Properties of the exchangeable splenic platelets released into the circulation during exercise-induced thrombocytosis

Causal relationship between physical activity and platelet traits: a Mendelian randomization study

Introduction: The purpose of this study was to discuss the causal relationship between physical activity and platelet traits. Methods: A dataset from a large-scale European physical activity and platelet traits was collected by using Mendelian randomization of the study. For the analysis, the inverse variance weighting method, weighted median and MR-Egger were used to estimate causal effects. The sensitivity analyses were also performed using Cochran's Q test, funnel plots and Leave-one-out analysis. Results: Light DIY, other exercises, strenuous sports, walking for pleasure were significantly associated with a decrease in platelet crit. But none of the heavy /light DIY was associated with increase in platelet crit. Other exercises and strenuous sports were associated with decrease in platelet count. Conclusion: Some types of physical activity have a causal relationship with platelet crit and platelet count. However, the types of physical activity we studied have not supported a causal relationship with mean platelet volume and platelet distribution width.

An Innovative Inducer of Platelet Production, Isochlorogenic Acid A, Is Uncovered through the Application of Deep Neural Networks

(1) Background: Radiation-induced thrombocytopenia (RIT) often occurs in cancer patients undergoing radiation therapy, which can result in morbidity and even death. However, a notable deficiency exists in the availability of specific drugs designed for the treatment of RIT. (2) Methods: In our pursuit of new drugs for RIT treatment, we employed three deep learning (DL) algorithms: convolutional neural network (CNN), deep neural network (DNN), and a hybrid neural network that combines the computational characteristics of the two. These algorithms construct computational models that can screen compounds for drug activity by utilizing the distinct physicochemical properties of the molecules. The best model underwent testing using a set of 10 drugs endorsed by the US Food and Drug Administration (FDA) specifically for the treatment of thrombocytopenia. (3) Results: The Hybrid CNN+DNN (HCD) model demonstrated the most effective predictive performance on the test dataset, achieving an accuracy of 98.3% and a precision of 97.0%. Both metrics surpassed the performance of the other models, and the model predicted that seven FDA drugs would exhibit activity. Isochlorogenic acid A, identified through screening the Chinese Pharmacopoeia Natural Product Library, was subsequently subjected to experimental verification. The results indicated a substantial enhancement in the differentiation and maturation of megakaryocytes (MKs), along with a notable increase in platelet production. (4) Conclusions: This underscores the potential therapeutic efficacy of isochlorogenic acid A in addressing RIT.

Exercise and hypoxia-induced hypercoagulability is counterbalanced in women in part by decreased platelet reactivity

Hypoxia plays an important role in several pathologies, e.g. chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, and is linked to an increased thrombosis risk. Furthermore, oxygen deprivation is associated with hypercoagulability. In this study, we investigated the effect of gender and exercise on the coagulation potential under hypoxic conditions at high altitude by assessing thrombin generation (TG) and platelet activation. Hereto, ten healthy volunteers were included (50 % male, median age of 27.5 years). The measurements were conducted first at sea level and then twice at high altitude (3883 m), first after a passive ascent by cable car and second after an active ascent by a mountain hike. As expected, both the passive and active ascent resulted in a decreased oxygen saturation and an increased heart rate at high altitude. Acute mountain sickness symptoms were observed independently of the ascent method. After the active ascent, platelet, white blood cell and granulocyte count were increased, and lymphocytes were decreased, without a gender-related difference. FVIII and von Willebrand factor were significantly increased after the active ascent for both men and women. Platelet activation was reduced and delayed under hypobaric conditions, especially in women. TG analysis showed a prothrombotic trend at high altitude, especially after the active ascent. Women had a hypercoagulable phenotype, compared to men at all 3 timepoints, indicated by a higher peak height and endogenous thrombin potential (ETP), and shorter lag time and time-to-peak. In addition, ETP and peak inhibition by thrombomodulin was lower in women after the active ascent, compared to men. Interestingly, data normalisation for subject baseline values indicated an opposing effect of altitude-induced hypoxia on α2-macroglobulin levels and TG lag time between men and women, decreasing in men and increasing in women. We conclude that hypoxia increases TG, as well as FVIII and VWF levels in combination with exercise. In contrast, platelets lose their responsiveness at high altitude, which is most pronounced after heavy exercise. Women had a more pronounced prothrombotic phenotype compared to men, which we theorize is counterbalanced under hypobaric conditions by decreased platelet activation.

Effects of exercise on platelet reactivity after myocardial infarction: a randomized clinical trial

Exercise training (ET) can lower platelet reactivity in patients with cardiovascular risk factors. However, the effects of ET on platelet reactivity in higher-risk patients is unknown. The aim of this study was to evaluate the effects of ET on platelet reactivity in patients with recent myocardial infarction (MI). Ninety patients were randomly assigned 1 month post-MI to the intervention (patients submitted to a supervised ET program) or control group. All patients were on dual antiplatelet therapy (DAPT). Platelet reactivity by VerifyNow-P2Y12 (measured by P2Y12 reaction units - PRUs) test was determined at baseline and at the end of 14 ± 2 weeks of follow-up at rest (primary endpoint), and multiplate electrode aggregometry (MEA) adenosine diphosphate (ADP) and aspirin (ASPI) tests were performed immediately before and after the maximal cardiopulmonary exercise test (CPET) at the same time points (secondary endpoints). Sixty-five patients (mean age 58.9 ± 10 years; 73.8% men; 60% ST elevation MI) completed follow-up (control group, n = 31; intervention group, n = 34). At the end of the follow-up, the mean platelet reactivity was 172.8 ± 68.9 PRUs and 166.9 ± 65.1 PRUs for the control and intervention groups, respectively (p = .72). Platelet reactivity was significantly increased after the CPET compared to rest at the beginning and at the end of the 14-week follow-up (among the intervention groups) by the MEA-ADP and MEA-ASPI tests (p < .01 for all analyses). In post-MI patients on DAPT, 14 weeks of supervised ET did not reduce platelet reactivity. Moreover, platelet reactivity was increased after high-intensity exercise (ClinicalTrials.gov: NCT02958657; https://clinicaltrials.gov/ct2/show/NCT02958657).

The effects of type of recovery in resistance exercise on responses of platelet indices and hemodynamic variables

To examine the effects of two different volume-matched resistance exercise (RE) recovery protocols (passive and active) on platelet indices and hemodynamic variables. Twelve Healthy participants (mean ± SD; 25 ± 3 yrs) completed a traditional resistance exercise (TRE) protocol that included three sets of six repetitions at 80% one repetition maximum (1RM) with two minutes passive recovery between sets, exercises and an interval resistance exercise (IRE) protocol that included three sets of six repetitions at 60%1RM followed by active recovery including six repetitions of the same exercise at 20%1RM. Blood samples for multiple platelet indices were taken before the protocols, immediately-post (IP), and after 1-hour recovery. Hemodynamic variables were measured before, IP, and every five minutes during recovery. Mean platelet volume and platelet large cell ratio P_LCR decreased from baseline to recovery. Heart rate (HR) and rate pressure product (RPP) were augmented at IP following IRE compared to TRE. HR was significantly elevated for 20 minutes after both RE protocols, and RPP recovered by five minutes. Systolic blood pressure was increased at IP compared to baseline and all recovery time points for both RE protocols. Our research demonstrated that both RE protocols, produced transient increases in platelet indices (MPV, and P_LCR) and hemodynamic variables (SBP, HR, and RPP), all of which returned to baseline within an hour. Notably, the IRE protocol elicited a greater increase in HR and RPP compared to the TRE protocol.

Impact of Physical Exercise on Platelets: Focus on Its Effects in Metabolic Chronic Diseases

Chronic disorders are strongly linked to cardiovascular (CV) diseases, and it is unanimously accepted that regular exercise training is a key tool to improving CV risk factors, including diabetes, dyslipidemia, and obesity. Increased oxidative stress due to an imbalance between reactive oxygen species production and their scavenging by endogenous antioxidant capacity is the common ground among these metabolic disorders, and each of them affects platelet function. However, the correction of hyperglycemia in diabetes and lipid profile in dyslipidemia as well as the lowering of body weight in obesity all correlate with amelioration of platelet function. Habitual physical exercise triggers important mechanisms related to the exercise benefits for health improvement and protects against CV events. Platelets play an important role in many physiological and pathophysiological processes, including the development of arterial thrombosis, and physical (in)activity has been shown to interfere with platelet function. Although data reported by studies carried out on this topic show discrepancies, the current knowledge on platelet function affected by exercise mainly depends on the type of applied exercise intensity and whether acute or habitual, strenuous or moderate, thus suggesting that physical activity and exercise intensity may interfere with platelet function differently. Thus, this review is designed to cover the aspects of the relationship between physical exercise and vascular benefits, with an emphasis on the modulation of platelet function, especially in some metabolic diseases.

The Acute and Chronic Effects of Resistance and Aerobic Exercise in Hemostatic Balance: A Brief Review

Hemostatic balance refers to the dynamic balance between blood clot formation (coagulation), blood clot dissolution (fibrinolysis), anticoagulation, and innate immunity. Although regular habitual exercise may lower the incidence of cardiovascular diseases (CVD) by improving an individual’s hemostatic profile at rest and during exertion, vigorous exercise may increase the risk of sudden cardiac death and venous thromboembolism (VTE). This literature review aims to investigate the hemostatic system’s acute and chronic adaptive responses to different types of exercise in healthy and patient populations. Compared to athletes, sedentary healthy individuals demonstrate similar post-exercise responses in platelet function and coagulatory and fibrinolytic potential. However, hemostatic adaptations of patients with chronic diseases in regular training is a promising field. Despite the increased risk of thrombotic events during an acute bout of vigorous exercise, regular exposure to high-intensity exercise might desensitize exercise-induced platelet aggregation, moderate coagulatory parameters, and up-regulate fibrinolytic potential via increasing tissue plasminogen activator (tPA) and decreasing plasminogen activator inhibitor (PAI-1) response. Future research might focus on combining different types of exercise, manipulating each training characteristic (frequency, intensity, time, and volume), or investigating the minimal exercise dosage required to maintain hemostatic balance, especially in patients with various health conditions.

Effects of two different exercise paradigms on cardiac function, BDNF-TrkB expression, and myocardial protection in the presence and absence of Western diet

Background

Brain-derived neurotrophic factor (BDNF) -tropomyosin-related kinase receptor B (TrkB) signaling is a vital regulator of myocardial performance. Here, we tested the impact of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on heart function, metabolic parameters, and serum/cardiac BDNF (with its TrkB receptor) in animals fed a Western (WD) or regular diet (ND). Further, myocardial expression of pro-inflammatory cytokine interleukin-18 (IL-18) and cardioprotective molecule heme oxygens-1 (HO-1) were monitored.

Methods

Wistar rats were divided into HIIT, MICT, and sedentary (SED), all fed a WD or ND, for 12 weeks. Heart function, protein expression, and serum factors were assessed via echocardiography, western blotting, and ELISA, respectively.

Results

WD plus SED caused insulin resistance, dyslipidemia, visceral fat deposition, serum BDNF depletion as well as cardiac upregulation of IL-18 and downregulation of HO-1, without affecting, heart function and BDNF-TrkB expression. The cardiometabolic risk factors, serum BDNF losses, and IL-18 overexpression were similarly obviated by HIIT and MICT, although HO-1 expression was boosted by HIIT exclusively (even in ND). HIIT enhanced heart function, regardless of the diet. HIIT augmented cardiac BDNF expression, with a significant difference between ND and WD. Likewise, HIIT instigated TrkB expression only in ND.

Conclusions

HIIT and MICT can cope with myocardial inflammation and cardiometabolic risk factors in WD consumers and, exclusively, HIIT may grant further protection by increasing heart function, BDNF-TrkB expression, and HO-1 expression. Thus, the HIIT paradigm should be considered as a preference for subjects who require heart function to be preserved or enhanced.

Comparison of the Levels of Hematological Parameters at Rest and after Maximum Exercise between Physically Active People with Spinal Cord Injury and Able-Bodied People

The aim of the study was to reveal the difference in the hematological reaction to the applied exercise-induced workload between the able-bodied and physically active people with cervical spinal cord injury. The study covered 11 males with spinal cord injury and 11 able-bodied persons. An incremental stress test was carried out until the maximum individual workloads were achieved. The peak oxygen uptake was measured with the use of the ergospirometric method. Venous blood test results at rest and after finishing the maximal exercise showed hemoglobin (Hb) concentration, hematocrit (HCT) value, erythrocytes (RBC), leukocytes (WBC) and platelets (PLT) counts as well as the relative percentage of granulocytes (GRA), lymphocytes (LYM), and monocytes (MON). RBC, HCT as well as Hb and PLT among people with the injury were statistically lower (p < 0.001) large effect size, than in the control group. Statistically significant difference between the test and control group, subjected to the maximal exercise stress test, was observed in the exercise induced change of the PLT [p < 0.001, (ES: 2.631)] WBC [p < 0.05, (ES: 1.429)] and the percentage of LYM and GRA [p < 0.05, (ES: 1.447) for LYM and (ES: 1.332) for GRA] between both groups, subjected to the maximal cardiac stress test on the manual cycloergometer. The analysis of the obtained results indicates that people with spinal cord injury are much more vulnerable to the occurrence of microcytic anemia compared to able-bodied people. The after-exercise percentage shift of selected subpopulations of leukocytes in both groups indicates a delayed post-exercise recovery among people with spinal cord injury.

Platelet-Rich Plasma Content of Active Spinal Cord Injured Patients: A Controlled Laboratory Study

OBJECTIVE

Platelet-rich plasma has potential uses for patients with spinal cord injuries. However, no study has quantified the cellular and growth factor content of platelet-rich plasma in this population. This study aimed to analyze (1) platelet-rich plasma content of spinal cord injury subjects and (2) the effect of high-intensity interval exercise on their platelet-rich plasma.

DESIGN

Ten spinal cord injury patients and 10 controls were enrolled. At rest, platelet-rich plasma was created from both groups. The spinal cord injury group then performed high-intensity interval exercise and underwent a second blood draw to create post-high-intensity interval exercise platelet-rich plasma. Complete blood counts and growth factor analysis (via enzyme-linked immunosorbent assay) was performed on all platelet-rich plasma.

RESULTS

The spinal cord injury group had lower platelets (305,700 ± 85,697/μl vs 380,800 ± 57,301/μl, P = 0.015) and transforming growth factor β (12.84 ± 1.58 vs 14.33 ± 0.63 ng/ml, P = 0.023). Four minutes of high-intensity interval exercise increased the platelets (305,700 ± 85,697/μl to 399,200 ± 96,251/μl, P = 0.004), leukocytes (906 ± 930 vs 2504 ± 3765/μl, P = 0.002) and transforming growth factor β (12.84 ± 1.58 to 14.28 ± 1.21 ng/ml, P = 0.020).

CONCLUSIONS

Spinal cord injury patients have fewer platelets and transforming growth factor β in their platelet-rich plasma at baseline compared with controls. Exercise increased platelet, leukocyte, and transforming growth factor β yield, compensating for the baseline deficits.

Management of venous thromboembolism in athletes

Venous thromboembolism (VTE) is a common condition with high associated morbidity and mortality. Athletes have unique VTE risk factors compared with the general population, and may have a higher than anticipated risk of thrombosis. Anticoagulant treatment poses additional challenges in athletes, as these individuals usually wish to return to sporting activities without delay. In addition, those athletes who engage in contact sports may have bleeding complications with extended anticoagulation. In this paper, we discuss VTE risk factors in athletes, the impact of exertion on haemostasis, measures which could be adopted to mitigate VTE risks in these highly active individuals and options to deal with bleeding risks from anticoagulation during injury-prone sporting activities.

High Intensity Interval Exercise Increases Platelet and Transforming Growth Factor-β Yield in Platelet-Rich Plasma

BACKGROUND

Platelet-rich plasma (PRP) is an emerging orthobiologic treatment for musculoskeletal conditions like osteoarthritis. Two studies have demonstrated the influence of longer duration exercise on PRP composition, but no study has ever explored the impact of high intensity interval exercise (HIIE) on PRP content.

OBJECTIVE

To quantify cellular and growth factor content changes in PRP after 4 minutes of HIIE.

DESIGN

Controlled laboratory pilot study.

SETTING

Academic sports medicine center.

PARTICIPANTS

Ten healthy volunteers (5 male, 5 female).

INTERVENTION

Volunteers had PRP prepared from 15 mL of whole blood using a single spin, plasma-based system (autologous conditioned plasma [ACP]) immediately before and after 4 minutes of HIIE on a stationary exercise bike (Tabata protocol).

MAIN OUTCOME MEASURE

The PRP was sent for complete blood counts and enzyme-linked immunosorbent assay (ELISA) to quantify transforming growth factor (TGF)-β, platelet-derived growth factor (PDGF), insulin-like growth factor (IGF)-1, and vascular endothelial growth factor (VEGF).

RESULTS

Mean platelet count in PRP increased from 367.4 ± 57.5 k/μL to 497.7 ± 93.3 k/μL after 4 minutes of HIIE (P < .001). TGF-β also increased from 8237.2 ± 7676.5 pg/mL to 21 535.7 ± 4062.6 pg/mL postexercise (P = .004). The other cellular components (leukocytes, red blood cells, and mean platelet volume) and growth factors (PDGF, IGF-1, and VEGF) were not significantly changed.

CONCLUSIONS

A short 4-minute bout of HIIE significantly increased the total platelet count and TGF-β concentration in PRP.

A Hypoxic Environment Attenuates Exercise-Induced Procoagulant Changes Due to Decreased Platelet Activation

Introduction  Although physical exercise is protective against cardiovascular disease, it can also provoke sudden cardiac death (exercise paradox). Epidemiological studies suggest that systemic hypoxia at high altitude is a risk factor for venous thromboembolism. Forthcoming, this study investigated the effect of repeated exercise at high altitude on blood coagulation, platelet function, and fibrinolysis. Methods  Six trained male volunteers were recruited. Participants ascended from sea level to 3,375 m altitude. They performed four exercise tests at 65 to 80% of their heart-rate reserve during 2 hours: one time at sea level and three times on consecutive days at 3,375 m altitude. Thrombin generation (TG) was measured in whole blood (WB) and platelet-rich and platelet-poor plasma. Coagulation factor levels were measured. Platelet activation was measured as αIIbβ3 activation and P-selectin expression. Fibrinolysis was studied using a clot-lysis assay. Results  Normoxic exercise increased plasma peak TG through increased factor VIII (FVIII), and increased von Willebrand factor (VWF) and active VWF levels. Platelet granule release potential was slightly decreased. After repetitive hypoxic exercise, the increase in (active) VWF tapered, and there was no more distinct exercise-related increase in peak. Platelet aggregation potential and platelet-dependent TG decreased at high altitude. There were no effects on fibrinolysis upon exercise and/or hypoxia. Conclusion  Strenuous exercise induces a procoagulant state that is mediated by the endothelium, by increasing VWF and secondarily raising FVIII levels. After repetitive exercise, the amplitude of the endothelial response to exercise diminishes. A hypoxic environment appears to further attenuate the procoagulant changes by decreasing platelet activation and platelet-dependent TG.

Myocardial infarction induces bone marrow megakaryocyte proliferation, maturation and platelet production

Platelet, apart from its classic role of homeostasis, serves also as a crucial immune cell component that contributes to the aggravation of atherosclerosis. It has been reported that myocardial infarction (MI) triggers leukocytosis in the bone marrow and spleen, which accelerates post-MI atherosclerosis. However, it remains unclear whether thrombopoiesis is also enhanced after MI. Here, using flow cytometry and bone marrow whole-mount immunofluorescence staining combined with three-dimensional (3D) reconstruction, we for the first time demonstrated an enhanced thrombopoiesis and megakaryopoiesis in a mouse model of coronary artery ligation as a mimic of MI. We showed that MI leads to increasing number of peripheral platelets, as well as elevating number and larger size of bone marrow MKs. We also observed more proplatelets and fragmented MKs, and a closer spatial distribution of MK populations to the bone marrow vascular niche after MI. This study provides direct evidence that MI induces bone marrow megakaryocyte proliferation, maturation and platelet production. It opens a new scope that targeting platelet production might become a novel therapeutic approach for attenuating post-MI atherosclerosis.

Prognostic value of rising mean platelet volume during hospitalization in patients with ST-segment elevation myocardial infarction treated with primary percutaneous coronary intervention

Background

The prognostic significance of changes in mean platelet volume (MPV) during hospitalization in ST segment elevation myocardial infarction (STEMI) patients underwent primary percutaneous coronary intervention (pPCI) has not been previously evaluated. The aim of this study was to determine the association of in-hospital changes in MPV and mortality in these patients.

Methods

Four hundred eighty consecutive STEMI patients were enrolled in this retrospective study. The patients were grouped as survivors (n = 370) or non-survivors (n = 110). MPV at admission, and at 48–72 h was evaluated. Change in MPV (MPV at 48–72 h minus MPV on admission) was defined as ΔMPV.

Results

At follow-up, long-term mortality was 23%. The non-survivors had a high ΔMPV than survivors (0.37 (− 0.1–0.89) vs 0.79 (0.30–1.40) fL, p <  0.001). A high ΔMPV was an independent predictor of all cause mortality ((HR: 1.301 [1.070–1.582], p = 0.008). Morever, for long-term mortality, the AUC of a multivariable model that included age, LVEF, Killip class, and history of stroke/TIA was 0.781 (95% CI:0.731–0.832, p <  0.001). When ΔMPV was added to a multivariable model, the AUC was 0.800 (95% CI: 0.750–0.848, z = 2.256, difference p = 0.0241, Fig. 1). Also, the addition of ΔMPV to a multivariable model was associated with a significant net reclassification improvement estimated at 24.5% (p = 0.027) and an integrated discrimination improvement of 0.014 (p = 0.0198).

Conclusions

Rising MPV during hospitalization in STEMI patients treated with pPCI was associated with long-term mortality.

Exercise and circulating BDNF: Mechanisms of release and implications for the design of exercise interventions

Engagement in regular bouts of exercise confers numerous positive effects on brain health across the lifespan. Acute bouts of exercise transiently improve cognitive function, while long-term exercise training stimulates brain plasticity, improves brain function, and helps to stave off neurological disease. The action of brain-derived neurotrophic factor (BDNF) is a candidate mechanism underlying these exercise-induced benefits and is the subject of considerable attention in the exercise-brain health literature. It is well established that acute exercise increases circulating levels of BDNF and numerous studies have sought to characterize this response for the purpose of improving brain health. Despite the interest in BDNF responses to exercise, little focus has been given to understanding the sources and mechanisms that underlie this response for the purpose of deliberately increasing circulating levels of BDNF. Here we review evidence to support that exploiting these mechanisms of BDNF release can help to optimize brain plasticity outcomes via exercise interventions, which could be especially relevant in the context of multimodal training (i.e., exercise and cognitive stimulation). Therefore, the purpose of this paper is to review the candidate sources of BDNF during exercise and the mechanisms of release. As well, we discuss strategies for maximizing BDNF responses to exercise, and propose novel research directions for advancing our understanding of these mechanisms.

Hematologic and serologic status of military working dogs given standard diet containing natural botanical supplements

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The experiments with military working dogs (MWDs) as a special case were carried out.

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Osteoarthritis is a common inflammatory disease in MWDs.

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We evaluated a mixture of natural botanicals as a dietary supplement.

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This supplementation had positive effects on hematological and serological values.

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Results provided support for the development of a feed supplement for MWDs.

The health of military working dogs (MWDs) deployed with Korean troops is of prime importance. The aim of our study was to investigate the hematologic and serologic status of Korean MWDs given natural botanical supplements. To do this, 11 natural botanicals were selected based on relevant references and combined to supplement MWDs. Throughout the 16-week experimental periods, there was no significant difference in body weights of individual dogs. The Hemoglobin (HGB), hematocrit (HCT), Mean Corpuscular Volume (MCV), and Mean Corpuscular Hemoglobin (MCH) values were slightly higher in the group given the supplement. On the other hand, the Mean Corpuscular Hemoglobin Concentration (MCHC) values were slightly lower. Changes in platelet, lymphocyte, and basophil counts were observed in the supplemented group. The median serum IL-6 level did not differ significantly between the supplemented and control groups. However, the mean serum C-reactive protein (CRP) value increased significantly from the start of supplementation to 8 weeks, and then decreased at 16 weeks. Taken together, our result suggests that the health condition of most MWDs supplemented with natural botanicals was gradually improved. Thus, this study may provide support for the development of a feed supplement for MWDs using natural botanicals.

Short-Duration Maximal and Long-Duration Submaximal Effort Forearm Exercise Achieve Elevations in Serum Brain-Derived Neurotrophic Factor

Brain-derived neurotrophic factor (BDNF) is a major orchestrator of exercise-induced brain plasticity and circulating (peripheral) BDNF may have central effects. Approximately 99% of circulating BDNF is platelet-bound, and at rest ~30% of circulating platelets are stored in the spleen. Interestingly, forearm handgrip exercise significantly elevates sympathetic outflow and has been shown to induce splenic constriction, suggesting that small muscle mass exercise could stand as a viable strategy for increasing circulating BDNF; however, the BDNF response to handgrip exercise is currently unknown. Purpose: This study examined BDNF and platelet responses to short-duration maximal (ME) and prolonged submaximal (SE) effort handgrip exercise. Methods: Healthy males (n = 18; 21.4 ± 2.1 years, BMI 25.0 ± 1.0 kg/m²) performed 10 min of ME and 30 min of SE. Blood was sampled for the determination of serum BDNF and platelet count at rest and during the last minute of exercise. Results: Compared to rest, serum BDNF significantly increased during ME (21.2%) and SE (11.2%), which displayed a non-significant trend toward an intensity-dependent response. Platelets increased in an intensity-dependent fashion compared to rest with an 8.0% increase during ME and 3.1% during SE, and these responses were significantly correlated with diastolic blood pressure responses to handgrip exercise. Further, the amount of BDNF per platelet significantly increased compared to rest during ME (13.4%) and SE (8.7%). Conclusions: Handgrip exercise evokes significant increases in serum BDNF and platelets, implicating splenic constriction as a key mechanism and confirming efficacy of this exercise model for elevating circulating BDNF.

Common Thrombotic Disorders Defined by CBC Platelet Parameters

The Coulter STKS mean platelet volume (MPV), platelet distribution width (PDW), mean corpuscular volume (MCV), and hematocrit (HCT) are assessed in thrombotic diseases. Complete blood counts (CBCs) were studied retrospectively in 645 consecutive hospital cases and, 850 "CBCs with blood films to the pathologist." Because the MPV and PDW are time dependant, nomograms and tables were created for the 0-25- and 26-40-min elapsed time intervals. In this study, abnormal CBC platelet parameters were found in the majority of patients with common thrombotic diseases, such as diabetes, atherosclerosis, hypertension, congestive heart failure, deep vein thrombosis (DVT), and toxemia. Thrombotic disease-related CBC categories include combined elevated MPV and PDW, elevated MPV or PDW alone, "MCV/MPV mismatch" (failure of physiologic "MCV/MPV match"), rheologic problem of elevated HCT and MPV, and mild thrombocytopenia with decreased MPV and high PDW. Anticoagulants and steroids often decrease the MPV. CBC platelet parameter abnormalities provide a new useful classification of thrombotic diseases in daily practice.

Splenic release of platelets contributes to increased circulating platelet size and inflammation after myocardial infarction

Acute myocardial infarction (AMI) is characterized by a rapid increase in circulating platelet size but the mechanism for this is unclear. Large platelets are hyperactive and associated with adverse clinical outcomes. We determined mean platelet volume (MPV) and platelet-monocyte conjugation (PMC) using blood samples from patients, and blood and the spleen from mice with AMI. We further measured changes in platelet size, PMC, cardiac and splenic contents of platelets and leucocyte infiltration into the mouse heart. In AMI patients, circulating MPV and PMC increased at 1-3 h post-MI and MPV returned to reference levels within 24 h after admission. In mice with MI, increases in platelet size and PMC became evident within 12 h and were sustained up to 72 h. Splenic platelets are bigger than circulating platelets in normal or infarct mice. At 24 h post-MI, splenic platelet storage was halved whereas cardiac platelets increased by 4-fold. Splenectomy attenuated all changes observed in the blood, reduced leucocyte and platelet accumulation in the infarct myocardium, limited infarct size and alleviated cardiac dilatation and dysfunction. AMI-induced elevated circulating levels of adenosine diphosphate and catecholamines in both human and the mouse, which may trigger splenic platelet release. Pharmacological inhibition of angiotensin-converting enzyme, β1-adrenergic receptor or platelet P2Y12 receptor reduced platelet abundance in the murine infarct myocardium albeit having diverse effects on platelet size and PMC. In conclusion, AMI evokes release of splenic platelets, which contributes to the increase in platelet size and PMC and facilitates myocardial accumulation of platelets and leucocytes, thereby promoting post-infarct inflammation.

Effects of Physical (In)activity on Platelet Function

As platelet activation is closely related to the liberation of growth factors and inflammatory mediators, platelets play a central role in the development of CVD. Virtually all cardiovascular risk factors favor platelet hyperreactivity and, accordingly, also physical (in)activity affects platelet function. Within this paper, we will summarize and discuss the current knowledge on the impact of acute and habitual exercise on platelet function. Although there are apparent discrepancies regarding the reported effects of acute, strenuous exercise on platelet activation, a deeper analysis of the available literature reveals that the applied exercise intensity and the subjects' cardiorespiratory fitness represent critical determinants for the observed effects. Consideration of these factors leads to the summary that (i) acute, strenuous exercise can lead to platelet activation, (ii) regular physical activity and/or physical fitness diminish or prevent platelet activation in response to acute exercise, and (iii) habitual physical activity and/or physical fitness also favorably modulate platelet function at physical rest. Notably, these effects of exercise on platelet function show obvious similarities to the well-recognized relation between exercise and the risk for cardiovascular events where vigorous exercise transiently increases the risk for myocardial infarction and a physically active lifestyle dramatically reduces cardiovascular mortality.

Effect of training status on the changes in platelet parameters induced by short-duration exhaustive exercise

It is now well known that hemostasis is directly involved in the benefits induced by physical activity. It has recently been shown that the baseline mean platelet volume (MPV) may be a predictor of endurance performance. We aimed to explore whether platelet parameters are associated with VO2max as well as running duration and speed in a short-duration exhaustive exercise test. Thirty healthy male subjects (10 sedentary and 20 trained) performed an incremental running test until exhaustion. MPV, platelet distribution width (PDW), platelet (Plt) count, and plateletcrit (Pct) were determined before exercise, immediately after exercise and after 30' recovery. Training status did not produce any difference in the baseline levels or in the post-exercise increases found in all the parameters tested. VO2max, test duration, and running speed were not correlated with any baseline parameter. Although MPV was found to be a predictor of endurance performance in long-duration exercise, the results of the present study are consistent with the hypothesis that MPV may not be a significant marker of performance in short-duration exhaustive exercise. Likewise, more research is needed to ascertain whether platelet activation is a reliable performance predictor in other exercise settings.

Effect of aerobic interval training and caffeine on blood platelet function

PURPOSE

Hyperactive platelets contribute to the thrombotic response in humans, and exercise transiently increases platelet function. Caffeine is routinely used by athletes as an ergogenic aid, but the combined effect of exercise and caffeine on platelet function has not been investigated.

METHODS

Twelve healthy males were randomly assigned to one of four groups and undertook four experimental trials of a high-intensity aerobic interval training (AIT) bout or rest with ingestion of caffeine (3 mg·kg(-1)) or placebo. AIT was 8 × 5 min at approximately 75% peak power output (approximately 80% V˙O2peak) and 1-min recovery (approximately 40% peak power output, approximately 50% V˙O2peak) intervals. Blood/urine was collected before, 60, and 90 min after capsule ingestion and analyzed for platelet aggregation/activation.

RESULTS

AIT increased platelet reactivity to adenosine diphosphate (placebo 30.3%, caffeine 13.4%, P < 0.05) and collagen (placebo 10.8%, caffeine 5.1%, P < 0.05) compared with rest. Exercise placebo increased adenosine diphosphate-induced aggregation 90 min postingestion compared with baseline (40.5%, P < 0.05), but the increase when exercise was combined with caffeine was small (6.6%). During the resting caffeine protocol, collagen-induced aggregation was reduced (-4.3%, P < 0.05). AIT increased expression of platelet activation marker PAC-1 with exercise placebo (P < 0.05) but not when combined with caffeine.

CONCLUSION

A single bout of AIT increases platelet function, but caffeine ingestion (3 mg·kg(-1)) does not exacerbate platelet function at rest or in response to AIT. Our results provide new information showing caffeine at a dose that can elicit ergogenic effects on performance has no detrimental effect on platelet function and may have the potential to attenuate increases in platelet activation and aggregation when undertaking strenuous exercise.

Effects of a TASER® conducted energy weapon on the circulating red-blood-cell population and other factors in Sus scrofa

In previous studies hematocrit has been consistently increased in an anesthetized animal model after exposures to TASER(®) conducted energy weapons (CEWs). In the present study we analyzed changes in blood cell counts and red blood cell membrane proteins following two 30-s applications of a TASER C2 device (which is designed for civilian use). Hematocrit increased significantly from 33.2 ± 2.4 (mean ± SD) to 42.8 ± 4.6 % immediately after CEW exposure of eleven pigs (Sus scrofa). Red blood cell count increased significantly from 6.10 ± 0.55 × 10(12)/L to 7.45 ± 0.94 × 10(12)/L, and mean corpuscular volume increased significantly from 54.5 ± 2.4 fl to 57.8 ± 2.6 fl. Mean corpuscular hemoglobin concentration decreased significantly from 20.5 ± 0.7 to 18.5 ± 0.6 mM. Thirty protein spots (from two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis, selected for detailed comparison) exhibited greater densities 30-min post-exposure compared with pre-exposure values. A greater number of echinocytes were observed following CEW exposure. On the basis of these results it appears that, during the strong muscle contractions produced by TASER CEWs, a specific population of red blood cells (RBCs) may be released from the spleen or other reservoirs within the body. The total time of CEW exposure in the present study was relatively long compared with exposures in common law-enforcement scenarios. Despite statistically significant changes in red blood cell counts (and other measures directly related to RBCs), the alterations were short-lived. The transient nature of the changes would be likely to counteract any potentially detrimental effects.

Breath-hold diving as a brain survival response

Elite breath-hold divers are unique athletes challenged with compression induced by hydrostatic pressure and extreme hypoxia/hypercapnia during maximal field dives. The current world records for men are 214 meters for depth (Herbert Nitsch, No-Limits Apnea discipline), 11:35 minutes for duration (Stephane Mifsud, Static Apnea discipline), and 281 meters for distance (Goran Čolak, Dynamic Apnea with Fins discipline). The major physiological adaptations that allow breath-hold divers to achieve such depths and duration are called the “diving response” that is comprised of peripheral vasoconstriction and increased blood pressure, bradycardia, decreased cardiac output, increased cerebral and myocardial blood flow, splenic contraction, and preserved O2 delivery to the brain and heart. This complex of physiological adaptations is not unique to humans, but can be found in all diving mammals. Despite these profound physiological adaptations, divers may frequently show hypoxic loss of consciousness. The breath-hold starts with an easy-going phase in which respiratory muscles are inactive, whereas during the second so-called “struggle” phase, involuntary breathing movements start. These contractions increase cerebral blood flow by facilitating left stroke volume, cardiac output, and arterial pressure. The analysis of the compensatory mechanisms involved in maximal breath-holds can improve brain survival during conditions involving profound brain hypoperfusion and deoxygenation.

The effect of agility exercise on eicosanoid excretion, oxidant status, and plasma lactate in dogs

Background

The objective was to determine the effects of agility exercise on dogs of different skill levels with respect to urinary eicosanoids, urinary 15F_2t-isoprostane (lipid peroxidation marker) and hematological/biochemical changes in plasma. Fifteen adult dogs had blood and urine samples obtained prior to, immediately and 4-hours following an agility exercise.

Results

Hematocrit, red blood cells (RBC), albumin, and hemoglobin increased following exercise, with greatest increases correlating to increased skill group (novice, intermediate, masters); at 4-hours post-exercise, hematocrit, RBC, and hemoglobin were decreased. Phosphorus increased following exercise with the greatest increase in novice and intermediates. Plasma lactate increased 3.6-fold in masters, 3.2-fold in intermediates, and 1.2-fold in novice dogs. Urine thromboxane B₂ (TXB2) more than tripled 4-hours post-exercise while 6-keto prostaglandin F_1α (PGF1α, prostacyclin metabolite), prostaglandin E₂ metabolites (13,14-dihydro-15-keto-prostaglandin A₂ and 13,14-dihydro-15-keto-prostaglandin E₂), and 13,14-dihydro-15-keto prostaglandin F_2α were unaffected as determined by a competitive enzyme immunoassay and standardized by division with urine creatinine. Urine 15F_2t-isoprostane increased insignificantly.

Conclusions

Alterations in the plasma post-exercise were likely due to hemoconcentration from insensible water loss, splenic contraction and sympathetic stimulation while 4-hours later autohemodilution reduced RBC parameters. Elevations in plasma lactate and urinary TXB2 correlated with advanced skill level/speed of the dogs.

Excess soluble CD40L contributes to blood brain barrier permeability in vivo: implications for HIV-associated neurocognitive disorders

Despite the use of anti-retroviral therapies, a majority of HIV-infected individuals still develop HIV-Associated Neurocognitive Disorders (HAND), indicating that host inflammatory mediators, in addition to viral proteins, may be contributing to these disorders. Consistently, we have previously shown that levels of the inflammatory mediator soluble CD40L (sCD40L) are elevated in the circulation of HIV-infected, cognitively impaired individuals as compared to their infected, non-impaired counterparts. Recent studies from our group suggest a role for the CD40/CD40L dyad in blood brain barrier (BBB) permeability and interestingly, sCD40L is thought to regulate BBB permeability in other inflammatory disorders of the CNS. Using complementary multiphoton microscopy and quantitative analyses in wild-type and CD40L deficient mice, we now reveal that the HIV transactivator of transcription (Tat) can induce BBB permeability in a CD40L-dependent manner. This permeability of the BBB was found to be the result of aberrant platelet activation induced by Tat, since depletion of platelets prior to treatment reversed Tat-induced BBB permeability. Furthermore, Tat treatment led to an increase in granulocyte antigen 1 (Gr1) positive monocytes, indicating an expansion of the inflammatory subset of cells in these mice, which were found to adhere more readily to the brain microvasculature in Tat treated animals. Exploring the mechanisms by which the BBB becomes compromised during HIV infection has the potential to reveal novel therapeutic targets, thereby aiding in the development of adjunct therapies for the management of HAND, which are currently lacking.

The effects of low-dose epinephrine infusion on spleen size, central and hepatic circulation and circulating platelets

In several conditions associated with adrenergic stimulation, an increase in peripheral count of larger platelets has been observed, but the mechanism remained elusive. Larger platelets have greater prothrombotic potential and increase the risk of acute thrombotic events. The human spleen retains one-third of total body platelets, with mean volume (MPV) about 20% greater than that of circulating platelets. We aimed to answer whether low-dose epinephrine infusion results in spleen contraction and MPV increase. We undertook the continuous ultrasonic measurements of spleen volume, hepatic and central circulation with concurrent blood sampling in response to intravenous infusion of epinephrine (6 min of 0·06 µg kg(-1) per min, followed by 3 min of 0·12 µg kg(-1) per min) in nine healthy young subjects. The spleen volume started to decrease immediately after the onset of infusion, in the presence of substantial decreases in peripheral resistance and mean blood pressure and increases in heart rate and cardiac output. The majority of spleen emptying, approximately 25%, (95% CI 71·3-299·7) was observed 1 min after infusion onset, the hepatic vein flow peaked at the end of infusion for 28·4% (95% CI 1074·6-407·9), while increases in platelet count for approximately 31% (95% CI 187·8-314·8) and MPV for 4·4% (95% CI 7·3-10·9) lagged until 1 min after infusion cessation. We suggest that spleen is a dynamic reservoir of large platelets, which are mobilized even by low-dose epinephrine infusion in conditions of decreased blood pressure.

Effects of resistance exercise and protein ingestion on blood leukocytes and platelets in young and older men

This study investigated, in a multi-experiment design, the acute effects of milk protein ingestion, aging [50 young (approximately 26 years) vs. 45 older (approximately 61 years) men] and training state for the blood leukocyte and platelet responses acutely after a single bout of resistance exercise (RE). Moreover, basal effects of 21 weeks of resistance training (RT) were examined. The single bout of RE rapidly increased all blood leukocytes and platelets (P < 0.05). Protein ingestion before or before and after the RE bout did not have an effect on this response. However, younger men had a larger immediate exercise-induced response in leukocytes and platelets than older men. Basal fasting levels of leukocytes and platelets remained unchanged after 21 weeks of RT and this RT period did not change the acute RE-induced leukocyte and platelet response. The long-term RT was, however, able to slightly increase blood hematocrit. Blood platelet counts were consistently higher in the younger men when compared to the older men. Blood lymphopenia occurred only after a larger volume of exercise. In conclusion, the acute increase in blood leukocytes and platelets may be smaller in the older as when compared to the younger men. However, the number of immune cells and thus probably their function may not be affected by milk protein ingestion or months of resistance training.

Effects of enoxaparin and unfractionated heparin on platelet activity and reactivity during carotid endarterectomy

The aim of this study was to determine platelet activity and reactivity and the effects of unfractionated heparin (UFH) and enoxaparin on platelet function during carotid eversion endarterectomy under local anesthesia. Twenty symptomatic patients undergoing carotid endarterectomy were randomly assigned to either 5,000 units of UFH or body weight-adjusted enoxaparin (0.5 mg/kg body weight) as an intraoperative intravenous bolus. The activity of platelets was assessed by measuring the expression of CD62p and CD41 with flow cytometry. Additionally, platelet-leukocyte aggregates (PLAs) were enumerated. The reactivity of platelets was evaluated by measuring the expression of the same antigens after stimulation. In addition, platelet reactivity was also analyzed using a PFA-100 analyzer. A significant increase in platelet activity was observed during surgery for CD41 and CD62p (p = .002 and < .001, respectively). The number of PLAs showed no significant changes during surgery. Yet there was a significant difference between patients treated with UFH and patients treated with enoxaparin. No difference for platelet activity or reactivity for patients receiving either UFH or enoxaparin prior to cross-clamping of the carotid arteries was seen. The formation of PLAs after endarterectomy was significantly higher in the UFH group; thus, PLAs are probably a useful surrogate parameter for measuring platelet activity.

Primary and secondary thrombocytosis in childhood

This review summarizes current data on the pathomechanisms and clinical aspects of primary and secondary thrombocytosis in childhood. Primary thrombocytosis is extremely rare in childhood, mostly diagnosed at the beginning of the second decade of life. As in adults, the criteria of the Polycythemia Vera Group are appropriate to diagnose primary thrombocytosis. The pathomechansims of non-familial forms are complex and include spontaneous formation of megakaryopoietic progenitors and increased sensitivity to thrombopoietin (Tpo). Familial forms can be caused by mutations in Tpo or Tpo receptor (c-mpl) genes. These mutations result in overexpression of Tpo, sustained intracellular signalling or disturbed regulation of circulating Tpo. Treatment of primary thrombocytosis is not recommended if platelet counts are <1500/nl and bleeding or thrombosis did not occur in patient's history. In severe cases, decision on treatment should weigh potential risks of treatment options (hydroxyurea, anagrelide) against expected benefits for preventing thrombosis or haemorrhage. Secondary thrombocytosis is frequent in children, in particular in the first decade of life. Hepatic Tpo production is stimulated in acute response reaction to a variety of disorders. Thrombosis prophylaxis is not required, even at platelet counts >1000/nl, except for cases with additional prothrombotic risk factors.

The effects of graded resistance exercise on platelet aggregation and activation

PURPOSE

The purpose of this study was to examine the effects of resistance exercise with varying intensity but with similar volume on platelet aggregation and activation.

METHODS

Thirteen healthy male subjects randomly completed three resistance exercise test trials at an intensity corresponding to 40%, 60%, and 80% of one repetition maximum (1-RM) in which the subjects performed six exercises including upper- and lower-body parts. Venous blood samples were obtained before and immediately after each exercise trial and analyzed for platelet count (PLT), plateletcrit (PCT), mean platelet volume (MPV), platelet aggregation, and beta-thromboglobulin (B-TG). Plasma volume changes were estimated from hemoglobin and hematocrit readings before and after each exercise trial.

RESULTS

Although all exercise trials were followed by a significant (P < 0.05) increase in PLT (thrombocytosis), PCT, and MPV, this rise was not related to the exercise intensity (P > 0.05). Exercise was also followed by a significant increase (P < 0.05) in platelet aggregation, but this only occurred with the high but not with the low concentrations of adenosine diphosphate (ADP). Although ANOVA showed a significant overall increase (P < 0.05) in the concentration of B-TG after exercise, this rise only reached the assigned level of significance (P < 0.05) after 80% exercise trial.

CONCLUSION

It was concluded therefore that resistance exercise is followed by an increase in PLT, PCT, and MPV, and this occurred in parallel with an in vivo activation of platelet as manifested by an increase in platelet aggregation and a rise in B-TG.

Uneven changes in circulating blood cell counts with adrenergic stimulation to the canine spleen

1. Responses of splenic diameter measured by sonomicrometry to alpha- and beta-adrenoceptor stimulants were estimated together with simultaneously measured systemic arterial and splenic venous concentrations of red blood cells (RBC), white blood cells (WBC) and platelets (PLT) in anaesthetized dogs. 2. Intravenous and intrasplenic arterial injections of adrenaline, noradrenaline and phenylephrine all produced profound decreases in splenic diameter. Increases in systemic arterial concentrations of RBC produced by these stimulants were observed immediately following the splenic contraction and marked increases in splenic venous concentration of RBC. 3. Adrenaline and noradrenaline both caused rapid and transient decreases in WBC release from the spleen and these agonists then, in addition to phenylephrine, caused gradual and small increases in systemic arterial WBC concentrations. The increases in arterial RBC and WBC concentrations were abolished by transient isolation of the spleen from the systemic circulation. These three agents did not significantly modify differences between splenic venous and systemic arterial concentrations of PLT. 4. Intra-arterial injections of isoprenaline caused an increase in splenic diameter and a significant decrease in the splenic venous concentration of WBC, but barely influenced the veno-arterial differences in RBC and PLT concentrations across the spleen. 5. The present results indicate that contraction of the spleen through stimulation of splenic alpha1-adrenoceptors contributes to supplying RBC but not PLT into the systemic circulation, whereas splenic beta-adrenoceptor activation leads to splenic dilatation with increased sequestration of WBC to the spleen despite no changes in the release of RBC and PLT from the spleen.

Platelet serotonin transporter density and related parameters in endurance-trained and sedentary male subjects

A number of peripheral indices of serotonergic function were examined in endurance-trained (ET) and sedentary males using the blood platelet as a model of the serotonergic neurone. The aim of the study was to investigate possible involvement and adaptation of the central serotonergic system in exercise-induced fatigue. The [3H] paroxetine-defined density of platelet serotonin transporters, platelet serotonin content and the plasma concentration of amino acids were determined in 10 ET and eight sedentary males. The mean (standard deviation) density of the serotonin transporter in the platelet membranes of the ET subjects was greater [1237 (182) fmol mg protein-1] than that of the sedentary subjects [910 (119) fmol mg protein-1; P = 0.013]. No difference (P = 0.51) could be seen between the median (range) platelet serotonin content of the ET subjects [0.98 (0.37-3.04) nmol platelet-10] and that of the sedentary subjects [0.82 (0.18-1.49) nmol platelet-10]. The platelet poor plasma concentrations of tryptophan and tyrosine were lower in the ET subjects (P = 0.028 and 0.015, respectively). The present study suggests that the platelet membrane of the ET subjects has a greater density of the serotonin transporter and that this is inversely related to the circulating concentration of the serotonin precursor, tryptophan. It remains to be resolved whether the increase in serotonin transporter density in the platelet membrane of ET subjects is reflected centrally and whether the ET platelet population may be sufficiently different from that of sedentary individuals to alter serotonin transporter density.

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.

Effects of treatment with oral isosorbide dinitrate on platelet function in vivo; a double-blind placebo-controlled study in patients with stable angina pectoris

1. A randomised double-blind placebo-controlled cross-over study was performed to investigate the effects of oral isosorbide dinitrate (ISDN; 20 mg twice daily for 2 weeks) on various aspects of platelet function in vivo in 20 patients with stable angina pectoris. Measurements were performed at rest and after platelet activation by physical exercise (bicycle ergometry). 2. Compared with placebo, treatment with ISDN significantly decreased systolic blood pressure at rest by 7 (-14 to -1) mm Hg (mean and 95% CI) and tended to increase exercise capacity by 7 (-1 to 14) W and attenuate perceived chest pain during maximal work. The dosage was high, as judged by side-effects reported (mainly headache). Compliance was good, as assessed by electronic counter equipped tablet bottles (Medication Event Monitoring System); only one patient had a compliance rate below 60%. 3. Exercise significantly increased platelet aggregability as measured by filtragometry ex vivo; the time taken for platelet aggregates in whole blood drawn directly from an antecubital vein to occlude a microfilter was significantly decreased from 155 to 95 s (antilog of mean log values). Platelet secretion in vivo also increased, as indicated by significant elevations of beta-thromboglobulin in plasma; from 22 to 35 ng ml-1 (P = 0.006). 4. ISDN treatment did not inhibit platelet function. Relative to placebo, filtragometry readings (ISDN/placebo ratios; mean and 95% CI) were not altered either at rest (1.05 (0.83 to 1.32)) or immediately after exercise (0.98 (0.80 to 1.20)). Similarly, beta TG in plasma was unaltered by ISDN treatment; 1.09 (0.98 to 1.21) at rest, and 1.04 (0.82 to 1.30) immediately after exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Platelet volume: laboratory measurement and clinical application

Modern cell analyzers routinely produce platelet indices, but many clinicians do not utilize them in clinical decision-making. In part this can be attributed to difficulties with their laboratory measurement. The mean platelet volume is dependent on a number of variables, including time of analysis after venepuncture, method of analysis, anticoagulant used and specimen storage temperature. The influence of these laboratory variables is significant and reproducible mean platelet volumes are dependent on standardized laboratory methodology. When pre-analysis factors are controlled, alterations in platelet volume can be demonstrated in a number of disease states and assessment of platelet volume can be useful in the monitoring and diagnosis of patients. An understanding of the pathophysiology of alterations in platelet volume and of the inverse relationship between platelet volume and count is a prerequisite for the successful clinical application of platelet volume measurements.