

Apart from their vasodilatatory properties, nitrates have been shown to inhibit platelet aggregation. The effects of nitrates on platelet adhesion have not been studied. Nonselected patients with acute myocardial infarction (AMI) have been suggested to gain no benefit from administration of nitrates. However, the importance of nitrates may be greater in a subgroup of nonthrombolyzed patients with AMI.

HYPOTHESIS

Isosorbide dinitrate (ISDN) decreases platelet adhesion and aggregation in nonthrombolyzed patients with AMI.

METHODS

Consecutive 48 men with AMI, not eligible for thrombolytic therapy because of late presentation (> 12 h), were prospectively randomized 2:1 to double-blind ISDN (mean dose 2.4 +/- 0.9 mg/h) (n = 33) or placebo (0.9% sodium chloride) (n = 15) infusion. All patients received aspirin. Blood samples were taken at baseline (no study medication) and 3 h into ISDN or placebo infusion. Platelet adhesion to collagen was measured in the ethylene diamine tetraacetic acid (EDTA)-platelet rich plasma by recording changes in light transmission with an optical aggregometer. Platelet aggregation was measured using the Born's method.

RESULTS

Isosorbide dinitrate significantly decreased both platelet adhesion and aggregation. No effect was seen in the placebo group.

CONCLUSIONS

In patients with AMI who do not receive thrombolytic therapy, ISDN effectively inhibits platelet adhesion and aggregation. These effects of nitrates may be of therapeutic and prognostic significance in this group of patients.

Changes in platelet ATP secretion and aggregation during pregnancy and in preeclampsia

BACKGROUND

Platelet secretion plays an important role in the aggregation of platelets. However, the quantitative relationship between platelet aggregation and secretion of ATP during pregnancy and in pre-eclampsia has yet to be clarified. This study is designed to determine whether platelet count, volume, aggregation, and the amount of secreted ATP change in healthy, nonpregnant women, nonpreeclamptic pregnant women, and preeclamptic pregnant women and whether beta-thromboglobulin (BTG) and platelet factor 4 (PF-4) concentrations alter in nonpreeclamptic and pre-eclamptic women.

METHODS

Peripheral blood was collected from 114 women. Nonpreeclamptic pregnant women were divided into four groups (gestational weeks 10, 20, 30, and 35). Platelet aggregation and ATP secretion were investigated with the use of a lumi-aggregometer. BTG and PF-4 concentrations in peripheral blood were determined in 12 pregnant and 11 preeclamptic women.

RESULTS

The amount of secreted ATP upon induction by 5 microM ADP increased significantly (P < 0.05-0.01) with gestational age. On the other hand, the amount of secreted ATP induced by 5 microg/mL collagen reached the maximal value from gestational weeks 20 to 35 in nonpreeclamptic women. Significantly more platelet aggregation was induced by the ADP and collagen in nonpreeclamptic women in gestational weeks 20 and 30 than in the gestational weeks 10 or 35 (P < 0.05-0.005). The amount of secreted ATP and platelet count were significantly lower (P < 0.05) in preeclampsia than in normal pregnancy. The BTG and PF-4 concentrations were significantly higher (P < 0.05) in preeclampsia than in normal pregnancy.

CONCLUSIONS

The sensitivity of platelets for ATP secretion may intensify with progression of pregnancy. In normal pregnancy, around gestational week 35, the platelets may exhibit weaker ability to aggregate but maintain the capacity to secrete ATP. In preeclampsia, secreted ATP decreased because platelets may be stimulated to undergo a partial secretion.

Comparative study of toborinone (OPC-18790) and milrinone on energy metabolism in microembolized guinea pig hearts

The effects of toborinone (OPC-18790) and milrinone on cardiac function and energetics were compared in microembolized guinea pig hearts. Male guinea pig hearts were perfused according to the Langendorff method and microembolization was induced by injecting microspheres. The hearts were then treated with toborinone (10 microM), milrinone (4 microM), and vehicle. Energy metabolism in hearts was assessed by 31-phosphorus magnetic resonance spectroscopy (31P-MRS). Microembolization produced a decrease in coronary perfusion flow (CPF), left ventricular developed pressure (LVP), and peak LVdP/dt by about 50% concomitantly with a decrease in creatine phosphate (PCr) and ATP and an increase in inorganic phosphate (Pi) and Pi/PCr ratio. Toborinone and milrinone increased peak LVdP/dt, an index of contractility, by 15 +/- 2% and 18 +/- 3%, respectively. Milrinone increased heart rate (HR) by 22 +/- 4% but toborinone did not change HR. Toborinone did not change PCr, ATP, Pi, Pi/PCr, and intracellular pH (pHi) compared with the vehicle. On the other hand, milrinone decreased PCr and increased Pi and Pi/PCr compared with toborinone or vehicle. These results suggest that the different effects between toborinone and milrinone on energy metabolism in microembolized hearts may be due to the difference of chronotropic action between these drugs. Thus toborinone, a positive inotropic agent without chronotropic action, may be effective in acute treatment of ischemic heart failure.

Effects of atrioventricular asynchrony on platelet activation: implication of thromboembolism in paced patients

OBJECTIVE

To investigate the platelet activation in different modes of pacing in patients implanted with dual chamber rate adaptive pacemaker (DDDR) for bradyarrhythmias, and to explore the possible underlying mechanism of the higher thromboembolic incidence in single chamber ventricular rate adaptive (VVIR) pacing.

DESIGN

Platelet activation was determined in chronically paced patients during three different pacing modes (VVIR, DDD, and DDDR) in a randomised crossover fashion.

SETTING

Pacemaker clinic at a university teaching hospital.

PATIENTS

15 patients with complete heart block, mean (SD) age 63 (10) years, and 12 patients with sick sinus syndrome, mean age 68 (9) years, implanted with DDDR pacemakers.

MAIN OUTCOME MEASURES

Platelet activation was assessed by measuring the plasma concentrations of platelet factor 4 (PF4) and beta thromboglobulin using an enzyme linked immunosorbent assay (ELISA). Mean log plasma PF4 and beta thromboglobulin values were compared in paced patients during different pacing modes and with controls.

RESULTS

Compared with controls, patients paced in DDDR, DDD, and VVIR modes had higher mean log plasma concentrations of PF4 (0.90 (0.32), 0.92 (0.29), and 1.12 (0.33) v 0.61 (0.29) log IU/ml, all p < 0.05, respectively) and beta thromboglobulin (1.55 (0.20), 1.59 (0.16), and 1.71 (0.18) v 1.40 (0.12) log IU/ml, all p < 0.05, respectively). In paced patients, VVIR pacing was associated with higher plasma concentrations of PF4 and beta thromboglobulin than either DDDR or DDD pacing (all p < 0.05). There was no significant difference in plasma PF4 and beta thromboglobulin between patients with complete heart block and sick sinus syndrome in the corresponding pacing mode. Holter monitoring showed no difference in mean pacing rate and occurrence of cardiac arrhythmias to account for the increased platelet activation during VVIR pacing. There was no relation between the percentage of ventricular pacing on Holter during DDDR, DDD, and VVIR modes and the log mean plasma concentrations of PF4 (r = 0.002, 0.001, and 0.001, respectively, all p > 0.05) and beta thromboglobulin (r = 0.007, 0.01, and 0.001, respectively, all p > 0.05).

CONCLUSIONS

Single chamber ventricular pacing was associated with enhanced spontaneous systemic platelet activation compared with physiological dual chamber pacing. This was related to the loss of atrioventricular synchrony rather than to the underlying cause of bradycardia, lack of rate response, or coexisting arrhythmia. This abnormality may be associated with increased thromboembolism and was correctible by an appropriate pacing mode prescription and possibly antiplatelet treatment.

Platelet function in acute myocardial infarction treated with direct angioplasty

BACKGROUND

In acute myocardial infarction (AMI), platelets play a key role in thrombotic processes that limit the patency of the recanalized, infarct-related coronary artery and contribute to reperfusion injury. Platelet function in the course of AMI treated by direct percutaneous transluminal coronary angioplasty (PTCA) has not been evaluated.

METHODS AND RESULTS

In 15 patients with anterior AMI, peripheral venous blood samples were obtained before and 4, 8, 24, and 48 hours after recanalization of the occluded artery by PTCA. Fifteen patients who had stable coronary heart disease and were undergoing elective balloon angioplasty served as control subjects. Fibrinogen receptor function and surface expression of P-selectin on platelets were determined by flow cytometry. In addition, we evaluated generation of platelet-derived microparticles and the effect of systemic plasma from patients with AMI on normal platelet function and on platelet adhesion to human endothelial cells in culture. We found fibrinogen receptor activity and P-selectin expression on circulating platelets 8 hours after direct PTCA are decreased (P < .01). This coincided with a decrease in peripheral platelet count (P < .05) and an increase in generation of microparticles (P < .002). Twenty-four to 48 hours after PTCA, fibrinogen receptor activity and P-selectin expression increased again. Systemic plasma obtained before and after direct PTCA sensitized normal platelets to hyperaggregate in vitro (P < .001) and stimulated platelet adhesion to endothelial cells in culture (P < .01). None of the changes found in AMI were detectable in the control group.

CONCLUSIONS

After transient apparent deactivation of circulating platelet, probably caused by sequestration of hyperactive platelets, the level of platelet activation increases in patients with AMI treated by direct PTCA. These findings underscore the need for novel antiplatelet strategies in AMI.

Platelet activation during myocardial ischaemia: a contributory arrhythmogenic mechanism

Experimental and clinical observations of the involvement of platelets in the pathophysiology of myocardial ischaemia indicate the importance of interactions between these formed elements and the heart. The aim of this review is to outline evidence linking platelet activation, myocardial ischaemia and infarction, and to present evidence for a link between platelet activation, arrhythmogenesis and sudden death. A brief review of platelet physiology and pharmacology is provided, with a review of the cardiac electrophysiological effects of ischaemia and the electrophysiological effects of platelet-derived substances. The concept that platelet activation during myocardial ischaemia is a contributory arrhythmogenic mechanism is discussed.

Calcium supplementation attenuates an enhanced platelet function in salt-loaded mildly hypertensive patients

We designed this study to evaluate the effect of low versus high calcium intake on platelet function in salt-loaded patients with mild hypertension. After a 7-day period of dietary salt restriction, 19 patients were placed on a high salt (300 mmol/d), low calcium (6.25 mmol/d) diet for 7 days; 10 of these patients were given 54 mmol/d of supplementary calcium, and 9 patients were given placebo. At the end of the low and high salt regimens, we evaluated changes in blood pressure, platelet aggregation, and the platelet release reaction measured as plasma beta-thromboglobulin and platelet factor 4 levels. With high salt intake, significant increases in mean blood pressure (P < .02), red blood cell sodium (P < .01), and platelet aggregation induced by 3 mumol/L ADP (P < .01) and by 3.0 mg/L epinephrine (P < .05) were observed in the placebo-treated patients but not in the calcium-supplemented ones. Compared with the placebo-treated patients, calcium-supplemented patients had a smaller weight gain (P < .05) but excreted more sodium and calcium (P < .01) at the end of the high salt regimen. Calcium supplementation resulted in decreases in beta-thromboglobulin (P < .05), platelet factor 4 (P < .01), and plasma and urinary excretions of norepinephrine (P < .02) during the high salt, low calcium regimen. The decrease in plasma norepinephrine correlated positively with the decreases in beta-thromboglobulin (r = .72, P < .02) and platelet factor 4 (r = .85, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet glycoprotein IIb-IIIa and size are increased in acute myocardial infarction

Platelet aggregation, which plays an important role in acute myocardial infarction (AMI), is mediated by fibrinogen binding to the platelet membrane glycoprotein (GP)IIb-IIIa (CD41). This study measured the relative number of GPIIb-IIIa complexes on platelets from patients immediately following AMI (n = 14) compared with those from controls (n = 14). Flow cytometry was used to demonstrate that there were, on average, 20% more GPIIb-IIIa complexes on platelets after AMI compared with controls. Platelet size was also 7% greater in AMI and it is known that larger platelets are more reactive. Since platelet size and protein content are determined at thrombopoiesis the majority of these platelets must have been circulating prior to AMI. Larger platelets, with more GPIIb-IIIa may, therefore, be causally related to AMI.

Effects of the PAF antagonists BN50726 and BN50739 on arrhythmogenesis and extent of necrosis during myocardial ischaemia/reperfusion in rabbits

1. The effects of two novel platelet activating factor (PAF) antagonists BN50726 and BN50739 on arrhythmias, haemodynamics and extent of necrosis during myocardial ischaemia and reperfusion were investigated in anaesthetized rabbits subjected to coronary artery ligation. 2. BN50739 reduced heart rate prior to coronary artery occlusion (P < 0.005) but had no other significant haemodynamic effects at this time. BN50739 and BN50726 did not significantly alter heart rate or blood pressure during 30 min of ischaemia or 30 min of reperfusion, compared to control hearts. 3. BN50739 and BN50726 had no effect on the incidence of arrhythmias during ischaemia. BN50726 significantly reduced the incidence of reperfusion ventricular fibrillation compared to controls (0% v 40%, P < 0.05), and improved survival (80% v 39%, P < 0.05). Similar trends were observed with BN50739. 4. BN50726 reduced the extent of necrosis compared to control hearts (18 +/- 2% v 30 +/- 3%, P < 0.01). A similar trend was observed with BN50739. 5. These results demonstrate that PAF antagonism with BN50726 attenuates reperfusion-induced arrhythmias and preserves myocardium in the early phase of ischaemia, independently of haemodynamic effects.

Circulating aggregated platelets, number of platelets per aggregate, and platelet size during acute myocardial infarction

Circulating aggregated platelets (total, reversibly and irreversibly aggregated), the number of platelets per aggregate and "big" platelets were measured by a modification of the Wu and Hoak method in 42 patients on the first, second and fifth day of acute myocardial infarction (AMI). Among them, 30 had an uncomplicated course and 12 patients had complications that occurred between the 5th and 10th day of hospitalization (7 patients had reinfarction and 5 died). In all patients the measured parameters were elevated compared with those of control subjects. There was a significant increase, especially after the first observation day, in the values of total aggregated platelets (37 +/- 11% vs 26 +/- 12%, p < 0.001), reversibly aggregated platelets (27 +/- 9% vs 17 +/- 8%, p < 0.001) and the average platelets per aggregate (8.6 +/- 0.3 vs. 2.3 +/- 0.4) in patients with versus without complications. In considering the role of platelets in the development of AMI, these findings may add information to the role of platelets in determining the course of AMI.

Metoprolol does not reduce platelet aggregability during sympatho-adrenal stimulation

The possibility that beta-adrenoceptor blockers, especially beta 1-selective agents might inhibit platelet function is of considerable interest, as this might be of pathophysiological importance in cardiovascular diseases. Platelet function, however, is difficult to assess and in vivo related data are scarce. The effect of one week of treatment with metoprolol 200 mg/day on platelet aggregability during mental stress (colour word conflict test; CWT) and low and high dose adrenaline infusions has been evaluated in a double-blind, placebo-controlled, cross-over study in 10 healthy male volunteers. Platelet function in vivo was assessed using ex vivo filtragometry, and the urinary excretions of beta-thromboglobulin (HMW beta-TG) and 11-dehydro-TxB2 (a thromboxane metabolite). Conventional in vitro aggregometry and the urinary levels of 2,3-dinor-6-keto-PGF1 alpha (a prostacyclin metabolite) were also studied. During the interventions there was increased platelet aggregability in vivo, as filtragometry readings were shortened by 41 +/- 11% during high dose adrenaline infusion, urinary HMW beta-TG levels increased and urinary 11-dehydro-TxB2 tended to increase. In contrast, platelet sensitivity to ADP in vitro was reduced. The urinary 2,3-dinor-6-keto-PGF1 alpha levels were increased during the interventions. Despite the cardiovascular and biochemical signs of beta-adrenoceptor blockade at rest and during the interventions, metoprolol failed to influence platelet function in vivo, as measured by ex vivo filtragometry, or urinary HMW beta-TG or 11-dehydro-TxB2 levels. It tended rather to enhance the stress response measured by ex vivo filtragometry. Platelet aggregability in vitro and urinary 2,3-dinor-6-keto-PGF1 alpha levels were not altered by metoprolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet-leukocyte-endothelial interactions in coronary artery disease

It is generally recognized that formation of a platelet-fibrin-rich thrombus in an atherosclerotic coronary artery is the basis of unstable angina and acute myocardial infarction. Platelet hyperactivity has been identified in coronary risk factors such as hyperlipidemia and diabetes mellitus. Persistent activation of these cells results in release of growth factors that may contribute to the progression of atherosclerosis. Several recent studies show that endothelium, by generating or metabolizing a host of vasoactive substances, plays a critical role in the modulation of vascular tone. Important among these substances are prostacyclin (PGI2) and endothelium-derived relaxing factor (EDRF). The endothelium-dependent modulation of coronary artery tone correlates with the severity of atherosclerosis and the number of coronary risk factors. Procedures such as angioplasty and coronary bypass surgery injure the endothelium. The loss of endothelial smooth muscle relaxant function may contribute to the vasoconstriction and thrombosis often observed soon after these procedures. Thrombolysis (and subsequent reperfusion of the coronary artery) is also associated with severe endothelial dysfunction, with a resulting vasoconstrictor influence on the coronary vascular bed. Activation of leukocytes and their presence in the reperfused myocardium contribute to progression of myocardial injury by release of oxygen free radicals and proteolytic enzymes. Thus, it seems that a perturbation in this delicate equilibrium in cellular interactions relates to genesis and progression of myocardial ischemia.

Electrophysiological and arrhythmogenic effects of platelet activating factor during normal perfusion, myocardial ischaemia and reperfusion in the guinea-pig

1. Platelet activating factor (PAF) is often used to study the effects of platelet activation. While direct myocardial electrophysiological effects of PAF have been described in superfused myocardial tissue, little is known about its actions on the whole heart. 2. The cellular electrophysiological and arrhythmogenic effects of PAF (10(-11)M, 10(-10)M and 10(-9)M) were studied during normal perfusion, global myocardial ischaemia and reperfusion in Langendorff-perfused guinea-pig hearts at 32 degrees C. 3. PAF (10(-9)M) increased the incidence of ventricular fibrillation during ischaemia and reduced action potential duration (APD) during normal perfusion and early myocardial ischaemia (10(-9)M and 10(-10)M). PAF also reduced refractory period (RP) during normal perfusion (10(-9)M) and early ischaemia (10(-9)M and 10(-10)M). PAF prevented recovery of APD (10(-9)M) and RP (10(-9)M and 10(-10)M) during reperfusion. PAF at a concentration of 10(-11)M had no electrophysiological effects. 4. PAF (10(-9)M) increased the QRS width of the electrocardiogram during late ischaemia while 10(-10)M PAF raised pacing threshold during late ischaemia. 5. Perfusion pressure was increased, and developed tension decreased by 10(-9)M PAF. 6. These results demonstrate that PAF has direct myocardial electrophysiological effects in the whole heart which occur during normal perfusion and are capable of augmenting the effects of myocardial ischaemia, but are independent of the presence of platelets.

Platelet calcium and quenched-flow aggregation kinetics in essential hypertension

Abnormal platelet function may contribute to the complications of essential hypertension. We have studied the kinetics of platelet aggregation induced by adenosine diphosphate (ADP) or epinephrine, plasma beta-thromboglobulin, and basal, cytosolic, and free calcium, as correlates of platelet function. Fifteen untreated patients with essential hypertension and without detectable atherosclerosis, 18-40 years old, were compared with 30 matched normotensive control subjects. Maximal rates of platelet aggregation (Vmax) with ADP and epinephrine were significantly higher in patients than in control subjects (p less than 0.03), as assessed by quenched-flow aggregometry. However, significance was lost when Vmax was corrected for the platelet count. Paradoxically, the activation constants (Ka) for ADP were higher in patients than in control subjects (p less than 0.03). With ADP as the inducing agent, onset time (t) or lag period before aggregation begins was longer in patients than in control subjects (p less than 0.02). beta-thromboglobulin levels, an index of in vivo platelet activation, were not significantly different between the two groups (p = 0.13). The mean platelet cytosolic free calcium concentration was higher in patients (213 +/- 19 nM) than in control subjects (172 +/- 14 nM), but this difference was not statistically significant (p = 0.07). However, there was a close correlation between the free calcium level and systolic, diastolic, and mean blood pressure (p less than 0.003, p less than 0.04, p less than 0.004, respectively). No difference in platelet volume between the two groups was found. Our data suggest that platelets in the early stages of essential hypertension display an overall increased aggregation potential but a diminished sensitivity to ADP.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary thrombosis and platelet/fibrin microemboli in death associated with acute myocardial infarction

The frequency and clinical significance of platelet/fibrin microemboli in the microcirculation were investigated in 24 patients whose deaths (before and during hospital admission) were associated with acute myocardial infarction. An acute coronary thrombus was present in all the hearts. In nine hearts an acute thrombus was found in more than one major epicardial coronary artery. A total of 35 acute thrombi were found in the 24 hearts. Platelet/fibrin microemboli were found in 19 (79%) hearts. Eighteen patients died in hospital. The hearts of 16 of these cases showed microemboli; 16 had important arrhythmias or various forms of heart block; 13 showed acute pathological changes in the conduction system. Fourteen of the deaths in hospital were primarily the result of cardiogenic shock and four were primarily caused by arrhythmia. Six of the deaths that occurred before admission to hospital were regarded as being arrhythmic in origin. Three of these showed microemboli and the other three had acute pathological changes in the conduction system. Microemboli were found in two (24%) of 12 control hearts. Coronary thrombosis was found in most deaths caused by acute myocardial infarction and platelet/fibrin microemboli were present in the majority of such hearts. These may arise from the coronary thrombus in the larger upstream vessel supplying the microcirculation.

Response of some haemocoagulatory and haemorheological variables to maximal exercise in sedentary and active subjects

The purpose of this study was to evaluate how physical conditioning is associated with haemostatic and rheological responses to strenuous exercise. A total of 25 males, divided into two groups differing in exercise fitness (14 sedentary and 11 active), underwent exercise testing on a bicycle ergometer with an initial 25 W workload increasing by the same amount every 3 min. The following variables were evaluated before and after the test: platelet count and aggregability, plasma fibrinogen, fibrinolytic degradation products, viscometry and micro-haematocrit. Significant differences in baseline values between the two groups were found only for blood viscosity. Irrespective of the group, significantly increased values were demonstrated for all the variables, except platelet aggregability and fibrinogen levels, in response to strenuous exercise. It is concluded that the possible protective effect of exercise against cardiovascular disease does not seem to be related to changes in the haemorheological and haemostatic measures evaluated.

Circulating aggregated platelets in coronary artery disease

Circulating aggregated platelets were assessed in 30 patients with stable angina, 22 with unstable angina and 50 with acute myocardial infarction (AMI). Fifty healthy volunteers and 20 noncardiac patients served as controls. One milliliter of venous blood was separated into 2 solutions: 1 composed of ethylenediamine tetraacetic acid (EDTA) and formalin containing reversible and aggregates and 1 composed of EDTA alone containing irreversible aggregates only. By direct microscopic readings the percentage of platelets forming aggregates/1,000 counted platelets was determined in the 2 solutions. The number of reversibly aggregated platelets was estimated by subtracting the percentage of aggregated platelets in the second solution from that in the first solution. In patients with stable angina the percentage of aggregated platelets was higher than in control subjects (15 +/- 4% vs 7 +/- 2%, p less than 0.001). Most aggregated platelets (72% and 76%, respectively) were irreversibly aggregated. In the unstable angina group the percentage of aggregated platelets was similar to that of the AMI group (24 +/- 13% and 24 +/- 10%) and significantly higher than in the stable angina group. Only 11% and 17% of aggregated platelets in patients with stable angina and AMI were irreversibly aggregated and 89% and 83% of them were reversibly aggregated. Participation of platelets in the pathogenesis of unstable angina and AMI may be related to the early reversible phase of platelet activation.

Tissue plasminogen activator promotes platelet disaggregation in plasma

We studied the disaggregation of human platelets by tissue-type plasminogen activator (t-PA). When added to a suspension of human platelets induced to aggregate in plasma with adenosine 5'-diphosphate, t-PA promoted disaggregation of platelets over several minutes. Addition of fresh plasma or purified human fibrinogen to disaggregated platelets facilitated (reversible) aggregation and subsequent disaggregation. Aspirin treatment of platelets markedly potentiated the ability of t-PA to induce disaggregation. Disaggregation was inhibited by alpha-2-antiplasmin. Comparative analysis of the rate of proteolysis of platelet-bound fibrinogen with that of ambient plasma fibrinogen suggested that fibrinogenolysis of cohesive fibrinogen occurred more rapidly than fibrinogenolysis of ambient fibrinogen. These data demonstrate that t-PA facilitates platelet disaggregation in plasma through kinetically selective proteolysis of cohesive fibrinogen by plasmin, and suggest that thrombolytic mechanisms may serve both to remove platelets from platelet-fibrin thrombi and to disperse circulating platelet aggregates.

Formation of prostacyclin-sensitive platelet aggregates in human whole blood in vitro. Part II. The occurrence of the phenomenon in males suffering from acute myocardial infarction

The de-aggregatory effect of prostacyclin (PGI2) and the rate of spontaneous platelet aggregation (SPA) were studied in vitro in whole blood of 24 males with acute myocardial infarction (MI) and 18 males, patient controls (PC). The de-aggregatory effect of PGI2 and the rate of SPA (measured as a percentage of changes in free platelet number in whole blood) were higher (p less than 0.01) in MI than PC. The de-aggregatory effect of PGI2 in whole blood was higher (p less than 0.05) on the first day of MI than on day 14 following MI. The highest de-aggregatory effect of PGI2 was found in whole blood of patients with MI complicated by ventricular fibrillation. In neither of the groups did the de-aggregatory effect of PGI2 correlate with patients' age, haematocrit, erythrocyte and leucocyte counts, triglycerides, HDL, LDL or total cholesterol levels. In the MI group, de-aggregatory effect of PGI2 was correlated with free platelet concentration (r = -0.59, p less than 0.05), elevation of glutamic oxalacetic transaminase (r = 0.53, p less than 0.05) and creatinine phosphokinase (r = 0.69, p less than 0.001). The de-aggregatory effect of PGI2 in blood of patients with evolving MI did not differ from that in PC. It is concluded that the increased rate of SPA and formation of PGI2-sensitive platelet aggregates in vitro in whole blood of MI patients are secondary to myocardial necrosis.

Circulating platelet aggregate size in ischemic heart disease

Platelet aggregate size was measured in 178 patients with ischemic heart disease, among whom 56 had stable angina, 42 suffered from unstable angina, and 80 had had uncomplicated acute myocardial infarction. A group of 50 healthy volunteers and 20 hospitalized noncardiac patients served as controls. Venous blood (0.5 cc) was introduced into a solution containing 11.7 mM EDTA and 1.0 g formaldehyde. Platelet aggregate size was determined by microscopic reading as the number of platelets forming aggregates (per 1000 counted platelets) divided by the number of aggregates. Mean aggregate size was found not significantly different in both control groups, as well as in patients with stable angina and acute myocardial infarction (2.21 +/- 0.36 platelets, 2.20 +/- 0.58 platelets, 2.28 +/- 0.19 platelets, 2.76 +/- 1.07 platelets, respectively, p = NS). The highest value was found in the unstable angina group: 4.00 +/- 1.40 platelets (p less than 0.001 vs other studied groups). Platelet aggregate size was found not to be related to sex, age, medication, or coronary risk factors. Unstable angina may thus be a unique entity in ischemic heart disease concerning its platelet behavior, demonstrated in this study by the increased size of peripheral platelet aggregates, which may have pathogenetic, diagnostic, and eventual therapeutic implications.

Platelet hyperaggregability in patients with chest pain and angiographically normal coronary arteries

Forty-one patients with chest pain and angiographically normal coronary arteries were studied for platelet abnormalities. Patients with conditions known or suspected to be associated with chest pain or platelet dysfunction were excluded. After coronary angiography and 2-week withdrawal from all medications, platelet aggregometry was performed using peripheral venous plasma samples and 3 concentrations of adenosine diphosphate, 2.34, 1.17 and 0.58 microM, and epinephrine, 11, 1.1 and 0.55 microM, as stimuli. Platelet morphology in response to surface contact (adhesion) was evaluated by transmission electron microscopy to determine the percentage of platelets in the round/abortive (inactive), dendritic (intermediate) and spread (activated) forms. Plasma specimens obtained from healthy volunteers of similar age and sex were analyzed in parallel and served as control subjects. Compared with control subjects, patients had increased aggregation at all concentrations of both adenosine diphosphate and epinephrine (p less than 0.001). Patients also had fewer platelets in the dendritic form and more in the round/abortive and spread forms. Thus, patients with chest pain and normal coronary arteries have platelet hyperaggregability in vitro, although the clinical relevance of this finding is unclear.

Augmented thromboxane A2 generation and efficacy of its blockade in acute myocardial infarction

Serial changes in thromboxane B2, a stable catabolite of thromboxane A2, were measured by radioimmunoassay in peripheral plasma of 55 patients with acute myocardial infarction. Twenty two of 31 patients who were admitted within 6 hr after the onset of acute myocardial infarction, exhibited high thromboxane B2 levels (greater than 300 pg/ml plasma) during the first 24 hr, whereas thromboxane B2 levels of 9 patients never exceeded 300 pg/ml during that period. The former cases were associated with a higher frequency of transmural myocardial infarction, accompanying higher cumulative creatine kinase release (1173 +/- 134 mIU/ml, mean +/- SEM), as compared with the latter cases (393 +/- 104 mIU/ml, P less than 0.001). To evaluate the efficacy of selective thromboxane A2 blockade on diminution of propagating acute myocardial infarction, another group of patients (24 cases) showing transmural myocardial infarction were subjected to therapeutic examination employing OKY-1581, a potent thromboxane A2 synthetase inhibitor. Eleven randomly selected patients were treated with an infusion of OKY-1581 (initiated within 6 hr after onset, 2-3 micrograms/kg per min) for 48 hr, while 13 patient served as controls. The treated patients exhibited a precipitous decrease in thromboxane B2 levels, as compared with the controls, returning to the normal range within 12 hr. The creatine kinase release in the treated patients was markedly reduced (978 +/- 97 mIU/ml) as compared with that in the control patients (1295 +/- 95 mIU/ml, P less than 0.05). These results indicate that a marked increase in thromboxane B2 levels is seen during the early phase of transmural myocardial infarction, and that OKY-1581-induced reduction of thromboxane B2 levels is effective in diminishing creatine kinase release. We suggest that an excessive generation of thromboxane A2 is associated with the evolution of transmural myocardial infarction.

Failure of percutaneous transluminal coronary angioplasty to stimulate platelet and prostaglandin activity

Platelet function and prostaglandin activity were evaluated in nine patients with coronary artery disease undergoing percutaneous left anterior descending coronary artery angioplasty (PTCA) and compared to nine normal controls. Transcoronary measurements (arterial-coronary sinus) of platelet counts, mean platelet volume, platelet factor 4 (PF4), beta thromboglobulin, thromboxane (B2), and 6-keto-PGF 1 alpha were made. When compared to normal controls, the patients with coronary artery disease had higher circulating baseline levels of PF4 in the coronary sinus. There was no transcardiac production of any factor at baseline or immediately after infusion of nitroglycerin or performance of PTCA. These results suggest that PTCA does not grossly alter arachidonic acid metabolism or platelet activity.

Prostaglandin I2 (PG I2) fails to inhibit ADP induced platelet aggregation in vivo in rats

There is a simple method of inducing cardiopulmonary dysfunction in rats through platelet aggregation after rapid i.v. administration of ADP and thrombin. Infusion of 25 ng/min/kg PGI2 completely inhibited the decrease of both breathing and heart rate induced by 30 IU/kg thrombin. The same PGI2 infusion failed to influence the cardiopulmonary effects of the different ADP doses (between 75 and 0.1 mg/kg). Some possible reasons for the differential effectiveness of PGI2 are discussed on the basis of the modes of action of ADP, thrombin, and PGI2. The results stress the necessity of testing antiaggregatory substances in in vivo models.

Coagulant activities of platelets in coronary artery disease

Platelets have been implicated in the pathogenesis of coronary artery disease, and a number of studies have examined platelet function and coagulation parameters in such patients. We have examined platelet coagulant activities, volumes, and aggregate ratios in 23 patients with chest pain, seven of whom had normal coronary angiograms (group I) and 16 of whom had angiographically proven coronary artery disease (group II). There were no significant differences in the mean values for platelet volume or platelet aggregate ratios between the two groups. The platelet coagulant activities concerned with initiation and the early stages of intrinsic coagulation were significantly increased in patients in group II as compared with those in group I. No significant differences were noted between the two groups with respect to prothrombin time, partial thromboplastin time, and plasma levels of fibrinogen and coagulation factors V and VIII. However, the mean activity in plasma of antithrombin III (but not the level of antithrombin III antigen) was significantly lower in patients of group II compared with group I. Overall, our observations provide evidence for an enhanced contribution of platelets to the intrinsic coagulation system in patients with coronary artery disease. The platelet coagulant hyperactivity noted in these patients may reflect a role of platelets in the pathogenesis of coronary artery disease or may be secondary to the underlying arterial disease.

Platelet size in myocardial infarction

The mean platelet volume and platelet count were measured serially in 100 patients soon after myocardial infarction and again at a follow up clinic about seven weeks later. The results were compared with those in age matched controls. The mean platelet volume after infarction (mean 9.07 fl (SE 0.08] was significantly greater than in the controls (8.32 fl (SE 0.07); p less than 0.001), and was still raised at the follow up clinic (8.69 fl (SE 0.10); p less than 0.01). The mean platelet count on admission (275 X 10(9)/1 (SE 7] was significantly lower than in the control group (295 X 10(9)/1 (SE 5); p less than 0.05) and fell significantly during admission, with a mean change of -36 X 10(9)/1 (95% confidence limits -26, -45; p less than 0.01). At the follow up clinic the platelet count had risen to a level not significantly different from the admission value. As larger platelets are haemostatically more active, the finding of an increased mean platelet volume after myocardial infarction provides further evidence that abnormal platelet behaviour may be implicated in the process of infarction.

Experimental study of pulsatile and steady flow through a smooth tube and an atherosclerotic coronary artery casting of man

In vitro investigation of pulsatile and steady flows through a smooth, straight circular tube and a diseased human coronary artery cast was conducted with sugar-water solutions simulating the viscosity of blood. Time averaged pressure drops for pulsatile flows measured in the circular tube over a Reynolds number ranging from 50 to 1,000 were found to be identical to those for steady flows in the same tube, both of which were in excellent agreement with the Poiseuille flow prediction. For the polyurethane case (# 124) made from a human main coronary with significant but 'non obstructive' diffuse atherosclerotic disease, pressure drops for steady flows were found to be greater than Poiseuille flow predictions by a factor of 3-8 in the physiological Reynolds number range from about 100 to 400. Pulsatile flows in the same artery cast resulted in additional 30% increases in time averaged pressure drops, and thus flow resistance, compared to the steady flow data. Steady and pulsatile flow data measured in a straight, axisymmetric model of cast # 124 showed considerably smaller increases in flow resistance than those observed in # 124 casting.

In vivo platelet aggregation and plasma catecholamines in acute myocardial infarction

In vivo platelet aggregation assessed with the Filtragometer and potential correlates were compared among (1) patients with acute myocardial infarction (AMI), (2) normal controls, (3) patients with acute chest pain in whom AMI was eventually ruled out (ROMI), and (4) chronic outpatients (Cardiac Clinic group) with a history of myocardial infarction and/or angina pectoris. The measure was independent of sex, age, platelet count, immediate food intake, serum cholesterol, and triglyceride levels. The AMI group showed higher in vivo platelet aggregation than any of the other three groups (p less than 0.01). Least in vivo aggregation was seen in the normal group. Despite lack of correlation with the platelet aggregation measure, plasma epinephrine and norepinephrine showed statistically significant differences between the AMI and each of the other three groups. Our data support an association between platelet function and AMI, although not necessarily a cause and effect relationship.

Verapamil therapy for unstable angina pectoris: review of double-blind placebo-controlled randomized clinical trials

The effectiveness of verapamil in the management of patients with unstable angina pectoris associated with obstructive coronary artery disease was evaluated in 2 double-blind placebo-controlled randomized clinical trials. In the 1st study, verapamil was compared with placebo using alternating 48 hour treatment periods in a multiple cross-over protocol. Verapamil was superior to placebo in abolishing symptomatic and asymptomatic ischemic episodes; there were 127 ischemic events during treatment with placebo but only 27 episodes during therapy with verapamil (p less than 0.006). In the 2nd study, verapamil and placebo were compared using a double-blind randomized parallel design in which the choice of drug was altered and the doses administered were increased according to the individual responses. Verapamil reduced anginal attacks in 12 of 13 patients, but placebo was effective in only 1 of 6 (p less than 0.025); verapamil reduced daily anginal attacks from 3.2 to 0.6/day (p less than 0.01). Thus, verapamil is highly effective in the short-term management of patients with unstable angina secondary to coronary artery disease.

Arachidonic acid metabolites, hypertension and arteriosclerosis

The level of arterial blood pressure is set by complete interactions of several mechanisms which influence both blood flow in and resistance of the vascular system. An imbalance favouring elevation of vascular resistance or extracellular volume will result in hypertension. Such alterations may include increased activity of the sympathetic nervous system, of the renin-angiotensin system, or excessive secretion of mineralocorticoids. Of equal importance may be a reduced activity of blood pressure-lowering factors such as prostaglandins and the kallikrein-kinin system. This paper describes the possible significance of prostaglandins in the pathophysiology of hypertension and in degenerative vascular disease, based on their involvement in the control of vascular resistance, renal regulation of extracellular volume and platelet-vessel wall interactions. An abnormality in the biosyn-thesis of certain prostaglandin endoperoxide metabolites may lead to hypertension even without an increase in the activity of the classic blood-pressure-elevating systems. The contribution of prostaglandins for the development of hypertension and degenerative vascular disease may be based on an inherent abnormality of the prostaglandin system, as well as on the effects of major risk factors such as dietary intake of sodium and fat on prostaglandin synthesis. Specific blockade or stimulation of distinct biosynthetic pathways leading to antagonistically acting prostaglandins and nutritional manipulation of precursor fatty acids should lead to a better understanding of the pathomechanisms involved and may offer new strategies for therapy or prevention of these cardiovascular disorders.

Myocardial infarct extension: incidence and relationship to survival

Myocardial infarct extension, defined as reelevation or reappearance of creatine phosphokinase-MB (CK-MB) 48 hours after the onset of symptoms, was evaluated prospectively in 56 consecutive patients with acute myocardial infarction. Myocardial infarct extension occurred in eight patients (14%). The sensitivity, specificity and predictive accuracy in the diagnosis of myocardial infarct extension were 63%, 85% and 42%, respectively, for recurrent chest pain requiring morphine; 50%, 65% and 19% for recurrent ST-segment elevation on routine 12-lead ECGs; and 88%, 63% and 28% for reelevation of total CK. Three of the eight episodes of extension were clinically silent. Four of eight patients (50%) with extension died, compared with one of 46 patients (2%) without extension (p = 0.0009). CK-MB persisted for 72 hours or longer in 16 patients and identified seven of eight patients who subsequently had infarct extension. We conclude that myocardial infarct extension is an infrequent complication of acute myocardial infarction and is associated with a very high mortality rate. Persistence of CK-MB for 72 hours or more identifies a subgroup of patients at high risk for subsequent infarct extension and death.

Comparison of platelet function during exercise in normal subjects and coronary artery disease patients: Potential role of platelet activation in myocardial ischemia

Platelet function parameters as influenced by exercise stress were evaluated in 22 patients with coronary artery disease (CAD) and in 13 normal subjects. Upon exercise stress, 14 CAD patients exhibited positive tests and eight exhibited negative tests. Platelet counts during exercise increased similarly in normal and CAD patients. Platelet aggregation response to ADP was unaffected by exercise both in normal and CAD patients. Platelets from 7 of the 14 CAD patients with positive stress tests had increased sensitivity to endoperoxide analog (U-46619) defined as less than 200 ng/ml U-46619 required for 50% platelet aggregation. Resting plasma beta-thromboglobulin (B-TG) levels, an index of in vivo platelet activation, were significantly higher in CAD patients compared to normal subjects (74 +/- 7 and 41 +/- 5 ng/ml, respectively; p less than 0.02). During exercise plasma B-TG levels increased in normal subjects to 60 +/- 5 ng/ml. In contrast, B-TG levels increased to 102 +/- 14 ng/ml in CAD patients (p less than 0.01 compared to normal subjects). These increases were transient and B-TG declined to preexercise values soon after exercise. Eleven of the 12 CAD patients with positive exercise stress tests had increases in plasma B-TG levels, whereas only three of the eight CAD patients with negative stress tests had any increase. These observations of increased platelet activation in certain CAD patients during exercise may be related to exercise-induced myocardial ischemia.

Role of blood platelets and prostaglandins in coronary artery disease

In the last decade, several studies evaluating blood platelet function in patients with coronary heart disease have been reported. Although several platelet function abnormalities such as enhanced platelet aggregation, decreased platelet survival and increase in platelet release reaction in the stable condition and during stress in patients with myocardial ischemia have been recognized, the mechanism of these abnormalities is just beginning to be understood. Discovery of certain platelet and endothelium-generated prostaglandins has provided some information as to the possible mechanism of platelet dysfunction. Abnormalities of prostaglandin production and platelet sensitivity to various prostaglandins may have an important bearing on the enhanced platelet aggregation in vivo, genesis of atherosclerosis and probably precipitation of acute ischemic events. Since the discovery of these prostaglandins, the precise mode of action of several commonly used platelet-active drugs has been clarified. Development of new drugs acting at selective steps in the prostaglandin pathways may provide some exciting novel therapeutic procedures in patients with coronary heart disease.