In-vivo Platelet Activation and Anomalous Thrombospondin Levels in Severe Falciparum Malaria

To investigate in vivo platelet function in acute falciparum malaria plasma concentrations of β-thromboglobulin (β-TG), platelet factor 4 (PF4) and thrombospondin (TSP) were determined in 10 severely-ill Thai patients and 11 healthy volunteers. 8 patients recovered. At presentation, the platelet counts of the 10 patients were significantly lower (p < 0.025) than those of the controls, and a slight but significant increase (p < 0.05) in β-TG/PF4 ratios in the patients suggested low-grade platelet activation. Presentation plasma β-TG and PF4 concentrations did not differ from control values, probably due to the opposing effects of decreased circulating platelet mass and increased activation. By contrast, admission concentrations of TSP in the surviving patients were markedly lower (p < 0.001) than those of the controls; β-TG/PF4 ratios, but not TSP levels, returned to normal during treatment. Hepatic dysfunction and oliguric renal failure probably contributed to a sustained increase in plasma β - TG and TSP in the 2 fatally ill patients, but associated elevated PF4 levels indicated concomitant platelet activation. Our results support the suggestion that in vivo platelet activation, which appears to be rapidly controlled by treatment, occurs in patients with severe, non-fatal falciparum malaria. TSP production, apparently from non-platelet sources, was decreased and/or its consumption was increased in these patients, perhaps by factors such as cytoadherence of infected erythrocytes and consequent endothelial damage.     

Measurement of soluble C-type lectin-like receptor 2 in human plasma

Detection of platelet activation in vivo is useful to identify patients at risk of thrombotic diseases. Platelet factor 4 (PF4) and β-thromboglobulin (β-TG) are used for this purpose; however, they are easily released upon the minimal platelet activation that occurs during sampling. Soluble forms of several platelet membrane proteins are released upon platelet activation; however, the soluble form of C-type lectin-like receptor 2 (sCLEC-2) has not yet been fully investigated. Western blotting with an anti-CLEC-2 antibody showed that sCLEC-2 was released from washed human platelets stimulated with collagen mimetics. To detect sCLEC-2 in plasma, we established a sandwich enzyme-linked immunosorbent assay (ELISA) using F(ab′)2 anti-CLEC-2 monoclonal antibodies. Although plasma mixed with citrate, adenosine, theophylline and adenosine (CTAD) is needed for the PF4 and β-TG assays, effects of anti-coagulants (EDTA, citrate and CTAD) on the sCLEC-2 ELISA were negligible. Moreover, while special techniques are required for blood sampling and sample preparation for PF4 and β-TG assay, the standard blood collections procedures used in daily clinical laboratory tests have shown to suffice for sCLEC-2 analysis. In this study, we found that two forms of sCLEC-2 are released after platelet activation: a shed fragment and a microparticle-bound full-length protein, both of which are detected by the sCLEC-2 ELISA. The average concentration of sCLEC-2 in the plasma of 10 healthy individuals was 97?±?55?pg/ml, whereas that in the plasma of 25 patients with diabetes mellitus (DM) was 149?±?260?pg/ml. A trend towards an increase in sCLEC-2 concentration in the DM patients may reflect in vivo platelet activation in the patients, suggesting that sCLEC-2 may have clinical significance as a biomarker of in vivo platelet activation.     

Relationship of Platelet Specific Proteins and Other Factors to Atherosclerosis in Various Stages of Hypertension

There is considerable evidence from previous studies that platelets play an important role in the development and progression of atherosclerosis in hypertension, more so in relation to the stage of hypertension. Seventy one hypertensive patients (WHO stage I: 39, stage II: 23, stage III: 9) aged 19–84 (mean age: 56, normal controls in this study 59 and 62 respectively for each stage) and 37 aged 22-72 with a mean age of 52) were involved Hematocrit, beta-thromboglobulin (β-TG), platelet factor 4 (PF4), β-TG/PF4 ratio, total cholesterol (TC), low density lipoprotein-C, and triglycerides were higher in the hypertensive group while platelet count, circulating platelet aggregates, and high density lipoprotein-C were higher in the normotensive group. Among the hypertensives, stage I11 patients showed the highest β-TG, PF4, β-TG/PF4 ratio, triglycerides, and stage I with the least elevation. There were no significant differences noted in the ADP or epinephrine-induced platelet aggregation in both the normal and hypertensive patients. Other parameters such as heart rate, serum sodium, potassium, renal and liver function tests, plasma renin activity, aldosterone, fibrinogen thromboxane B and 6-Keto-PGF1jI showed no significant differences in both groups. This study clearly showed that β-TG/PF4 ratio and triglycerides are closely related to the stage of hypertension and are good indicators of in vivo platelet activation in hypertensives which may account for the acceleration of hypertensive vascular complications secondary to atherogenesis.     

Platelet factor 4 and β-thromboglobulin mRNAs in circulating microparticles of trauma patients as diagnostic markers for deep vein thrombosis

Deep vein thrombosis (DVT) is a common complication after trauma. The development of markers to predict DVT in trauma patients is needed, and circulating microparticles (MPs) and their contents are possible candidates. In this study, we aimed to identify platelet factor 4 (PF4) and β-thromboglobulin (β-TG) mRNAs in circulating MPs as potential markers for DVT diagnosis in trauma patients. Fifteen trauma patients diagnosed with DVT and fifteen matched patients without DVT were included in this study. Fifteen healthy volunteers also were included as controls. Circulating MPs were obtained from the plasma of all study subjects. Annexin V+?MPs and platelet-derived MPs (PMPs) were quantified using flow cytometry. PF4 and β-TG mRNAs in MPs were determined by qPCR, and the common logarithm of relative quantitation (RQ) was calculated using the comparative Ct method. Receiver-operating characteristic (ROC) curves were performed to analyze the diagnostic value of PF4 and β-TG mRNAs. No significant differences were found in Annexin V+?MPs and PMPs levels between trauma patients with and without DVT. However, both PF4 and β-TG mRNAs in MPs from the DVT group were significantly higher than the non-DVT group and healthy controls (P?=?0.014 for PF4, P?=?0.010 for β-TG). The ROC curve analysis showed that both the PF4 mRNA (area-under curve (AUC) 0.756, P?=?0.017) and the β-TG mRNA (AUC 0.751, P?=?0.019) had a positive predictive value for DVT. This finding indicates that the PF4 and β-TG mRNAs in MPs may be used as potential biomarkers for DVT diagnosis in trauma patients.

     

A prospective study of haemostatic parameters in relation to the clinical course of myeloproliferative disorders

Abstract: Platelet function and the clinical course of the disease were prospectively investigated in 29 patients with myeloproliferative disorders. Serial determinations (median: 5 investigations per patient within 17 months) of platelet aggregation, plasma and intraplatelet concentrations of β-thromboglobulin (βTG) and platelet factor 4 (PF4), and of fibrino-peptide A (FPA) plasma levels were carried out. In the chronic phase of polycythaemia vera, patients with thrombohaemorrhagic complications during the study period had higher platelet count, more severe platelet aggregation defects, and increased plasma levels of βTG and FPA compared to patients without complications. However, thrombohaemorrhagic complications were not predicted by changes in these parameters in the individual patient during the chronic disease phase. When patients with chronic myelogenous leukaemia entered blast crisis, bleeding complications were related to thrombocytopenia, impaired platelet function and low intraplatelet concentrations of βTG and PF4. Cytoreduction by chemotherapy in the chronic phase of CML did not alter βTG and PF4 plasma levels, whereas treatment of polycythaemia rubra vera by venesection favourably influenced platelet α-granule secretion and increased intraplatelet concentrations of βTG and PF4.     

Plasma concentrations of platelet-specific proteins correlated with platelet survival

Relationships between 51Cr platelet survival and plasma concentrations of beta-thromboglobulin (betaTG) and platelet factor 4 (PF4) were analyzed in 91 studies of patients with coronary artery disease. betaTG was significantly correlated with platelet life-span, turnover, and the number of hits in the multiple hit model. PF4 was significantly correlated with life-span and turnover. The most significant relationship involving platelet-specific protein concentrations and life-span estimates was between betaTG and life-span estimated using the multiple hit model (r = -0.39, p less than 0.001). There was a high correlation between betaTG and PF4 (r = 0.62, p less than 0.001), and no improvement could be obtained by combining the measurements of the two proteins in any regression with life-span or turnover. The results indicate that the patients with the shortest platelet survival time in this group tended to have the highest plasma concentration of betaTG and PF4 and thus probably increased in vivo release of betaTG and PF4. They strengthen the claim that these platelet-specific proteins may be indicators of platelet involvement in disease.     

Platelet factor 4 release during exercise in patients with coronary artery disease

Many recent studies provide evidence that increased platelet activation occurs in a significant number of patients with atherosclerotic coronary artery disease. The mechanisms responsible for this activation are unknown, although there have been studies suggesting a correlation with abnormal lipoproteinemia, acute myocardial infarction, unstable angina, and exercise-induced myocardial ischemia. We studied 84 patients undergoing standardized treadmill exercise using either a Bruce [N = 63] or symptom-limited Naughton protocol [N = 21]. In contrast to ten healthy volunteer subjects, the patient group demonstrated a significant increase in plasma concentrations of platelet factor 4 [PF4] between pre- and postexercise blood samples confirming earlier reports of exercise-induced platelet activation and secretion. As with previous studies, however, only a subset of patients demonstrated this response. When the entire group was analyzed for the presence or absence of electrocardiographic ischemic changes and the presence of documented versus suspected coronary artery occlusions, there were no differences noted between groups that explained the variable responses measured. However, there was a significant difference between patient groups when analyzed by whether or not they were being treated with β-blocking agents. Patients who were being treated with propranolol or one of the longer-acting β-blocking agents did not have a significant increase in plasma PF4 following exercise, in contrast to patients who were not β-blocked. Plasma concentrations of epinephrine, norepinephrine, and lactic acid were measured in 49 patients and all normal subjects. There was no correlation between the changes in plasma PF4 concentrations and any of these three variables, suggesting that platelet activation was not occurring through direct platelet activation by circulating catecholamines. This study provides further evidence that there is a subset of CAD patients with platelet hyperactivity. This is the first time that β-blockade has been demonstrated to modify this platelet response. The effectiveness of β-blocking agents in CAD may be in part related to their antiplatelet effect.     

Thrombocytopenia in early malaria is associated with GP1b shedding in absence of systemic platelet activation and consumptive coagulopathy

Thrombocytopenia develops early in malaria, but the underlying mechanisms remain incompletely understood. We studied the aetiology of malaria-associated thrombocytopenia in volunteers experimentally infected with Plasmodium falciparum malaria, in Indonesian malaria patients and in ex vivo studies. In experimental human malaria, the decrease in platelet counts was associated with a concurrent rise in young platelets (immature platelet fraction) and thrombopoietin. D-dimer concentrations were moderately elevated without a prolongation in the activated partial thromboplastin time or decrease in fibrinogen. There was no increase in expression of the platelet surface markers CD62P, PAC-1 and CD63 and in plasma concentrations of the platelet factors P-selectin, CXCR4, CXCL7, RANTES and CD40L. In contrast, concentrations of soluble glycoprotein-1b (sGP1b), the external domain of the platelet receptor for von Willebrand factor (VWF), increased early. Indonesian malaria patients also had elevated concentrations of sGP1b, which correlated with VWF concentrations. Finally, incubation of platelets with parasitized erythrocytes in vitro failed to induce platelet aggregation or activation. We concluded that neither compromised platelet production nor platelet activation or consumptive coagulopathy were responsible for the early thrombocytopenia in malaria. We hypothesize that the increase in sGP1b concentrations results from VWF-mediated GP1b shedding; a process that may prevent excessive adhesion of platelets and parasitized erythrocytes.     

Plasma concentration of platelet-specific proteins and fibrinopeptide A in patients with artificial heart valves

beta-Thromboglobulin (beta TG), platelet factor 4 (PF4), fibrinopeptide A (FPA), lactic dehydrogenase (LDH), and platelet count were evaluated in patients with bioprostheses and prosthetic heart valves. beta TG and PF4 were significantly elevated in both patient groups (p less than 0.001), whereas FPA was normal. There was no significantly difference in plasma concentrations of beta TG and PF4 between patients with prosthetic heart valves and bioprostheses. LDH levels were significantly (p less than 0.001) higher and platelet count lower (p less than 0.001) in patients with prosthetic cardiac valves. The data indicate that bioprostheses do not cause haemolysis or activation of the coagulation system. The findings that the plasma concentration of platelet-specific proteins were elevated, support the assumption that both types of valves cause platelet damage.     

Platelet secretory activities in acute malaria (Plasmodium falciparum) infection

During acute Plasmodium falciparum infection in man, plasma concentrations of platelet-specific proteins, beta-thromboglobulin (beta TG) and platelet factor 4 (PF4) were significantly elevated. For beta TG, the mean concentration was 136.24 +/- 71.58 ng/ml in patients, and 50.53 +/- 25.42 ng/ml in control subjects (t = 5.3794; p = 0.0001), while for PF4 mean values were, respectively, 75.35 +/- 23.09 and 18.64 +/- 13.42 ng/ml (t = -6.0897; p less than 0.0001). Platelet LDH loss in vitro in response to stimulation with 0.5 U of thrombin was 57.0 +/- 29.5% in patient samples and 24.8 +/- 16.9% (control); the values being significantly different from each other (t = 2.888; p less than 0.025). With serotonin (5HT) uptake and release however, the values were essentially normal, in spite of marginal difference observed in the uptake value of patients compared to control. The data indicate that there was in vivo platelet activation during the infection, with the haemostatic balance titled towards hypercoagulability. There was also associated easy platelet lysis with stimulation. It is also suggested that the latter finding may be one of the mechanisms of reduced circulating platelet numbers observed in patients in the acute disease.     

Dipyridamole and Platelet Release of Platelet-derived Growth Factor

Platelet-derived growth factor (PDGF) and β-thromboglobulin (β-TG) are released from platelet alpha-granules during platelet activation. PDGF is a potent chemoattractant and mitogen for human vascular smooth muscle cells, and may be important in the development of late restenosis following angioplasty and in atherogenesis. In recent studies, where PDGF release into serum was evaluated indirectly by measuring (3)H-thymidine incorporation into fibroblasts, it was reported that the antiplatelet drug dipyridamole (DPM) decreased serum levels of PDGF. Such selective inhibition of the PDGF-release would have potential important implications for patients with atherosclerosis and for patients undergoing angioplasty. We therefore measured platelet content of PDGF and β-TG as well as platelet release of PDGF using a newly developed radioimmunoassay in healthy volunteers before and immediately after ingestion of DPM 100 mg t.i.d. for 3 days. We found no significant differences in platelet content of PDGF or β-TG before and after DPM. PDGF release from platelets isolated from plasma by gel filtration and stimulated with thrombin as well as platelet release of PDGF into serum was also unaffected by DPM. In conclusion, treatment with DPM does not affect platelet content of PDGF or β-TG. The treatment did not inhibit the platelet-release of PDGF as previously reported, neither via direct effects on platelets nor on inhibitory plasma components. DPM may, however, inhibit (3)H-thymidine incorporation into fibroblasts.     

Heparin-releasable platelet factor 4 in patients with coronary artery disease.

Recently, platelet factor 4 (PF4) release by heparin (heparin-releasable PF4) has been examined as a useful marker of the interaction between the substances liberated from circulating platelets and the vascular endothelium. We compared the plasma levels of PF4 and beta-thromboglobulin (beta-TG) after intravenous heparin injection in patients with coronary artery disease (CAD) and normal control subjects. We also studied the effects of low-dose aspirin (81 mg/day) on the plasma level of heparin-releasable PF4 in the CAD patients. Blood samples were obtained before and 5 min after the intravenous injection of heparin (1,000 IU) from 23 patients with CAD and 15 normal control subjects. Although the plasma beta-TG level remained unchanged after heparin injection, the plasma PF4 level markedly increased in both groups. There was a significant difference in plasma PF4 levels at 5 min after heparin injection between the CAD group (100.1 +/- 38.1) and the control group (61.0 +/- 24.0) (p less than 0.01). The PF4/beta-TG ratio after heparin injection was also higher in the CAD group than in the control group (p less than 0.01). There was a correlation between the PF4/beta-TG ratio after heparin and the Gensini CAD score, which defines the severity of coronary atherosclerosis (r = 0.489, n = 23, p less than 0.01). Low-dose aspirin was administered to 11 CAD patients for 246.0 +/- 28.8 days. Blood samples for the assay of PF4 and beta-TG were obtained as stated above, and platelet aggregation, thromboxane B2 (TxB2), and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) levels were also measured before and during aspirin administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence against enhanced platelet activity in sickle cell anaemia

S ummary . Although numerous studies have provided indirect evidence for enhanced platelet activity in sickle cell anaemia, little attention has been directed to examination of platelet alpha and dense granule release in the sickling disorders. We simultaneously measured by radioimmunoassay plasma levels of the alpha granule constituents β-thromboglobulin (β-TG) and platelet factor 4 (PF₄) in 43 children with sickle cell anaemia in steady state and 24 patients during severe vaso-occlusive crisis. β-TG levels during steady state (50 ± 3.6 ng/ml, mean ± SEM) were greater ( P <0.001) than in normal controls (36 ± 1.6), but there was no additional significant rise during crisis (55 ± 5.9). PF₄ levels were similar ( P = 0.12) in both steady state (10 ± 1.2 ng/ml) and crisis (9.3 ± 2.3) to those of normal controls (6.0 ± 0.8). The similarity of β-TG/PF₄ ratios in normal and sickle cell anaemia patients as well as the positive correlation ( P <0.05) between platelet count and β-TG and PF₄ suggested that an artefactual in vitro platelet activation was responsible for some of the observed increased β-TG and PF₄ levels. Further evidence against enhanced platelet activity in these sickle cell patients included normal intraplatelet content of the dense granule constituent 5-HT and a normal ATP/ADP ratio. From this data we conclude that platelet activation in children with sickle cell anaemia appears minimal.     

Platelet factor-4 excretion in myeloproliferative disease: implications for the aetiology of myelofibrosis

S ummary. Experimental evidence suggests that the fibroblastic proliferation often associated with the myeloproliferative disorders is not part of the neoplastic process, but is secondary to an unknown stimulus. This stimulus may be a factor derived from platelets which promotes the proliferation of fibroblasts in vitro (PDGF). Plateletderived growth factor is localized to platelet α-granules together with PF4 and β-TG. As an indicator of α-granule release, we have measured PF4 levels in plasma. platelets and urine in 46 normal subjects and 49 patients with myeloproliferative disorders, secondary thrombocytosis and miscellaneous malignancies. All 11 patients with elevated urinary PF4 excretion exhibited myelofibrosis, whereas 11 of 22 patients with documented myelofibrosis had urinary PF4 excretion in the normal range. No correlation was seen between marrow fibrosis and plasma levels or the platelet content of PF4. The data are consistent with the possibility that release of mitogen(s) from platelet or megakaryocyte α-granules in some patients with myeloproliferative disorders is pathogenetically related to the development of marrow fibrosis.     

Platelets are not hyperreactive in patients with ovarian cancer

Paraneoplastic thrombocytosis has been reported in different types of solid tumors, including ovarian epithelial cancer, and found to be associated with a worse outcome. Although the effect of cancer on increasing platelet counts is well documented, the effect of cancer on platelet functions is not well known. We compared in vitro aggregation response of platelets isolated from 34 patients with ovarian cancer to those of platelets from 19 patients with benign ovarian tumors. Aggregation studies were conducted in a light transmission aggregometer, using both a high and a low dose of ADP and collagen. We evaluated platelet preactivation by measuring the plasma concentration of β-thromboglobulin (β-TG) and platelet factor-4 (PF-4) as markers of platelet α granule secretion, using ELISA. We found that ovarian cancer is not associated with an enhanced aggregation response of platelets to ADP or collagen, and plasma concentration of β-TG and PF-4 is not higher in patients with ovarian cancer compared to those in patients with benign ovarian tumors.     

Human platelet factor 4: Preparation from outdated platelet concentrates and application in cerebral vascular disease

Platelet factor 4 (PF4), the platelet antiheparin protein, was isolated from both the supernatant and the cells of recently outdated platelet concentrates. Following purification by affinity chromatography, a competitive binding radioimmunoassay was developed to detect this protein in human plasma. The normal range was determined to be 9.4 ± 4.7 ng/ml (mean ± SD for 52 healthy adults). In order to determine whether individuals with transient ischemic attack (TIA) or stroke had measurable increments of PF4 in their plasma, radioimmunoassay studies were performed on 11 patients with well-documented TIA, 10 patients with well-documented stroke and on 16 age-matched controls hospitalized on a neurology service with disorders unrelated to arterial thrombosis. The 16 hospitalized controls had PF4 levels of 10.3 ± 9.1 ng/ml, a value not significantly different from the 52 normals (P > 0.50). Patients with TIA had PF4 levels of 24.6 ± 12.1 ng/ml, a value significantly higher than both the 52 normals (P < 0.001) and the 16 hospitalized control patients (P < 0.005). Patients with stroke had PF4 levels of 35.4 ± 29.2 ng/ml, a value significantly higher than both the 52 normals (P < 0.001) and the 16 hospitalized control patients (P < 0.005). Outdated platelet concentrates facilitate the development of a reproducible radioimmunoassay for PF4. The elevation of this platelet-derived protein in the plasma of patients with stroke and TIA provides evidence for recent or ongoing platelet activation in the cerebral vascular disease population.     

The immediate effect of aerobic exercise on haemostatic parameters in patients with recently diagnosed mild to moderate essential hypertension

Background Exercise is frequently recommended for the treatment of patients with arterial hypertension. Previous studies have shown an enhanced coagulation state after exercise. Our study investigates the alterations observed after a single session of submaximal aerobic exercise concerning coagulation, fibrinolysis, platelet activation as well as endothelial function in patients with recently diagnosed essential hypertension. Methods Twenty non-diabetic patients with recently diagnosed essential hypertension participated in a 45 min submaximal exercise test on a bicycle ergometer. Blood samples were drawn before and after exercise in order to determine parameters of coagulation activation (Prothrombin time [PT], activated Partial Thromboplastin time [aPTT], fibrinogen, D-Dimers, prothrombin fragments 1 + 2 [PF1+2], thrombin-antithrombin III complex [TAT] and factors VII, VIII and XII), platelet activation (Platelet count, Platelet factor 4 [PF4] and β-thromboglobulin [β-TG]), fibrinolysis activation (Plasmin-a₂ antiplasmin complex, PAP) and endothelial function (soluble Thrombomodulin [sTM] and von Willebrand factor [vWf]). Soluble P-selectin served as a marker for endothelial and platelet activation. Results All patients completed the exercise test. aPTT (P < 0.001) and factor VII (P = 0.01) significantly decreased while PT (P = 0.04), fibrinogen (P = 0.008), factor VIII (P < 0.001), platelet count (P = 0.002) and β-TG levels (P = 0.01) significantly increased as a result of exercise. Compared to baseline there was an 11% increase in TAT (P = 0.04) and a 28% increase in PAP (P < 0.001) at peak exercise. One hour post exercise, there was a 43% increase in PAP whereas TAT levels became similar to those at baseline. Additionally vWf (P = 0.01) and sP-selectin (P = 0.02) levels significantly increased throughout the exercise protocol. Conclusions Patients with recently diagnosed and never treated mild to moderate essential hypertension undergoing submaximal aerobic exercise present evidence of enhanced fibrinolysis compared with a mild increase of coagulation indices. However, whether there is a favourable effect of exercise on fibrinolysis over coagulation and/or endothelial involvement during exercise needs to be further investigated.     

In Vivo Platelet Hyperactivity and Factor VIII Related Antigen Increase Long after Myocardial Infarction

In the Anturane Reinfarction Italian Study the trend of some specific and quantitative haemostatic parameters is being investigated in different series of patients balanced for sulfinpyrazone and placebo. In a series of young male patients who had had myocardial infarction 6 months previously, it has been shown that the placebo treatment subsample presented shortened platelet production time (PPT), increased levels of plasma β-thrombo-globulin (β-TG) and platelet factor 4 (PF₄), and increased factor VIII related antigen (VIII:RAg) compared with a matched control group. A close correlation between plasma concentration of VIILRAg and PPT was evidenced in the same treatment subsample. The sulfinpyrazone treatment subsample presented normalized PPT accompanied by reduction of VIII:RAg but not of β-TG or PF₄ levels.     

Elevated plasma levels of beta-thromboglobulin and platelet factor 4 in patients with rheumatic disorders and cutaneous vasculitis

The efficacy of plasma levels of β-thromboglubulin (β-TG) and platelet factor 4 (PF4) as markers of the presence and activity of vasculiditic processes in rheumatic diseases were evaluated, first by serial measurement of their levels in a patient with rheumatoid arthritis and a chronic leg ulcer in the course of treatment, and second in 11 patients with rheumatoid arthritis without cutaneous vasculitis, and in nine patients with a variety of rheumatic diseases with cutaneous vasculitis. In the former, plasma levels of β-TG and PF4 were elevated and slowly reduced in parallel with healing, raised again after relapse, and normalized after disappearance of the leg ulcer. In the latter, both plasma levels were elevated in all of the nine patients with cutaneous vascular lesions and in one of the 11 patients rheumatoid arthritis without skin lesions. Levels of β-TG and PF4 may be useful to estimate the presence of vascular lesions in rheumatic disorders. Received: 5 November 2001 / Accepted: 18 June 2002 Correspondence and offprint requests to: Dr Toshihide Yamamoto, Kishiwada Tokushukai Hospital, 4-22-38 Isonokami-cho, Kishiwada, Osaka 596-0001, Japan. Tel: 81-724-38-8781; Fax: 81-724-37-7395; E-mail: ikyoku@kishiwada.tokushukai.or.jp     

Platelet Activation in Response to Phlebotomy

ABSTRACT. Plasma concentrations of β-thromboglobulin (BTG) and platelet factor 4 (PF4) were measured in three consecutive blood samples from 29 healthy male blood donors. The first sample was collected after 15 min of rest, the second immediately after a phlebotomy of 450 ml blood and the third after a further 15 min of rest. The mean baseline plasma BTG and PF4 values were 68 × 5 and 13.8 ± 0.7 ng/ml, respectively. The second sample's mean plasma values of these two platelet-specific proteins were significantly higher (88 ± 9 and 24.1 ± 4.1 ng/ml, respectively). The plasma concentrations of BTG and PF4 in the last sample, however, had returned to baseline levels. It is concluded that significant but short-lasting platelet activation and secretion take place in healthy subjects in response to an acute but comparatively mild blood loss even though the platelets do not participate in the process of hemostasia.