Platelet hyperaggregability across the coronary bed in response to rapid atrial pacing in patients with stable coronary artery disease

Intense exercise at high altitude causes platelet loss across the brain in humans

Platelets are known primarily for their role in blood clotting; however, it is becoming clear that they play diverse roles beyond that of haemostasis. Exercise has been shown to activate platelets and stimulate neurogenesis, neuroplasticity and improve cognitive function, highlighting a potentially powerful link between platelet function and brain health. Despite this clear link between platelets and the brain, very little is known about the behaviour of platelets through the cerebral circulation in humans. We examined platelet concentration across the brain in exercising humans at sea level (340 m) and high altitude (6-8 days at 3800 m; a stimulus known to modify platelet function). During intense exercise at sea level, platelet concentration increased similarly by 27 ± 17% in the arterial and internal jugular venous circulations (exercise: P < 0.001, interaction: P = 0.262), indicating no uptake or release of platelets into/from the brain. At high altitude, resting platelet concentrations were similar to sea level values in both the arterial and jugular venous circulations (P = 0.590); however, intense exercise at high altitude caused a 31 ± 35% decrease in platelet concentration across the brain (P = 0.016). This divergent response across the brain was not observed in any other haematological or metabolic variables. These data highlight a unique situation where the combination of intense exercise and high altitude hypoxia cause a decrease in platelet concentration across the cerebral circulation. The physiological implications and mechanisms that might influence platelet function across the brain during exercise at high altitude remain to be established. KEY POINTS: Platelets are known primarily for their role in blood clotting; however, it is becoming clear that they play diverse roles beyond that of haemostasis. Exercise has been shown to activate platelets, which in turn stimulate neurogenesis, neuroplasticity and improve cognitive function, highlighting a powerful link between platelet function and brain health. At sea level, platelet concentration in blood going into and out of the brain was similar at rest, during maximal exercise and in recovery from exercise. During maximal exercise at high altitude, platelet concentration was 31% lower in the blood exiting the brain; the final destination of these platelets is unknown. The physiological implications and mechanisms that might influence platelet function across the cerebral circulation during exercise at high altitude remain to be established.

Evaluation of Whole-Blood Lumiaggregation

An evaluation of whole-blood lumiaggregation was conducted in a normal population. Platelet aggregation and adenosine triphosphate (ATP) secretion were monitored in a three-phase study that analyzed sample dilution, agonist dose response, and method comparison. In the first phase, the blood:saline ratio was varied; in the second phase, the concentration of the agonists was varied ; and in the last phase, a comparison of impedance aggregation and ATP release in whole blood to optical aggregation and ATP release in platelet-rich plasma (PRP) was performed. Five common platelet agonists— collagen, adenosine diphosphate (ADP), arachidonic acid, thrombin, and ristocetin—were used in this evaluation of the lumiaggregometer (Chrono-Log Corp., Havertown, PA, U.S.A.). The data revealed that the optimum blood:saline ratio for conducting platelet antigen studies is 1:1, although with some agonists other dilutions can be used. The agonist dose-response phase basically confirmed the manufacturer's concentration recommendations. Additionally, it was determined that platelet aggregation using the whole-blood impedance technique compared to the PRP optical method yielded similar information. Furthermore, the advantages of whole-blood impedance aggregation include its use in microsamples and more timely results due to minimal sample preparation. Key Words: Platelet aggregation—Lumiaggregation—Whole blood—Platelet-rich ptasma—ATP.

Approach to the Assessment of Platelet Function: Comparison between Optical-based Platelet-rich Plasma and Impedance-based Whole Blood Platelet Aggregation Methods

Platelet aggregation studies play an important role in the assessment of hereditary and acquired platelet function defects. The first aggregation test introduced into laboratory practice used platelet-rich plasma (PRP) where aggregation was detected by an optical method. The assessment of platelet function using whole blood (WB) aggregation by an impedance method followed up nearly 20 years later. The WB impedance aggregation assay appears to be superior to the optical method because it 1) evaluates platelets in a physiologic milieu in the presence of red and white blood cells, which are known to modulate platelet function; 2) is faster; 3) has higher sensitivity; and 4) does not require centrifugation, thus avoiding injury to platelets and loss of giant thrombocytes. These two assays were compared. Clearly, the WB impedance aggregation methodology has many advantages over the optical PRP assay for the assessment of the hyperactive platelet syndrome and the effects of anti-platelet drugs.

Platelet function in diabetic and nondiabetic patients with chronic obstructive pulmonary disease: a case control study

BACKGROUND

The effect of association between chronic obstructive pulmonary disease (COPD) and diabetes (DM) on platelet function has not been studied before.

OBJECTIVES

To evaluate the effect of the association between COPD and DM on platelet function and C reactive protein (CRP).

PATIENTS AND METHODS

This case control study was carried out on 110 stable COPD patients who were classified into diabetic and nondiabetic groups. In addition, 40 apparently healthy, age and sex-matched individuals were included in this study as a control group. Chest X-ray, pulmonary function testing and arterial blood gases were done for COPD patients. CRP and complete blood count (CBC) were measured in both patient and control groups.

RESULTS

Mean platelet volume (MPV), platelet distribution width (PDW), platelet crit (PCT) and CRP were significantly higher in COPD patients either nondiabetic or diabetic compared to control group. Moreover, MPV and CRP markers were significantly higher in COPD diabetic patients compared to nondiabetic. There was no significant difference in various laboratory data among different stages of COPD either diabetic or nondiabetic (P > 0.05). In COPD patients, MPV was a significantly positively correlated with CRP and PDW (r = 0.346, P < 0.001; r = 0.510, P < 0.001, respectively) and negatively correlated with PLT count (r = -0.294, P = 0.002).

CONCLUSION

MPV, PDW, PCT and CRP were significantly higher in COPD patients either nondiabetic or diabetic. Platelet function may be modified by the systemic inflammation that associated with COPD. Platelet activation as a prothrombotic sequence of this disease may be used as novel therapeutic target.

Improved myocardial perfusion in stable angina pectoris by oral lumbrokinase: a pilot study

OBJECTIVE

A novel antithrombotic agent, lumbrokinase, was evaluated in this pilot study for its efficacy in the treatment of symptomatic stable angina.

DESIGN

This was a single-armed cohort study.

SETTINGS

The study was conducted at the National Cardiovascular Center, Harapan Kita, Jakarta, Indonesia.

SUBJECTS

The study comprised 10 patients who had coronary artery disease and stable angina and who consented to the trial.

INTERVENTION

Patients were treated with oral lumbrokinase for 30 consecutive days in addition to their standard medical therapy.

OUTCOME MEASURES

Stress technetium-99m sestamibi myocardial perfusion imaging (MPI) was performed before and at the conclusion of the active treatment period. The degree and extent of inducible ischemia observed on the myocardial perfusion images were evaluated using the previously validated semiquantitative indices (Summed Stress Score and Summed Difference Score).

RESULTS

Following active treatment, the mean Summed Stress Score and Summed Difference Score deceased by 39% and 37%, respectively. The anginal symptom was ameliorated in 6 of 10 patients. No adverse reaction including major or minor bleeding was observed.

CONCLUSIONS

This paper represents the first description of the use of oral lumbrokinase in the treatment of chronic coronary artery disease with objective assessment using MPI. Oral lumbrokinase improves regional myocardial perfusion in patients with stable angina.

Platelet deposition in rabbit common carotid arteries promoted by arterial stenosisand spasm. A quantitative and morphological study

Coronary arteriograhy in patients with ischemic heart disease often shows spasm of the coronary arteries. The question is whether spasm is a triggering factor for thrombosis in a stenotic artery. If so, what are the mechanisms for this? A stenosing teflon ring was applied to the right common carotid artery of anesthetized rabbits and 1-nor-epinephrine was dripped over the outer surface of both carotid arteries, causing spasm. In control animals an indifferent solution did not cause spasm. Nineteen rabbits were killed 30 min or 24 h after treatment. Microscopically, arteries with stenosis and spasm contained thrombi nearby the stenosis significantly more often than arteries in control animals. In another 14 rabbits, killed at 30 min, the number of platelets on the intimal surface away from the stenosis was quantified. In arteries with both stenosis and spasm the counts were significantly greater than in arteries with no treatment. The intimal surface in stenotic and spastic arteries showed assumed imprints of eddying flow and endothelial injury downstream and upstream of the stenosis. Spastic arteries showed increased folding of the internal elastic membrane, altered endothelial cells, and adhering platelets. Spasm in a rabbit artery with a preformed stenosis facilitates thrombosis probably by creating increased flow disturbances. Spasm may induce endothelial injury, causing adherence of platelets.

Impaired tissue responsiveness to organic nitrates and nitric oxide: a new therapeutic frontier?

Nitric oxide (NO) is a physiologically important modulator of both vasomotor tone and platelet aggregability. These effects of NO are predominantly mediated by cyclic guanosine-3,'5'-monophosphate (cGMP) via activation of soluble guanylate cyclase. However, in patients with ischemic heart disease, platelets and coronary/peripheral arteries are hyporesponsive to the antiaggregatory and vasodilator effects of NO donors. NO resistance is also associated with a number of coronary risk factors and presents in different disease states. It correlates with conventional measures of "endothelial dysfunction," and represents a multifaceted disorder, in which smooth muscle and platelet NO resistance are equally important, as sites of abnormal NO-driven physiology. NO resistance results largely from a combination of "scavenging" of NO by superoxide anion radical (O(2)(-)) and of (reversible) inactivation of soluble guanylate cyclase. It constitutes an impaired physiological response to endogenous NO (endothelium-derived relaxing factor, EDRF) and, as such, may contribute to the increased risk of ischemic events. Impairment in responsiveness to NO in ischemic patients implies a potential problem that those patients, in greatest need of nitrate therapy, may be least likely to respond. The prognostic impact of NO resistance at vascular and platelet levels has been demonstrated in patients with ischemic heart disease, and it has been shown that a number of agents (angiotensin-converting enzyme [ACE] inhibitors, perhexiline, insulin, and possibly statins) ameliorate this anomaly. The current review examines different aspects of the "NO resistance" phenomenon and discusses some related methodological issues.

Mean platelet volume and exercise stress test

BACKGROUND

Long-term moderate or strenuous physical activity is associated with a considerable reduction in cardiovascular morbidity and mortality. However acute exercise leads to a transient activation of the thrombotic system. Healthy individuals can react this by increasing their fibrinolytic capacity acutely. However, patients with ischemic heart disease, lacking fibrinolytic potential, may be at considerable risk for acute ischemic events if exposed to heavy physical exertion. Platelet size has been shown to reflect platelet activity. The mean platelet volume (MPV) can reflect changes in either the level of platelet stimulation or rate of platelet production.

DESIGN AND METHODS

We evaluated Treadmill exercise test (TMET) and compared MPV values (fl) before and after TMET in 63 consecutive patients who, then, underwent coronary angiography and found to have significant coronary artery disease in more than one coronary artery (>70% diameter stenosis in left anterior descending, right coronary or circumflex artery and >50% diameter stenosis in left main coronary artery). Sixty-three male patients were enrolled as a patient group with a mean age of 52.43 +/- 4.08 years and with strongly positive exercise test (> or =2 mm ST segment depression, horizontal or down-sloping). Thirty-five patients without significant coronary artery disease were selected as a control group with a mean age of 52.66 +/- 4.39 years having undergone TMET.

RESULTS AND DISCUSSION

In the patient and control groups, mean MPV values before TMET were the same, 8.52 +/- 0.63 and 8.45 +/- 0.58 respectively. Following TMET within 30 minutes, mean MPV were 10.03 +/- 0.96 and 8.50 +/- 0.45 respectively ( p < 0.001). When pre and post-TMET MPV values were evaluated together, the patient group had a significant increase in the MPV ( p < 0.001), whereas, the control group had no significant increase in the MPV ( p = 0.379). It was concluded that exercise possibly makes patients with significant coronary artery disease, more susceptible to a thrombotic event through various routes, one of that is platelet activation that could be measured indirectly via MPV. Healthy subjects react this thrombotic process by increasing their fibrinolytic capacity acutely. Patients with ischemic heart disease, particularly those with significantly narrowed coronary arteries, known to lack fibrinolytic capacity and have high shear stress, on the other hand, might face ischemic events, including sudden death following acute exercise.

Serotonin aggravates exercise-induced cardiac ischemia in the dog: effect of serotonin receptor antagonists

We investigated the effects of serotonin (5-HT), SL65.0472 (7-fluoro-2-oxo-4-[2-[4-thieno[3,2-c]pyridine-4-yl)piperazin-1-yl]ethyl]-1,2-dihydroquinoline-1-acetamide, a 5-HT(1B)/5-HT(2A) receptor antagonist) and ketanserin (a 5-HT(2A) receptor antagonist) during exercise-induced cardiac ischemia in conscious dogs. Dogs were administered a hypercholesterolemic diet and an inhibitor of nitric oxide synthetase to produce chronic endothelial dysfunction. Myocardial ischemia was induced by a treadmill exercise test associated with limitation of left anterior descending coronary blood flow. Infusion of serotonin during exercise produced dose-related cardiovascular changes (after 10 microg/kg/min; heart rate +27+/-6 bpm, systolic blood pressure +18+/-3 mm Hg, left circumflex coronary blood flow +64+/-8 ml/min, myocardial segment length shortening in the ischemic zone -5.9+/-1.9%, P<0.05). SL65.0472 blocked serotonin-induced increases in blood pressure, rate pressure product and circumflex coronary artery flow (100 microg/kg i.v., P<0.05) and reduced serotonin-induced ischemic myocardial segment length shortening (300 microg/kg i.v., P<0.05). Ketanserin (30-300 microg/kg i.v.) had no significant effect on any serotonin-induced changes during exercise. Thus, SL65.0472 opposes serotonin-induced myocardial dysfunction in a dog model of exercise-induced ischemia.

Effects of L-arginine on flow mediated dilatation induced by atrial pacing in diseased epicardial coronary arteries

OBJECTIVE

To examine the effects of L-arginine on basal coronary tone and flow mediated dilatation induced by atrial pacing in patients with coronary artery disease and stable angina.

DESIGN

Atrial pacing was performed during intracoronary infusions of normal saline and L-arginine (150 micromol/min) in 8 patients with coronary artery disease and stable angina. The luminal diameter of epicardial coronary arteries was assessed by quantitative angiography.

RESULTS

L-arginine administration significantly increased the diameter of all the coronary segments and stenoses. During atrial pacing with saline infusion, luminal diameter of the proximal, distal, and stenosis reference segments increased significantly (p < 0.01 versus saline) but stenosis diameter did not change. L-arginine administration did not change the magnitude (NS) of atrial pacing induced dilatation in proximal and distal segments and in coronary stenoses and their reference segments.

CONCLUSIONS

Non-stenotic segments of diseased coronary arteries dilate in response to atrial pacing but stenoses do not. L-arginine dilates coronary segments and stenoses but does not increase the magnitude of the response to atrial pacing in proximal and distal segments and in coronary stenoses and their reference segments. These findings provide evidence that the shear stress responsive mechanism is absent at stenoses but present in non-stenotic segments of diseased coronary arteries. They also indicate a relative deficiency of L-arginine, except in the shear response mechanism.

Modulation of beta-adrenergic receptor subtype activities in perioperative medicine: mechanisms and sites of action

This review focuses on the mechanisms and sites of action underlying beta-adrenergic antagonism in perioperative medicine. A large body of knowledge has recently emerged from basic and clinical research concerning the mechanisms of the life-saving effects of beta-adrenergic antagonists (beta-AAs) in high-risk cardiac patients. This article re-emphasizes the mechanisms underlying beta-adrenergic antagonism and also illuminates novel rationales behind the use of perioperative beta-AAs from a biological point of view. Particularly, it delineates new concepts of beta-adrenergic signal transduction emerging from transgenic animal models. The role of the different characteristics of various beta-AAs is discussed, and evidence will be presented for the selection of one specific agent over another on the basis of individual drug profiles in defined clinical situations. The salutary effects of beta-AAs on the cardiovascular system will be described at the cellular and molecular levels. Beta-AAs exhibit many effects beyond a reduction in heart rate, which are less known by perioperative physicians but equally desirable in the perioperative care of high-risk cardiac patients. These include effects on core components of an anaesthetic regimen, such as analgesia, hypnosis, and memory function. Despite overwhelming evidence of benefit, beta-AAs are currently under-utilized in the perioperative period because of concerns of potential adverse effects and toxicity. The effects of acute administration of beta-AAs on cardiac function in the compromised patient and strategies to counteract potential adverse effects will be discussed in detail. This may help to overcome barriers to the initiation of perioperative treatment with beta-AAs in a larger number of high-risk cardiac patients undergoing surgery.

Enhanced platelet aggregation in the coronary circulation after coronary spasm

A recently developed platelet aggregometer using a laser light scattering method is capable of monitoring the increase in size of small-sized platelet aggregates (diameter 9-25 microm), which cannot be detected with the conventional methods. Whether coronary spasm can cause platelet aggregation in the coronary circulation is unknown. We investigated platelet aggregation, especially small-sized platelet aggregates, simultaneously in the coronary sinus and the aortic root in 18 patients with coronary spastic angina before and after a left coronary artery spasm induced by intracoronary injection of acetylcholine, and in 15 patients with stable exertional angina before and after acute myocardial ischemia induced by rapid right atrial pacing. Platelet aggregation in 12 patients with chest pain syndrome was also examined before and after coronary spasms provoked by acetylcholine. The number of small-sized platelet aggregates increased significantly in the coronary sinus [2.0+/-0.6 x 104 to 4.1+/-1.0 x 104 (V), P<.01] and in the aortic root [1.7+/-0.6 x 104 to 3.2+/-0.6 x 104 (V), P<.05], and the coronary sinus-arterial difference in the number of small-sized platelet aggregates [2.3+/-1.9 x 103 to 1.1+/-0.4 x 104 (V), P<.01] increased significantly after attacks in the coronary spastic angina group, but remained the same in the stable exertional angina group after attacks and in the chest pain syndrome group after the administration of acetylcholine. Therefore, we can conclude that acute myocardial ischemia induced by coronary spasm causes platelet aggregation in the coronary circulation.

Stable angina and acute coronary syndromes are associated with nitric oxide resistance in platelets

OBJECTIVES

The study examined possible clinical determinants of platelet resistance to nitric oxide (NO) donors in patients with stable angina pectoris (SAP) and acute coronary syndromes (ACS), relative to nonischemic patients and normal subjects.

BACKGROUND

We have shown previously that platelets from patients with SAP are resistant to the antiaggregating effects of nitroglycerin (NTG) and sodium nitroprusside (SNP).

METHODS

Extent of adenosine diphosphate (1 micromol/liter)-induced platelet aggregation (impedance aggregometry in whole blood) and inhibition of aggregation by NTG (100 micromol/liter) and SNP (10 micromol/liter) were compared in normal subjects (n = 43), nonischemic patients (those with chest pain but no fixed coronary disease, (n = 35) and patients with SAP (n = 82) or ACS (n = 153). Association of NO resistance with coronary risk factors, coronary artery disease (CAD), intensity of angina and current medication was examined by univariate and multivariate analyses.

RESULTS

In patients with SAP and ACS as distinct from nonischemic patients and normal subjects, platelet aggregability was increased (both p < 0.01), and inhibition of aggregation by NTG and SNP was decreased (both p < 0.01). Multivariate analysis revealed that NO resistance occurred significantly more frequently with ACS than with SAP (odds ratio [OR] 2.3:1), and was less common among patients treated with perhexiline (OR 0.3:1) or statins (OR 0.45:1). Therapy with other antianginal drugs, extent of CAD, intensity of angina and coronary risk factors were not associated with variability in platelet responsiveness to NO donor.

CONCLUSIONS

Patients with symptomatic ischemic heart disease, especially ACS, exhibit increased platelet aggregability and decreased platelet responsiveness to the antiaggregatory effects of NO donors. The extent of NO resistance in platelets is not correlated with coronary risk factors. Pharmacotherapy with perhexiline and/or statins may improve platelet responsiveness to NO.

Platelet inhibitory effect of nitric oxide in the human coronary circulation: impact of endothelial dysfunction

OBJECTIVES

We sought to determine whether coronary vascular nitric oxide (NO) release in vivo modulates platelet activation.

BACKGROUND

Nitric oxide modulates vasodilator tone and platelet activity via the cyclic guanosine monophosphate (cGMP) pathway, but whether coronary endothelial dysfunction influences platelet activation in humans is unknown.

METHODS

In 26 patients, we measured coronary blood flow, epicardial diameter and coronary sinus platelet cGMP content during intracoronary infusions of acetylcholine (ACH), L-NG monomethyl arginine (L-NMMA) and sodium nitroprusside.

RESULTS

Acetylcholine increased platelet cGMP content (p = 0.013), but its magnitude was lower in patients with endothelial dysfunction; thus, patients with epicardial constriction with ACH had a 7 +/- 6%, p = ns change compared with a 32 +/- 13%, p = 0.05 increase in platelet cGMP in those with epicardial dilation. Similarly, patients with atherosclerosis or its risk factors had a smaller increase (9 +/- 6%) compared with those having normal coronary arteries without risk factors (51 +/- 22%, p = 0.019). L-NG monomethyl arginine decreased platelet cGMP content to a greater extent in patients with epicardial dilation with ACH (- 15 +/- 7%, p = 0.06) compared to those with constriction (+5 +/- 6% change, p = 0.5). Sodium nitroprusside produced a similar increase in platelet cGMP content in patients with and without endothelial dysfunction (p = 0.56). The effects of sodium nitroprusside, but not ACH or L-NMMA, were reproduced in vitro.

CONCLUSIONS

Platelet cGMP levels can be modulated by basal and stimulated release of NO. The platelet inhibitory effect of NO is reduced in patients with endothelial dysfunction, which may explain their increased risk from thrombotic events and the improved survival associated with strategies designed to improve vascular function.

Low-grade exercise enhances platelet aggregability in patients with obstructive coronary disease independently of myocardial ischemia

Moderate and strenuous exercise is known to enhance platelet aggregability in patients with obstructive coronary artery disease (CAD), but the effect of low-grade exercise is not known. We assessed shear-induced platelet aggregability before and after mild exercise (less than or equal to stage III of the modified Bruce protocol) in 27 patients with documented CAD who were receiving aspirin and in 12 subjects without CAD (controls). Ex vivo platelet aggregability was assessed in flowing whole blood as the time to occlude a collagen and adenosine diphosphate-coated ring; shorter times indicated greater aggregability. Aggregability, plasma von Willebrand factor (vWF) antigen, platelet and white cell counts, and hematocrit were measured at baseline, immediately after exercise (peak), and at 30 and 180 minutes after exercise. Exercise of similar workloads induced myocardial ischemia in 14 patients (group 1), but not in the other 13 (group 2) nor in controls. Both patient groups showed a reduction in aggregation time at peak exercise compared with baseline (group 1: 84+/-17 seconds at peak vs 96+/-22 seconds at baseline; group 2: 84+/-20 seconds at peak vs 99+/-20 seconds at baseline; p <0.03 for both comparisons), with a return to baseline values within 180 minutes. No significant variation occurred in controls (89+/-18 seconds at peak vs 85+/-21 second at baseline). Changes in vWF antigen did not differ significantly among groups. Aggregation times did not correlate with hematocrit or platelet and white cell counts. Thus, even low-grade exercise transiently enhances whole blood platelet aggregability in patients with obstructive CAD, but not in controls. The effect is independent of myocardial ischemia, occurs despite aspirin, and is likely dependent on hemodynamic factors interacting with coronary obstructions or dysfunctional endothelium.

Exercise shifts the platelet aggregation modulatory role from native to mildly oxidized low-density lipoprotein

PURPOSE

The role of low-density lipoprotein (LDL) lipid peroxides in strenuous exercise-induced changes in platelet function was studied in 30 patients (male/female = 22/8) aged 30-62 yr (mean +/- SD = 508).

METHODS

All subjects were subjected to a treadmill exercise test, using the standard Bruce protocol. Blood samples were collected pre-, peak, and 10 min postexercise to assess hematological and biochemical parameters and platelet aggregation. Ex vivo whole blood platelet aggregation during treadmill exercise was assessed in 10 subjects by adding mildly oxidized LDL.

RESULTS

Preexercise, a correlation existed between plasma thromboxane (TX) levels and plasma LDL cholesterol or beta-thromboglobulin (beta-TG) levels (r = 0.48, P < 0.05: r = 0.47, P < 0.05, respectively), whereas, at peak exercise, TX and beta-TG levels increased, but no correlation was seen. At peak exercise, platelets showed hyperaggregability in terms of maximal amplitude and reaction slope (P < 0.001 and P < 0.01, respectively). In contrast to the increase in plasma lipid peroxide levels seen during peak exercise (P < 0.05), LDL lipid peroxides decreased during exercise, this decrease reaching a statistical significance at 10 min postexercise (P < 0.05). In addition, the ex vivo addition of mildly oxidized LDL (10 mg protein x L(-1)) to peak exercise blood resulted in a significant attenuation of platelet aggregation and a decrease in TX release. At 10 min postexercise, a correlation was seen between LDL lipid peroxides and TX levels (r = 0.78, P < 0.001) or beta-TG levels (r = 0.68, P < 0.005).

CONCLUSION

These results suggest that LDL lipid peroxides play a role in modulating and attenuating platelet aggregation during strenuous exercise.

Soluble L-selectin and neutrophil derived oxidative stress after pacing induced myocardial ischemia in chronic stable coronary artery disease

We studied the effect of atrial pacing induced myocardial ischemia on levels of soluble L-selectin (sL-selectin) and generation of neutrophil derived reactive oxygen species (ROS) in 10 patients with coronary artery disease (CAD) and stable angina and in six individuals without CAD. Myocardial ischemia was measured metabolically by lactate sampling from the coronary sinus (CS) and arterial blood at each pacing step. Before each pacing step, at peak pacing and shortly after cessation, plasma concentrations of sL-selectin and generation of ROS using the chemiluminescence method were measured in CS and femoral artery blood. Baseline sL-selectin levels in CS samples were significantly lower in the CAD compared to the control group (547 +/- 80 vs 836 +/- 82 ng/mL, P = 0.03). At peak pacing, nine of ten patients with CAD developed myocardial ischemia (lactate extraction ratio at rest 28% +/- 7%, at peak pacing -16% +/- 6%). In these patients, luminol-enhanced chemiluminescence (CL, 0.88 +/- 0.45 vs 1.9 +/- 0.9 cpm x 10(5), P = 0.09) and levels of sL-selectin (547 +/- 80 vs 764 +/- 86 ng/mL, P = 0.03) from naive neutrophils increased significantly in CS blood suggesting a potent in vivo activation of neutrophils. In control patients, incremental pacing caused neither myocardial ischemia nor a significant change of chemiluminescence or of sL-selectin levels. In conclusion, myocardial ischemia induced by pacing tachycardia is able to activate neutrophils in patients with chronic stable coronary artery disease leading to increased generation of ROS and shedding of L-selectin into the coronary circulation.

Effect of systemic alpha-2 adrenergic blockade on the morning increase in platelet aggregation in normal subjects

To assess whether activation of platelets by catecholamines contributes to the increase in platelet aggregation associated with either the assumption of upright posture or exercise, we studied the effect of oral yohimbine on these phenomena. Whole blood platelet aggregation and plasma catecholamine levels were measured before and after standing and at peak exercise in untreated normal subjects and after oral yohimbine. Neurochemical indexes indicated systemic alpha2-receptor blockade by yohimbine. Yohimbine reduced the orthostatic increase in platelet aggregation response by 63+/-11%, but exercise-induced increase in aggregation was unaffected. Thus, alpha2-adrenergic blockade attenuates the orthostatic increase in platelet aggregation. Agents designed to inhibit the morning surge in catecholamine levels or block platelet alpha2 adrenoceptors may reduce the risk of thrombotic vascular events in atherosclerosis.

Dual effects of nimesulide, a COX-2 inhibitor, in human platelets

Nimesulide (CAS 51803-78-2) has been shown to exert marked anti-inflammatory effect in several in vivo models of inflammation. Since nimesulide is considered to be a selective inhibitor of COX-2, it has not been studied in detail in relation to its mechanistic effects on platelets, which express COX-1. This study was conducted to investigate the effects of nimesulide in platelet aggregation. We show that nimesulide (1-100 microM) inhibited platelet aggregation induced by adrenaline (20-200 microM). It also inhibited thromboxane A2 (TXA2) formation by platelets at low concentration (IC50; 1 microM). However, much lower concentrations of nimesulide (0.01-0.1 microM) potentiated the aggregatory response of subthreshold concentrations of adrenaline (0.2-2 microM). Such an effect was blocked by Ca2+-channel blockers, verapamil and diltiazem (IC50: 7 and 46 microM, respectively), nitric oxide donor, SNAP (IC50; 2 microM) and cinchonine (10 nM) but not by genistein (up to 10 microM). These results are indicative of the concentration-dependent dual effects of nimesulide on human platelet aggregation. The synergistic effect of low doses of nimesulide and adrenaline seems to be mediated through inhibition of multiple signalling pathways.

Analysis of low-speed rotational atherectomy for the reduction of platelet aggregation

Platelet activation is an important determinant of acute outcomes of percutaneous intervention. The objective of this study was to assess the effect of rotational atherectomy on platelet activation in an in vitro model. Freshly collected heparinized porcine blood was exposed to a 2.0-mm Rotablator burr rotating at one of three speeds: 180,000, 140,000, or 0 rpm. The specimens were analyzed immediately for concentration and size of platelet aggregates and plasma-free hemoglobin. There were significantly more platelet aggregates of >20-microm diameter at higher speeds (7,434+/-2,193 at 180,000, vs. 2,269+/-627 at 140,000, vs. 633+/-258 aggregates/ml at 0 rpm; P < 0.001). Plasma-free hemoglobin, a simple measure of cell damage, decreased with decreasing rotational speed (429+/-168 mg/dl at 180,000, vs. 88+/-44 mg/dl at 140,000, vs. 9+/-9 mg/dl at 0 rpm; P < 0.0001). In vitro, platelet activation decreases with decreasing burr speed, suggesting that the use of the Rotablator system at its minimum approved speed (140,000 rpm) could prove clinically beneficial.

Neutrophil-derived oxidative stress after myocardial ischemia induced by incremental atrial pacing

We studied the effect of atrial pacing-induced myocardial ischemia on the generation of oxygen free radicals (OFR) in 8 patients with verified coronary artery disease (CAD) and in a control group of 4 patients without coronary atherosclerosis. Myocardial ischemia was measured metabolically by simultaneous lactate sampling from coronary sinus (CS) and arterial blood. Generation of OFR from purified viable polymorphonuclear neutrophils (PMN) was assessed by means of the chemiluminescence (CL) method. At peak pacing, 7 of 8 patients with CAD exhibited transient myocardial ischemia (mean lactate extraction ratio at rest: 23.6 +/- 7.7 vs 5.21 +/- 5.1% at peak pacing, p = 0.012). In these patients, unstimulated PMN harvested from the CS depicted a significant increase of luminol-enhanced CL (from 1.06 +/- 0.54 to 2.15 +/- 1.28 cpm x 10(5), p = 0.012) after atrial pacing. There was no additional effect from further ex vivo stimulation with phorbol myristate acetate. This finding underscores the role of myocardial ischemia as a potent endogenous activator of PMN function and may have implications in the pathogenesis and progression of atherosclerosis.

Basal and flow-mediated nitric oxide production by atheromatous coronary arteries

OBJECTIVES

This study assessed the effects of inhibition of nitric oxide synthesis on epicardial human coronary arteries and on coronary flow velocity during baseline conditions and during atrial pacing.

BACKGROUND

Epicardial coronary artery dilation occurs in response to an increase in heart rate. It is not known whether the dilation of both angiographically normal and diseased epicardial coronary arteries during atrial pacing is nitric oxide dependent in humans.

METHODS

The effects of an intracoronary infusion (4 mumol/min for 8 min) of NG-monomethyl-L-arginine (LNMMA), an inhibitor of nitric oxide synthesis, was studied in 16 patients with coronary artery disease and in 6 patients with normal coronary arteriograms. In all patients atrial pacing was performed during normal saline and during LNMMA infusion. the lumen diameter of epicardial coronary arteries was assessed by quantitative angiography, and changes in blood flow velocity were measured with a Doppler catheter.

RESULTS

During saline infusion a significant increase in the lumen diameter of the proximal (p < 0.05) and distal (p < 0.01) segments of both normal and diseased arteries occurred during atrial pacing. No significant lumen diameter changes occurred in either group when atrial pacing was performed during LNMMA infusion. Stenosis diameter decreased during LNMMA infusion but did not change with atrial pacing either during saline infusion or during LNMMA infusion. The mean percent change in coronary blood flow with atrial pacing was less (p < 0.05) during LNMMA infusion than during saline infusion in both groups.

CONCLUSIONS

These findings confirm that epicardial coronary artery dilation induced by pacing is nitric oxide dependent. Nitric oxide production contributes to the vasomotor tone of coronary resistance vessels. Nitric oxide is produced at the site of atheromatous stenosis but is unaffected by pacing.

Dietary L-arginine supplementation normalizes platelet aggregation in hypercholesterolemic humans

OBJECTIVES

The present study was designed to test the hypothesis that long-term dietary supplementation with the nitric oxide precursor L-arginine would enhance vascular or platelet-derived nitric oxide activity, or both, and thereby inhibit platelet reactivity in hypercholesterolemic humans.

BACKGROUND

We have shown that reduced vascular activity of nitric oxide in hypercholesterolemic rabbits can be restored by L-arginine supplementation. The improvement in nitric oxide activity is associated with an inhibition of platelet aggregation ex vivo. This effect is most likely due to increased elaboration of endothelium- or platelet-derived nitric oxide, or both, because the inhibition of platelet reactivity was associated with elevation of intraplatelet cyclic guanosine monophosphate and was reversed by the nitric oxide synthase antagonist N-methyl-arginine.

METHODS

In a double-blinded, randomized, placebo-controlled trial, hypercholesterolemic patients were assigned to L-arginine hydrochloride, 8.4 g/day orally, or placebo for 2 weeks. Platelet-rich plasma was obtained for aggregometry induced by collagen (1 to 10 micrograms/ml) at four points: baseline, after 2 weeks of treatment, after a 2-week washout and after a long-term washout of 16 weeks on average. Aggregation was quantified by light transmittance and expressed as a percent transmittance observed with platelet-poor plasma.

RESULTS

Compared with normocholesterolemic control subjects, platelets from hypercholesterolemic subjects stimulated with 5 micrograms/ml of collagen showed increased aggregability (68.6% in hypercholesterolemic patients vs. 54.5% in normocholesterolemic control subjects, p < or = 0.02). After 2 weeks of treatment with L-arginine (but not placebo), platelet reactivity was modestly reduced; this effect persisted for 2 weeks after discontinuation of arginine (52.6% in arginine-treated patients vs. 65.1% in normocholesterolemic control subjects, p = 0.07). After 18 weeks (i.e., 16 weeks after discontinuing arginine treatment), the platelets of hypercholesterolemic patients once again became hyperaggregable, and the extent of platelet aggregation was significantly increased compared with the 4-week point (73.6% after vs. 52.6% during arginine treatment, p < 0.01). No significant change in platelet reactivity was seen in placebo-treated hypercholesterolemic patients throughout the study. L-Arginine treatment was well tolerated without side effects.

CONCLUSIONS

This double-blinded, placebo-controlled study demonstrates that dietary supplementation with L-arginine can modestly attenuate the increased platelet reactivity seen in hypercholesterolemic patients. The data are consistent with our previous studies in hypercholesterolemic animals, demonstrating that L-arginine restores endogenous nitric oxide activity and inhibits platelet aggregation. Enhancement of endogenous nitric oxide activity is a potential novel therapeutic strategy worthy of further study.

Suppressed anti-aggregating and cGMP-elevating effects of sodium nitroprusside in platelets from patients with stable angina pectoris

Platelet hyperactivity plays an important role in the pathogenesis of cardio-vascular diseases. In patients with stable angina pectoris, we have recently demonstrated that nitroglycerin suppressed the increased platelet aggregability. The anti-aggregating effect of NTG and other nitrovasodilators is mediated by platelet guanylate cyclase, which generates cyclic GMP (cGMP) in response to nitric oxide (NO) liberated from the nitrovasodilator molecule. In the current study we utilised a more "direct" NO donor, sodium nitroprusside (SNP), to examine reversal of ADP-induced platelet aggregation in comparison with intraplatelet cGMP elevation in platelets from normal subjects (n = 22) and patients with stable angina pectoris (n = 23). Concentrations of SNP associated with 50% reversal of aggregation were 2.7 +/- 0.4 x 10(-7) mol/L with normal subjects and 4.5 +/- 0.5 x 10(-6) mol/L with patients (P < 0.01). SNP produced a concentration-dependent elevation of intraplatelet cGMP content: with 10(-4) mol/L SNP this was 17-fold for normals and 5-fold for patients (P < 0.01). An increase in cAMP content was seen only with 10(-4) mol/L SNP, and was 157 +/- 11% of baseline in platelets from normal subjects and 138 +/- 14% in patients. There was a strong interrelationship between cGMP-stimulating and anti-aggregating effects of SNP. The decrease in cGMP responsiveness to SNP was not related to a dysfunction of platelet guanylate cyclase; neither basal nor SNP-stimulated activity of the enzyme varied significantly between normal subjects and patients. Lipophilic derivatives of cGMP (db-cGMP) and cAMP (db-cAMP) caused reversal of aggregation; there was a nonsignificant trend towards decreased responsiveness of platelets from patients to both db-cGMP and db-cAMP. The observed decrease in responsiveness of platelets from angina patients to anti-aggregating effects of the exogenous NO donor, SNP, can therefore be attributed to suppressed cGMP accumulation. These results imply reduced platelet sensitivity to endogenous NO (endothelium-derived relaxing factor): this might contribute to platelet hyperaggregability observed in angina pectoris.

N-Acetylcysteine potentiates nitroglycerin-induced reversal of platelet aggregation

N-Acetylcysteine (N-AC) potentiates the systemic and coronary hemodynamic and antianginal effects of nitroglycerin (NGT) in humans; NTG/N-AC reduces the incidence of acute myocardial infarction in patients with unstable angina pectoris. Although previous studies have demonstrated that NTG exerts antiaggregatory effects on platelets, little information is available concerning the possible potentiation by N-AC of NTG antiplatelet effects. In the present study, we examined the in vitro effects of NTG and the combination of NTG with N-AC on reversal of ADP-induced aggregation in platelet-rich plasma (PRP) obtained from normal subjects and patients with stable angina pectoris. We also examined the potential effect of background aspirin therapy on this interaction. NTG, added to platelets 0.5 min after the beginning of aggregation, suppressed the incipient aggregation and provoked the appearance of a disaggregation phase, resulting in a concentration-dependent reversal of platelet aggregation. Platelet responsiveness to NTG was significantly less (p < 0.01) in both groups of patients (receiving and not receiving aspirin) as compared with normal subjects. N-AC (10(-5) M), which did not in itself affect aggregation, induced a threefold potentiation (p < 0.05) of the antiaggregating effect of NTG that was similar in degree for all tested groups of individuals. This potentiation of the antiplatelet effects of NTG by N-AC may contribute to the efficacy of combined NTG/N-AC therapy in patients with acute ischemic syndromes.

Inhibitory effect of nitroglycerin and sodium nitroprusside on platelet activation across the coronary circulation in stable angina pectoris

This study assessed the inhibitory effect of nitroglycerin and sodium nitroprusside on platelet aggregation in a model of platelet activation across coronary circulation. Platelet aggregation is believed to contribute to the precipitation of acute ischemic syndromes. We previously showed that rapid atrial pacing in patients with stable coronary artery disease (CAD) causes platelet hyperaggregability during blood passage in coronary circulation. Because nitroglycerin and sodium nitroprusside have been shown to inhibit platelet aggregation, we examined the effect of these drugs on this model of platelet activation. During catheterization of 19 patients with CAD (> 50% diameter narrowing of epicardial coronary arteries), we measured platelet aggregation (using whole blood platelet aggregometry) on blood samples obtained simultaneously from the coronary sinus and aorta at rest, and 2 minutes after onset of rapid atrial pacing. This procedure was repeated during an intravenous infusion of either nitroglycerin (n = 9) or sodium nitroprusside (n = 10). There was no arteriovenous difference in platelet aggregation under resting conditions. Atrial pacing caused an increase in platelet aggregation in coronary sinus blood (+64 +/- 9%; p < 0.01), but not in arterial blood (15 +/- 12% decrease; p = NS). This increase was transient and returned toward baseline 10 minutes after termination of pacing. Although resting platelet aggregation was not affected by nitroglycerin or sodium nitroprusside, activation of platelets with atrial pacing across the coronary bed was stopped by pretreatment with therapeutic doses of nitroglycerin or sodium nitroprusside. When coronary blood flow increases in patients with CAD, platelets are activated and aggregate more easily. This activation can be blunted by pretreatment with nitroglycerin or sodium nitroprusside.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous platelet aggregation in whole blood is increased in non-insulin-dependent diabetes mellitus and in female but not male patients with primary dyslipidemia

Increased platelet aggregability has been shown in hypercholesterolemia, and stirring-induced spontaneous aggregation in whole blood is increased in insulin-dependent diabetes mellitus (DM). We have determined spontaneous aggregation in citrated (10 mM) whole blood, from 27 primary dyslipidemic patients (DYS; 14F, 13M), 16 male non-insulin-dependent DM (NIDDM) patients, and 17 normolipidemic controls (N; 6F, 11M), using platelet counting to quantify aggregation. Spontaneous aggregation was significantly higher, both in the female DYS group (median 30% [interquartile range 25,50], P < 0.005) and the NIDDM group (33% [25,41], P < 0.005), than in the N group (17% [12,27]), but did not differ significantly in the male DYS group (23% [10,33]). Similar results were obtained in the presence of indomethacin (25 mumol/l) to prevent artefactual thromboxane (TX) A2 formation, indicating that increased spontaneous aggregation was TXA2-independent. Interestingly, increased spontaneous aggregation appeared to be independent of serum cholesterol and triglyceride concentrations, as well as age and sex per se. We conclude that spontaneous platelet aggregation was increased both in female primary dyslipidemic patients and NIDDM patients, but not in male DYS patients. The clinical significance of increased spontaneous platelet aggregability is that it may favour shear-induced aggregation which may occur at critical arterial stenoses in vivo leading to thrombus formation.

Eicosanoid biosynthesis in patients with stable angina: beneficial effects of very low dose aspirin

OBJECTIVE

We assessed the production of eicosanoids and the effects of very low dose aspirin in patients with stable angina under basal conditions and during rapid atrial pacing.

BACKGROUND

Platelet activation occurs in acute ischemic syndromes but is still controversial in stable angina. Very low dose aspirin is known to be platelet selective and can be used to test the hypothesis of the platelet origin of increased thromboxane production in stable angina.

METHODS

Urinary excretion of eicosanoids was measured in 42 patients, including 24 patients with and 18 patients without coronary artery disease. The effects of 50 mg/day of aspirin were measured at rest and during pacing-induced ischemia in 10 patients with stable angina and were compared with a similar group of patients not treated by aspirin.

RESULTS

Excretion of 11-dehydro-thromboxane B2 was 2.6 times higher in patients with stable angina than in healthy subjects (mean [+/- SEM] 74.8 +/- 13.0 [24 patients] vs. 29.0 +/- 5.4 [18 patients] ng/mmol of creatinine, p < 0.01). Urinary prostacyclin metabolite levels did not differ between the two groups. Treatment for 8 days with 50 mg/day of aspirin inhibited platelet cyclooxygenase, as reflected by the 97% reduction of in vitro serum thromboxane production. This aspirin regimen normalized the level of urinary thromboxane metabolites in patients with angina (17.3 +/- 3.4 ng/mmol of creatinine [10 patients], p < 0.001 from baseline level before treatment) and did not change prostacyclin metabolite levels. Atrial pacing in patients with angina not treated with aspirin caused lactate and thromboxane release into the coronary sinus. In patients with very low dose aspirin therapy, pacing did not cause thromboxane release despite inducing myocardial ischemia. However, fractional lactate extraction decreased less sharply in patients with than without aspirin therapy.

CONCLUSIONS

Thromboxane production is greatly increased in patients with stable angina. Very low dose aspirin administered to these patients reduces thromboxane synthesis to normal levels, preserves prostacyclin biosynthesis and prevents acute thromboxane release into the coronary circulation during pacing-induced ischemia. Our data suggest that platelets (not monocytes/macrophages) are activated in stable angina to produce thromboxane.

Platelet activation in stable coronary artery disease

To elucidate the role of physical activity in the pathogenesis of acute ischemic syndromes in patients with coronary artery disease (CAD), we hypothesized that platelet activation occurs when coronary blood flow velocity and shear stress increase across an atherosclerotic vascular bed. We measured platelet aggregation by using angiologic catheterization to obtain simultaneous samples of whole blood from the coronary sinus and the aorta while at rest, 2 minutes after the onset of rapid atrial pacing, and 10 minutes after termination of pacing. Of 82 consecutive patients included in our study, 36 had stenosis of the left coronary artery, 12 had stenosis of the right coronary artery only, and 34 had no evidence of CAD. Samples taken at rest revealed no arteriovenous difference in platelet aggregation between patients with CAD and those without CAD. In patients with significant stenosis (> or = 50%) of the left coronary artery, atrial pacing caused platelet aggregation to increase in samples from the coronary sinus (64 +/- 9% increase; p < 0.01) but not in blood from the aorta (2 +/- 8% decrease; difference not significant). This increase was transient, with aggregation returning almost to resting values 10 minutes after pacing ended. Atrial pacing elicited no change in platelet aggregation in samples from either the coronary sinus or aorta of patients with nonsignificant stenosis (< 50%) of the left coronary artery, patients with significant stenosis of the right coronary artery only, and patients free of CAD. Thus, under resting conditions, no evidence of platelet activation across the coronary bed was seen regardless of CAD status.(ABSTRACT TRUNCATED AT 250 WORDS)