Exercise-induced changes in platelet aggregation; a comparison of whole blood and platelet rich plasma techniques

Screening and diagnosis of inherited platelet disorders

Inherited platelet disorders are important conditions that often manifest with bleeding. These disorders have heterogeneous underlying pathologies. Some are syndromic disorders with non-blood phenotypic features, and others are associated with an increased predisposition to developing myelodysplasia and leukemia. Platelet disorders can present with thrombocytopenia, defects in platelet function, or both. As the underlying pathogenesis of inherited thrombocytopenias and platelet function disorders are quite diverse, their evaluation requires a thorough clinical assessment and specialized diagnostic tests, that often challenge diagnostic laboratories. At present, many of the commonly encountered, non-syndromic platelet disorders do not have a defined molecular cause. Nonetheless, significant progress has been made over the past few decades to improve the diagnostic evaluation of inherited platelet disorders, from the assessment of the bleeding history to improved standardization of light transmission aggregometry, which remains a "gold standard" test of platelet function. Some platelet disorder test findings are highly predictive of a bleeding disorder and some show association to symptoms of prolonged bleeding, surgical bleeding, and wound healing problems. Multiple assays can be required to diagnose common and rare platelet disorders, each requiring control of preanalytical, analytical, and post-analytical variables. The laboratory investigations of platelet disorders include evaluations of platelet counts, size, and morphology by light microscopy; assessments for aggregation defects; tests for dense granule deficiency; analyses of granule constituents and their release; platelet protein analysis by immunofluorescent staining or flow cytometry; tests of platelet procoagulant function; evaluations of platelet ultrastructure; high-throughput sequencing and other molecular diagnostic tests. The focus of this article is to review current methods for the diagnostic assessment of platelet function, with a focus on contemporary, best diagnostic laboratory practices, and relationships between clinical and laboratory findings.

Pseudospontaneous Platelet Aggregation and Spuriously Elevated Blood Cell Counts in Cryoglobulinemia

Cryoglobulinemia has been reported sometimes to cause false elevation in platelet and/or leukocyte counts in au tomated blood cell counters due to temperature-dependent pro tein precipitates that are falsely interpreted as blood cells at room temperature. Upon heating to 37°C, these blood counts decrease to normal levels as cryoproteins dissolve. Therefore, cryoglobulins could theoretically lead to erroneous diagnosis of spontaneous platelet aggregation in platelet counting and tur bidometric methods as platelet count and turbidity of the plate let-rich plasma decrease at 37°C, respectively. Here, the event of pseudospontaneous platelet aggregation is confirmed in two patients with mixed cryoglobulinemia, both had spuriously el evated blood cell counts.

Effect of strenuous arm crank exercise on platelet function in patients with spinal cord injury

OBJECTIVE

To investigate the effects of arm crank exercise on various platelet functions and prostacyclin in individuals with spinal cord injury (SCI).

DESIGN

Case-control study.

SETTING

Research project at a hospital-based exercise physiology laboratory.

PARTICIPANTS

Seven men (with lesions at levels T11, n = 1; T12, n = 2; L1, n = 2; L2, n = 2) and 3 women (T12, n = 1; L1, n = 2) in the SCI group had SCI for at least 6 weeks. Ten age- and gender-matched healthy people who had not engaged in any regular physical activity for at least 1 year were selected as the control group.

INTERVENTION

All subjects exercised strenuously by using an arm crank engometer.

MAIN OUTCOME MEASURE

Platelet adhesiveness on fibrinogen-coated surface and epinephrine-induced aggregation in vitro, plasma soluble P-selectin (sP-selectin), and urinary 6-keto-prostaglandin F(1alpha) (6-keto PGF(1alpha)) levels.

RESULTS

The SCI group had higher platelet adhesiveness and aggregability and plasma sP-selectin level, but lower urinary 6-keto PGF(1alpha) level than the control group. Platelet adhesiveness and aggregability were enhanced by strenuous arm exercise in all subjects, but only in the SCI group was sP-selectin level increased by exercise. Strenuous exercise raised the levels of 6-keto PGF(1alpha) in control group subjects, but not in subjects with SCI.

CONCLUSIONS

Individuals with SCI had more extensive basal and exercise-induced platelet activation and sP-selectin release than people without SCI. Moreover, strenuous arm exercise, which enhanced the release of prostacyclin in healthy subjects, failed to do so in those with SCI.

Inhibition by combined therapy with ticlopidine and aspirin of enhanced platelet aggregation during physical exercise in patients with coronary artery disease

BACKGROUND

Strenuous exercise can be a major trigger for coronary thrombosis and it enhances platelet aggregation.

METHODS

We evaluated the effect of antiplatelet therapy on shear stress-induced platelet aggregation (SIPA), in addition to agonist-induced aggregation, before and immediately after ergometer exercise in patients with stable coronary artery diseases (CAD). Forty-eight patients with stable CAD were randomly distributed into 3 groups: no antiplatelet drug (patient control, n = 16), aspirin (ASA) monotherapy (n = 16), and combined therapy with ticlopidine (TIC) and ASA (n = 16).

RESULTS

There were significant increases in not only adenosine phosphate (ADP)- and collagen-induced platelet aggregation but also in SIPA during exercise by the patient control group. ASA monotherapy did not attenuate the enhanced ADP-induced aggregation nor SIPA. Combined ASA + TIC therapy significantly inhibited SIPA as well as ADP-induced aggregation both before and after exercise. Significant increases in levels of plasma von Willebrand factor (vWF) occurred during exercise, and these antiplatelet therapies had no apparent effect on increased vWF levels during exercise. Exercise induced a significant increase in the plasma thrombin-antithrombin III complex level with no significant changes in the level of plasmin-plasmin inhibitor complex level in all 3 groups.

CONCLUSIONS

Combined therapy with ASA + TIC effectively inhibited increased platelet aggregability in response to acute exercise, with no effects on coagulant or fibrinolytic potentials in patients with CAD. The data suggest that TIC combined with ASA may be superior to ASA alone in preventing acute coronary events during exercise in patients with coronary atherosclerotic disease.

Upright posture and maximal exercise increase platelet aggregability and prostacyclin production in healthy male subjects

BACKGROUND

It is well accepted that heavy physical exertion can trigger the onset of myocardial infarction, but the mechanism is uncertain. As platelet and endothelial function play an important role in thrombotic events, platelet and prostacyclin responses to maximal treadmill exercise were studied.

METHODS/RESULTS

The study subjects were 40 healthy men, mean (SEM) age 29 (5) years. Platelet aggregation was measured on a four channel aggregometer. Plasma 6-keto-prostaglandin F1alpha was analysed using an enzyme immunoassay technique. Upright posture and exercise produced an increase in platelet aggregability, as indicated by a fall in the threshold concentration of adrenaline (epinephrine) from 7.6 (1.5) microM at rest to 4.3 (1.0) microM after exercise (p = 0.002). The collagen lag time became significantly shorter with exercise (from 79.1 (3.1) seconds at rest to 71.9 (2.6) seconds after exercise, p = 0.003). Exercise was also associated with a 55% increase in plasma 6-keto-prostaglandin F1alpha (from 38.1 (75%CI 29.0 to 46.5) pg/ml at rest to 59.2 (47.3 to 66.8) pg/ml after exercise, p<0.001).

CONCLUSIONS

In healthy male subjects, upright posture and maximal exercise increased platelet aggregability but this increase was counteracted by an increase in prostacyclin production. In patients with endothelial dysfunction, a reduced prostacyclin response to exercise may promote a transient prothrombotic imbalance that may trigger cardiovascular disease onset.

Effects of short-term exercise on female platelet function during different phases of the menstrual cycle

Previous studies have shown that premenopausal women have a low incidence of cardiovascular diseases, and that acute exercise affects male platelet function in an intensity-dependent manner. To investigate whether acute exercise affects female platelet function differently from males, sixteen sedentary women in the midfollicular phase or midluteal phase received strenuous or moderate exercise on a bicycle ergometer. Before and immediately after exercise, platelet adhesiveness, adenosine diphosphate-induced platelet aggregation and intracellular calcium concentration elevation, platelet cAMP and cGMP contents, urinary 11-dehydro-TXB2 and 6-keto-prostaglandin F1 alpha levels, and plasma nitric oxide metabolite level were determined. Our results showed no differences in exercise performance and in resting platelet function between two menstrual phases, with little change in urinary eicosanoid metabolites and platelet cAMP levels under all experimental conditions. In addition, for women in the midfollicular phase, (1) strenuous exercise increased platelet adhesiveness, adenosine-diphosphate-induced platelet aggregation, and intracellular calcium concentration elevation, whereas moderate exercise suppressed them; (2) moderate exercise enhanced plasma nitric oxide metabolite and platelet cGMP levels. In contrast, none of these platelet functions was affected by acute exercise in the midluteal phase. Therefore, we conclude that acute exercise affects female platelet function in an intensity-dependent manner in the midfollicular phase but not in the midluteal phase. The irresponsiveness of platelets to acute exercise in the luteal phase may partially explain why premenopausal women have a lower incidence of cardiovascular diseases than men.

Mechanisms underlying the morning increase in platelet aggregation: a flow cytometry study

OBJECTIVES

Mechanisms underlying the morning increase in platelet aggregation produced by arising and assuming the upright posture were studied by examining 1) the expression on the platelet surface of activation-dependent markers; 2) platelet aggregation in whole blood; and 3) hematologic factors likely to influence aggregation.

BACKGROUND

The morning increase in thrombotic cardiovascular events has been attributed, in part, to the morning surge in platelet aggregability, but its mechanisms are poorly understood.

METHODS

Expression of seven platelet surface antigens (including P-selectin, activated GPIIb,IIIa and GPIb-IX), whole-blood platelet aggregation, platelet count and hematocrit were measured before and after arising in 17 normal volunteers. The fibrinolytic variables, tissue-type plasminogen activator, plasminogen activator inhibitor 1 and catecholamine levels were also measured.

RESULTS

On arising and standing, platelet aggregation increased by 71% (p < 0.01) and 27% (p < 0.03) in response to collagen and adenosine diphosphate, respectively. However, there was no change in any of the activation-dependent platelet surface markers. Whole-blood platelet count and hematocrit increased by 15% and 7% (both p < 0.0001), respectively. Norepinephrine and epinephrine levels increased by 189% (p < 0.0001) and 130% (p < 0.01), respectively. Tissue-type plasminogen activator antigen increased (31%, p < 0.01), but there was no significant increase in plasminogen activator inhibitor 1, suggesting an overall increase in fibrinolysis on standing. Prothrombin fragment 1.2 increased by 28% (p < 0.02), indicating a small increase in thrombin generation. The increases in hematocrit and platelet count that occurred on standing were carefully mimicked in vitro and resulted in a 115% (p < 0.05) increase in platelet aggregation in response to adenosine diphosphate.

CONCLUSIONS

These data demonstrate that the morning increase in platelet aggregation is not accompanied by expression of activation-dependent platelet surface receptors and suggest that the increase in whole-blood aggregation may be primarily due to the increases in catecholamine levels, platelet count and hemoconcentration.

Different effects of strenuous exercise and moderate exercise on platelet function in men

BACKGROUND

Platelets play an important role in the pathogenesis of cardiovascular diseases. It is also noticed that on one hand, regular exercise can reduce the risk of cardiovascular diseases, and on the other hand, vigorous exercise provokes sudden cardiac death. We therefore hypothesize that various intensities of exercise may affect platelet function differently.

METHODS AND RESULTS

Strenuous and moderate exercise (about 50% to 55% of peak oxygen consumption, VO2peak) on a bicycle ergometer in 10 sedentary and 10 physically active healthy young men was executed on two separate occasions. Blood samples were collected before and immediately after exercise. A newly designed tapered parallel plate chamber was used to assess platelet adhesiveness. Platelet aggregation induced by ADP was evaluated by the percentage of reduction in single platelet count. beta-Thromboglobulin (beta-TG) and platelet factor 4 (PF4) were measured by ELISA. In addition, a similar study on 5 patients with stable angina were also conducted. Our results showed that (1) in the sedentary healthy group, platelet adhesiveness and aggregation were increased by strenuous exercise and depressed by moderate exercise; (2) in the active healthy group, platelet adhesiveness and aggregation were enhanced by severe exercise, whereas only aggregation was decreased by moderate exercise; (3) in the patients with stable angina, platelet adhesiveness and aggregation were enhanced by strenuous exercise and adhesiveness was suppressed by moderate exercise; (4) the degree of hemoconcentration induced by acute exercise tended to be related to the severity of exercise in all subjects; and (5) although severe exercise elevated beta-TG and PF4, there were no significant changes in beta-TG, PF4, and the ratio of beta-TG to PF4 in healthy subjects after exercise.

CONCLUSIONS

It is concluded that platelet adhesiveness and aggregability may be sensitized by strenuous exercise in both healthy subjects and patients with stable angina. In contrast, platelet function can be suppressed significantly by moderate exercise in the healthy and tends to be depressed in patients with stable angina. The former may increase the risk of cardiac arrest and the latter may protect us from cardiovascular diseases. In addition, the effects of acute exercise tend to be more pronounced in the sedentary than in the active.

Effect of strenuous exercise on platelet activation state and reactivity

BACKGROUND

It has been hypothesized that platelets are activated, or made more activatible, by strenuous exercise and that these changes may play a role in the genesis of exercise-induced coronary ischemia. Previous studies have yielded conflicting results but have used assays (eg, platelet aggregation, plasma platelet factor 4, and plasma beta-thromboglobulin) that are subject to methodological problems.

METHODS AND RESULTS

In the present study, a whole blood flow cytometric method was used to study the platelet activation state and reactivity of 12 physically active and 12 sedentary individuals before and after standardized treadmill exercise testing. The peptide gly-pro-arg-pro (GPRP) was included in this assay to prevent fibrin polymerization and platelet aggregation, thus allowing the measurement of the reactivity to thrombin of individual platelets in the physiological milieu of whole blood. A panel of fluorescent-labeled monoclonal antibodies was used to monitor activation-dependent platelet surface changes: downregulation of glycoprotein (GP) Ib (6D1) and upregulation of GMP-140 (S12), the GPIIb-IIIa complex (PAC1), and GPIV (OKM5). In samples obtained before exercise, platelets not exposed to thrombin showed no evidence of in vitro activation. In the sedentary subjects, exercise caused a consistent and significant augmentation of the platelet activation state and reactivity as judged by the binding of 6D1 in the presence of thrombin 0.05 U/mL (P < .001), 0.005 U/mL (P = .001), and 0 U/mL (P = .004) and by the binding of OKM5 in the presence of thrombin 0.05 U/mL (P < .001), 0.005 U/mL (P = .029), and 0 U/mL (P = .035). Exercise increased the binding of PAC1 at only a single thrombin concentration (0.005 U/mL, P = .027) and did not alter the binding of S12 at any thrombin concentration. In contrast, in the physically active subjects, exercise failed to cause a consistent alteration in either platelet activation state or platelet reactivity. No significant differences were found between the 12 male and 12 female volunteers.

CONCLUSIONS

Strenuous exercise in sedentary subjects but not physically active subjects resulted in both platelet activation and platelet hyperreactivity. These changes were more readily detected with monoclonal antibodies directed against GPIb (6D1) and, to a lesser extent, GPIV (OKM5) rather than those directed against the GPIIb-IIIa complex (PAC1) and GMP-140 (S12). Platelet activation by thrombin, generally regarded as the most physiologically important agonist, can be studied in whole blood in a clinical setting through the use of the peptide GPRP.

Effects of an oral dose of isosorbide dinitrate on platelet function and fibrinolysis in healthy volunteers

1. A randomised double-blind placebo-controlled study was performed to investigate the effects of isosorbide dinitrate (ISDN; 20 mg orally) on various aspects of platelet function and fibrinolysis in vivo in 12 healthy volunteers. 2. Measurements were performed at rest (before and after tablet ingestion) and during platelet activation by adrenaline (0.4 nmol kg-1 min-1; 30 min infusion). 3. At rest, ISDN did not alter plasma concentrations of beta-thromboglobulin (beta TG). EC50 values for ADP induced aggregation in vitro (Born aggregometry) or ex vivo filtragometry readings. Adrenaline markedly increased platelet aggregability in vivo as measured by filtragometry and elevated levels of beta TG in plasma. ISDN treatment did not affect these responses in the group as a whole. 4. Individuals responding to ISDN with more pronounced vasodilatation at rest showed a lesser increase in aggregability during the ensuing adrenaline infusion (r = -0.66, P = 0.02) despite higher adrenaline levels during ISDN. In individuals showing a significant decrease in systolic blood pressure (n = 8) ISDN tended to attenuate the adrenaline induced increase in platelet aggregability (filtragometry; P = 0.08), despite higher plasma adrenaline and noradrenaline levels after ISDN ingestion. 5. Plasma concentrations of ISDN and its active metabolites isosorbide-5-mononitrate and isosorbide-2-mononitrate were not correlated to haemodynamic or platelet variables. 6. Fibrinolytic activity (t-PA antigen and activity, PAI-1 antigen and activity) increased similarly during the adrenaline infusion following ISDN and placebo. 7. It is concluded that ISDN may affect platelet aggregation responses to adrenaline in vivo, but only in individuals showing significant haemodynamic responses to ISDN.(ABSTRACT TRUNCATED AT 250 WORDS)

'Spontaneous' platelet aggregation in whole blood in diabetic patients with and without microvascular disease

Consistent abnormalities of agonist-induced platelet aggregation, in either whole blood or platelet rich plasma, have not been demonstrated in diabetic patients without microvascular disease. In the present study platelet aggregation in the absence of exogenous agonists ('spontaneous' aggregation) was compared between 22 non-diabetic subjects and 23 Type 1 diabetic patients with (n = 12) and without (n = 11) microvascular disease. 'Spontaneous' aggregation was determined by measuring the percentage fall in single platelet number in aliquots of whole blood shaken for 60 min. Diabetic patients without microvascular disease had fewer single platelets remaining (greater aggregation) than non-diabetic subjects at all time-points (69.7 +/- 6.6 vs 82.3 +/- 7.3% at 60 min p less than 0.001), but more platelets remaining than in diabetic patients with microvascular disease at all time-points (69.7 +/- 6.6 vs 61.0 +/- 7.8% at 60 min p less than 0.02). No significant correlations were observed between platelet aggregation and plasma glucose, blood cell counts, or glycated haemoglobin levels. The study suggests that platelet abnormalities antedate the appearance of microvascular disease in diabetic patients.

Platelet aggregability in humans: contrasting in vivo and in vitro findings during sympatho-adrenal activation and relationship to serum lipids

Platelet aggregability was studied in 18 healthy volunteers during mental stress (a colour word test; CWT) and low- and high-dose adrenaline infusions using an ex vivo technique (filtragometry) and conventional in vitro aggregometry. CWT and high-dose adrenaline (3.4 nmol l-1 in plasma) shortened filtragometry readings, suggesting increased platelet aggregability in vivo. Low-dose adrenaline had no effect despite higher adrenaline levels in plasma (0.9 nmol l-1) than during CWT (0.4 nmol l-1). Platelet sensitivity to ADP in vitro was reduced following CWT and further reduced following adrenaline infusions. In vitro, adrenaline (50 nmol l-1) had little effect on platelet aggregation per se, but enhanced aggregability evoked by ADP (at ED50). Adrenaline potentiation of ADP-induced aggregation was enhanced after CWT, but was not related to filtragometry responsiveness to stress in vivo. Serum LDL-cholesterol levels were inversely correlated to filtragometry readings at rest, suggesting an adverse influence on platelet aggregability in vivo. HDL-cholesterol levels were inversely correlated to platelet sensitivity to ADP in vitro, suggesting a positive influence. Thus, sympatho-adrenal activation enhances platelet aggregability in vivo (as assessed by ex vivo filtragometry), but adrenaline alone cannot explain the pro-aggregatory effect of mental stress. Serum lipoprotein alterations associated with increased risk for atherosclerosis seem to enhance platelet aggregability. The conventional in vitro technique may poorly reflect platelet aggregability in vivo.

The effects of dopexamine, a new dopamine analogue, on platelet function in stress

1. Dopexamine is a novel analogue of dopamine which is free of alpha-adrenoceptor activity and is of therapeutic value in chronic heart failure. The effects of dopexamine on the in vitro function of platelets from 10 healthy subjects at rest, after exercise and after in vitro addition of adrenaline and noradrenaline were investigated. 2. Dopexamine in a wide range of concentrations (10(-9)M-10(-3)M) did not appear to function as an agonist on platelets either in whole blood or in PRP preparations. 3. Dopexamine caused a dose-dependent inhibition of agonist-induced platelet aggregation in both whole blood and PRP. The inhibitory effect of dopexamine was significantly greater in PRP than in whole blood, and significantly greater to adrenaline than to collagen or ADP as agonists in whole blood. 4. After exercise or after in vitro addition of adrenaline and noradrenaline at concentrations commonly seen in myocardial infarction, dopexamine produced similar levels of inhibition seen with platelets from resting subjects. 5. Dopexamine did not affect plasma catecholamine levels but caused an increase in intraplatelet noradrenaline levels. 6. This study suggests that dopexamine is unlikely adversely to affect the hyperaggregable state found in patients with cardiogenic shock after myocardial infarction.