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)     

Plasma beta-thromboglobulin values in thrombocytopenic patients with acute leukemia

Plasma beta-thromboglobulin (beta-TG) levels were measured in 14 healthy subjects and in 20 acute leukemia (AL) patients, newly diagnosed, with highly variable values for venous platelet counts. For healthy subjects the plasma beta-TG levels ranged 12-38 (mean 17) ng/ml. In this group of patients with AL, a highly significant positive correlation (P < 0.001) between the values for plasma beta-TG and venous platelet count was present. During a thrombocytopenic period, the plasma beta-TG concentraton was measured in nine of the AL patients immediately before and 10 to 12 hours after platelet transfusion therapy. Fourteen platelet transfusions were administered when the patient's highest temperature of the day was < 38.5 degrees C, and 18 when the highest temperature of the day was greater than or equal to 38.5 degrees C. The mean pre-transfusion and post-transfusion beta-TG values for the 14 platelet transfusions were 7 +/- 2 and 20 +/- 5 ng/ml, respectively. The corresponding means for the 18 transfusions given to febrile patients were 5 +/- 2 ng/ml and 11 +/- 2 ng/ml, respectively. Of the pretransfusion values, 11/14 and 14/18 were below the control range. We conclude that the plasma beta-TG values are considerably lower in thrombocytopenic patients than in subjects with normal platelet counts. Further work should provide reference values for plasma beta-TG over a wide range of venous platelet counts.     

Augmented platelet reactivity and thromboxane A2 production possible aggravating factors in unstable angina

We examined platelet aggregation and plasma levels of thromboxane B2, a stable metabolite of thromboxane A2, in patients with unstable angina and correlated these platelet indices with the response to antianginal conventional therapy such as isosorbide dinitrate and calcium channel blocker. Eight of 36 patients exhibited anginal attacks more than 5 times/week in spite of the therapy, designated refractory unstable angina, associated with augmented platelet aggregation induced by arachidonate (0.3 mM, 71 +/- 3%, mean +/- SEM) and collagen (2 micrograms/ml, 72 +/- 5%), and elevated plasma levels of thromboxane B2 (350 +/- 19 pg/ml). In the remainder of the patients whose anginal attacks were effectively subsided by the therapy, platelet aggregation was much lower (arachidonate: 34 +/- 9%, collagen: 31 +/- 8%, p less than 0.01) and plasma levels of thromboxane B2 were also lower (295 +/- 12 pg/ml, p less than 0.05). To evaluate the effect of selective thromboxane A2 blockade on clinical findings and platelet reactivity in refractory unstable angina, OKY-046 (600 mg/day, p.o.) was administered to another 14 patients with refractory unstable angina in addition to the conventional therapy. We found that platelet aggregation induced by arachidonate (71 +/- 4%) and collagen 65 +/- 8%) was markedly reduced (44 +/- 7% and 24 +/- 3%, respectively, p less than 0.01) and plasma levels of thromboxane B2 (358 +/- 31 pg/ml) and thromboxane B2 production in serum (29 +/- 5 ng/ml) were also significantly reduced after OKY-046 treatment (262 +/- 21 pg/ml, p less than 0.05, and 1.4 +/- 0.2 ng/ml, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Defective platelet aggregation and increased platelet turnover in patients with myelofibrosis and other myeloproliferative diseases

In 9 patients with myeloproliferative diseases (MPD) (6 with myelofibrosis, MF, 1 with Ph1 positive chronic granulocytic leukaemia, CGL, 1 with primary eosinophilia, PE, 1 with pre-leukaemia syndrome, preL) collagen, epinephrine, and ADP-induced aggregation, N-ethylmaleimide-induced malondialdehyde (MDA) production, beta-thromboglobulin (beta-TG) plasma levels, and platelet turnover were studied. Collagen-induced aggregation was found to be normal in 7 patients, absent in 1, and reduced in 1. In all but 3 patients, aggregation with ADP was markedly reduced. Epinephrine-induced aggregation was decreased in 7 patients. No difference was found between mean MDA production in MPD (3.21 +/- 0.50 nmol/10(9) PLTs) and in control group of 21 normal subjects (3.04 +/- 0.26 nmol/10(9) PLTs). Mean beta-TG levels were significantly higher (P less than 0.01) in MPD patients (165.00 +/- 28.29 ng/ml) than in healthy controls (81.76 +/- 14.63 ng/ml). Mean platelet production half-time was significantly shorter in MPD (2.48 +/- 0.24 d) than in the control group (3.43 +/- 0.17 d), after adjustment for age by covariance analysis (P less than 0.005). Our data do not indicate an abnormal prostaglandin synthesis and are consistent with the hypothesis that a disseminated intravascular platelet aggregation might take place in MPD patients.     

Platelet activation during thrombolysis and percutaneous transluminal coronary angioplasty in the acute phase of myocardial infarction

To clarify the mechanism of recanalization and reocclusion in thrombolysis and percutaneous transluminal coronary angioplasty (PTCA), the plasma concentrations of beta-thromboglobulin (beta-TG), thromboxane B2 (TXB2) and platelet aggregation adenosine diphosphate (ADP) (2 microM/ml, collagen 2 micrograms/ml) were assessed in 11 normal subjects and in 19 patients with acute myocardial infarction whose infarct-related vessels were recanalized by thrombolysis and/or PTCA. In patients with acute myocardial infarction, the plasma concentrations of beta-TG and TXB2 were significantly higher than those in normal subjects (beta-TG: 128 +/- 132 ng/ml vs 38 +/- 17 ng/ml, TXB2: 131 +/- 154 pg/ml vs 36 +/- 18 pg/ml). Collagen-induced platelet aggregation decreased significantly in patients with acute myocardial infarction; whereas, ADP-induced platelet aggregation showed no significant difference. Infarct-related vessels recanalized by thrombolysis (seven patients: group 1) and PTCA (seven patients: group 2) were patent on the follow-up angiograms. Infarct-related vessels were reoccluded in five patients immediately after PTCA or during the follow-up angiography (group 3). Beta-TG and TXB2 did not change before and after recanalization in groups 1 and 2, but increased significantly after recanalization in group 3 (beta-TG: 155 +/- 185 ng/ml----269 +/- 233 ng/ml, TXB2: 104 +/- 87 pg/ml----169 +/- 91 pg/ml). Platelet aggregation did not differ significantly among the three groups. We concluded that platelets are not activated during thrombolysis and/or PTCA in cases without reocclusion, while platelets are markedly activated during PTCA in cases with reocclusion. Thus, it is suggested that platelet activation plays an important role in the mechanism of reocclusion.     

Increased blood coagulation and platelet activation in patients with infective endocarditis and embolic events

BACKGROUND: Inflammation-induced procoagulant changes and alterations in platelet activity appear to play an important role in thromboembolic complications of infective endocarditis (IE). HYPOTHESIS: The aim of this study was to investigate systemic coagulation activity, fibrinolytic capacity, and platelet activation in patients with IE with and without embolic events by measuring the plasma levels of prothrombin fragment 1+2 (PF1+2), thrombin-antithrombin III complex (TAT), plasminogen activator inhibitor-1 (PAI-1), beta-thromboglobulin (beta-TG), and platelet factor 4 (PF4), respectively. METHODS: The study included 76 consecutive patients (female = 55, male = 21, mean age 26 years, range 8-64 years) with definite IE according to the Duke criteria; of these, 13 (17.1%) had embolic events. RESULTS: Plasma concentrations of PF1+2 (3.2 +/- 1.3 vs. 1.7 +/- 0.7 and 1.4 +/- 0.7 nmol/l, p < 0.001, respectively) and TAT (7.3 +/- 1.5 vs. 2.9 +/- 1.2 and 2.2 +/- 1.1 ng/ml, p < 0.001, respectively) were elevated in patients with embolic events compared with patients without embolic events and control subjects. Similarly, patients with embolic events had increased plasma levels of beta-TG (63.3 +/- 10.9 vs. 33.1 +/- 11.6 and 19.1 +/- 10.6 ng/ml, p < 0.001, respectively) and PF4 (106.0 +/- 28.7 vs. 50.3 +/- 16.7 and 43.0 +/- 15.8 ng/ml, p < 0.001, respectively) compared with those without embolic events and the control group. Embolic patients also had higher PAI-1 levels than nonembolic patients and healthy subjects (14.4 +/- 6.4 vs. 8.6 +/- 5.9 and 5.4 +/- 4.3 ng/ml, p = 0.002, respectively). CONCLUSION: Patients with IE and with subsequent thromboembolism have increased systemic coagulation activation, enhanced platelet activity/damage, and impaired fibrinolysis. The resulting imbalance produces a sustained hypercoagulable state, which contributes to the increased risk of thromboembolic events in this particular group.     

Platelet dysfunction and alteration of prostaglandin metabolism after chronic alcohol consumption

To study the effects of chronic alcohol consumption on platelet functions, the rate of arachidonate-induced platelet aggregation, the production of malondialdehyde in platelets, and plasma levels of prostaglandin endoperoxide metabolites were examined in 88 chronic alcoholics and 24 healthy controls. The rate of platelet aggregation and the production of malondialdehyde in platelets were greater in chronic alcoholics both on admission and 1 week after. However, these alterations returned to the level of healthy controls within 4 weeks of abstinence from alcohol and were independent of the number of circulating platelets. Furthermore, on admission, plasma levels of thromboxane B2 were significantly increased in chronic alcoholics when compared with those of healthy controls (400.8 +/- 36.5 versus 241.7 +/- 28.9 pg/ml plasma; p less than 0.025) and were also significantly correlated with malondialdehyde production in washed platelet debris (r = 0.6049; p less than 0.001). In contrast, plasma levels of 6-keto prostaglandin F1 alpha and prostaglandin E were not altered after chronic alcohol consumption. As a result, the ratio of 6-keto prostaglandin F1 alpha to thromboxane B2 was markedly decreased in chronic alcoholics (0.31 +/- 0.03 versus 0.62 +/- 0.13; p less than 0.001). These results strongly suggest that the imbalance in prostaglandin endoperoxide metabolites is produced by chronic alcohol ingestion. Moreover, a significant correlation was observed between platelet aggregation rate and malondialdehyde production during platelet aggregation (r = 0.559; p less than 0.005). Thus, we conclude that chronic alcohol consumption alters platelet thromboxane metabolism, which is likely associated with the increased ability of platelets to aggregate.     

A prospective study of G-CSF effects on hemostasis in allogeneic blood stem cell donors.

Granulocyte colony-stimulating factor (G-CSF) is used in healthy donors of peripheral blood stem cells (PBSC) for allogeneic transplantation. However, some data have recently suggested that G-CSF may induce a hypercoagulable state, prompting us to study prospectively 22 PBSC donors before and after G-CSF 5 microg/kg twice daily. We sought evidence for changes in the following parameters: platelet count, von Willebrand factor antigen (vWF:Ag) and activity (vWF activity), beta-thromboglobulin (beta-TG), platelet factor 4 (PF-4), platelet activation markers (GMP-140 and PAC-1), activated partial thromboplastin time (aPTT), prothrombin time (PT), coagulant factor VIII (FVIII:C), thrombin-antithrombin complex (TAT), prothrombin fragment 1+2 (F1+2), thrombomodulin (TM) and tissue plasminogen activator antigen (tPA:Ag) prior to G-CSF and immediately before leukapheresis. ADP-induced platelet aggregation studies were also performed. G-CSF administration produced only mild discomfort. We found a significant increase in vWF:Ag (from 0.99 +/- 0.32 U/ml to 1.83 +/- 0.69 U/ml; P < 0.001), in vWF activity (from 1.04 +/- 0.34 U/ml to 1.78 +/- 0.50 U/ml; P < 0.001) and in FVIII:C (from 1.12 +/- 0.37 U/ml to 1.73 +/- 0.57 U/ml; P < 0.001) after G-CSF. Of note, four donors with low baseline vWF had a two- to three-fold increase after receiving G-CSF. G-CSF had no impact on the platelet count, beta-TG, PF-4, GMP-140 or PAC-1. The final% of platelet aggregation decreased from 73 +/- 22% to 37 +/- 26% after G-CSF (P < 0.001). We found a significant decrease in aPTT after G-CSF (29.9 +/- 3.1 s to 28.3 +/- 3.3 s; P = 0.004), but the PT was unaffected. In addition, we also observed a significant increase in TAT, F1+2 and TM, but not in tPA:Ag. Our data suggest that G-CSF may possibly induce a hypercoagulable state by increasing levels of FVIII:C and thrombin generation. In contrast to this information, we found reduced platelet aggregation after G-CSF administration. The clinical implications of these findings remain unclear and larger studies are definitely required.     

Increased platelet activity in patients with isolated coronary artery ectasia

BACKGROUND: The common coexistence with coronary artery disease has led to the suggestion that coronary artery ectasia (CAE) is a variant of coronary artery disease. The mechanisms, however, responsible for CAE formation during the atherosclerotic process and the exact clinical significance are not well known. In this study, we aimed to investigate platelet activity in patients with isolated CAE by using specific markers of platelet activation as P-selectin, beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4). METHODS: Thirty-two patients with isolated CAE without significant stenosis and 30 control participants with angiographically normal coronary arteries were included in this study. According to the angiographic definition used in the Coronary Artery Surgery Study, a vessel is considered to be ectasic when its diameter is > or = 1.5 times that of the adjacent normal segment in segmental ectasia. Plasma P-selectin, beta-TG and PF4 levels were measured in all patients and control participants using enzyme-linked immunosorbent assay method. RESULTS: Patients with isolated CAE were detected to have significantly higher levels of plasma P-selectin, beta-TG and PF4 in comparison with control participants with angiographically normal coronary arteries (P-selectin: 248+/-46 vs. 154+/-32 ng/ml, respectively, P<0.001; beta-TG: 51+/-19 vs. 21+/-9 ng/ml, respectively, P<0.001; PF4: 58+/-23 vs. 33+/-11 ng/ml, respectively, P<0.001). CONCLUSION: In conclusion, we have shown for the first time that patients with isolated CAE have raised levels of plasma P-selectin, beta-TG and PF4 compared with control participants with angiographically normal coronary arteries, suggesting increased platelet activation in patients with CAE.     

Effects of acute smoking on the hemostatic system in humans

Habitual smoking is one of the best established risk factors for cardiovascular disease. The pathogenesis of smoke-induced damage is not so well clarified, but it probably includes--among some other aspects--an activation of the hemostatic system. Recently it has been shown that smoking a single cigarette can significantly decrease the coronary blood flow in coronary patients as well as in normal subjects. We tested the hypothesis that the acute effects of smoke are mediated by the hemostatic system. Seven healthy male volunteers, aged 20-40 years (mean 32 +/- 6 years), entered the study. All were habitual smokers, but had abstained from smoking in the 12 hours preceding the test. After lying in absolute rest for about 30 minutes, each subject smoked a cigarette containing 1.2 mg of nicotine. Immediately before and after smoking, blood was drawn by clear venipuncture for the evaluation of the following hemostatic variables: collagen-induced platelet aggregation by the method of Born; thromboxane B2 (TxB2) production by platelets stimulated with collagen, radioimmunoassay (RIA); plasma beta thromboglobulin (TG) (RIA); plasma fibrinopeptide A (FPA) (RIA); plasma fibrinolytic activity in the euglobulin fraction (NEF) (fibrin plate method). The following results, respectively before and after smoking, were observed: collagen-induced platelet aggregation 55 +/- 3 vs. 57 +/- 6%; TxB2 100.5 +/- 5.9 vs. 90.3 +/- 9.0 ng/10(8) platelets; plasma beta-TG 20.8 +/- 2.2 vs. 19.2 +/- 2.3 ng/ml; plasma FPA 2.3 +/- 0.3 vs. 2.2 +/- 0.1 ng/ml; NEF, lysis diameter 16.8 +/- 1.6 vs. 16.7 +/- 1.7 mm; NEF + C1 inhibitor lysis diameter 8.8 +/- 0.7 vs. 9.1 +/- 0.7 mm.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma beta-thromboglobulin and platelet factor 4 concentrations in patients with atrial fibrillation

The clinical significance of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF-4) levels were evaluated in 26 patients with atrial fibrillation (af) complicated by valvular heart disease (VHD), 73 patients with af but without valvular heart disease and 57 normal subjects. The beta-TG level was significantly higher in af patients without VHD than in normal subjects (49.4 +/- 35.8 ng/ml vs 31.2 +/- 14.0 ng/ml, p less than 0.01) and in af patients with VHD than in normals (64.1 +/- 52.8 ng/ml vs 31.2 +/- 14.0 ng/ml, p less than 0.01). Af patients with or without VHD tended to show high levels of PF4 compared with normals (af patients without VHD: 34.1 +/- 45.5 ng/ml, af patients with VHD: 18.6 +/- 27.2 ng/ml, normals: 11.6 +/- 8.2 ng/ml). There was no correlation between beta-TG levels and age in af patients without VHD or in normals. There was also no correlation between beta-TG levels and heart rate in af patients without VHD. The activation of platelets was suggested in patients with atrial fibrillation on the basis of increased levels of platelet releasing substances, especially in those with VHD. The high levels of beta-TG and PF4 in patients with atrial fibrillation may be one explanation for the high incidence of thromboembolism in these patients, indicating the necessity of antiplatelet therapy.     

Sustained-release nifedipine (nifedipine-L) suppresses plasma thromboxane B2 and 6-keto prostaglandin F1 alpha in both young male smokers and nonsmokers

Sustained-release nifedipine (nifedipine-L) (40 mg twice a day) was administered orally to healthy young adult male smokers and nonsmokers for 10 days, and its effects on platelet aggregation, beta-thromboglobulin and platelet factor 4 levels, and plasma thromboxane B2 (TxB2) and 6-ketoprostaglandin F1 alpha (6-Keto-PGF1 alpha) concentrations were studied. The plasma nifedipine-L concentration in smokers (46.0 +/- 7.4 ng/ml) was significantly lower than that in nonsmokers (88.2 +/- 1.2 ng/ml). Nifedipine-L did not affect platelet aggregation induced by adenosine diphosphate, collagen, or epinephrine in either smokers or nonsmokers. The plasma beta-thromboglobulin level on the tenth day of nifedipine-L administration in nonsmokers was lower than that in smokers, but there were no significant differences either with or without nifedipine-L or between nonsmokers and smokers. Nifedipine-L had no effect on the concentration of platelet factor 4 in either smokers or nonsmokers. On the other hand, nifedipine-L significantly decreased the plasma TxB2 and 6-keto-PGF1 alpha concentrations in both smokers and nonsmokers. Thus we concluded that nifedipine-L suppressed the production of plasma TxB2 from platelets and also subsequently suppressed the production of 6-keto-PGF1 alpha and that this action was not affected by cigarette smoking.     

Plasma levels of beta-thromboglobulin and platelet factor 4 in relation to the venous platelet concentration

The plasma levels of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF-4) were determined in patients with various hematologic malignancies, and the results were related to simultaneously determined venous platelet counts. All studied patients were in a steady state. The plasma beta-TG concentrations were determined on 69 occasions and the values ranged from 0 to 82 ng/ml. In 33 instances, the venous platelet count was <25 x 10 (9/1) and in two thirds of these samples beta-TG was undedectable. The highest values for plasma beta-TG were found in patients with the highest venous platelet counts. A highly significant correlation (r=0.77, p <0.001) between the values for plasma beta-TG and venous platelet count was present. The plasma concentrations for PF-4 ranged from 0 to 50 ng/ml. Similarly, there was a highly significant relationship (r=0.78, p<0.001) between the values for PF-4 and venous platelet concentration. We conclude, if the plasma levels of beta-TG and PF-4 are used as markers of platelet activation in vivo, it is necessary to simultaneously consider the platelet concentration in the collected blood.     

The effects of trapidil on left ventricular function and platelet aggregation in patients with coronary artery disease subjected to pacing.

The effects of the intravenous administration of 100 mg of trapidil on systolic and diastolic left ventricular functions and coronary sinus blood flow, as well as on myocardial lactate metabolism and platelet aggregation, were investigated before and after pacing in 12 patients with coronary artery disease. Pacing without administration of trapidil provoked angina in 6 of these patients. During rest, trapidil decreased the mean blood pressure by an average of 5 mmHg (from 112 +/- 15 to 107 +/- 8 mmHg, p less than 0.05) and the left ventricular end-diastolic pressure by an average of 4 mmHg (from 10 +/- 3 to 6 +/- 2 mmHg, p less than 0.05). Trapidil also caused both the max dp/dt and the coronary sinus blood flow to increase slightly, although it had no significant effect on diastolic function, myocardial lactate metabolism, or platelet aggregation. During the pacing that followed trapidil administration, chest pain was not provoked in the same 6 patients who had previously experienced chest pain on pacing. The extent of ST-segment depression also improved from -1.6 +/- 0.3 to -0.9 +/- 0.7 mm (p less than 0.05) and there was a significant suppression of the production of myocardial lactate. When pacing was terminated, trapidil caused a decrease in left ventricular systolic pressure from 173 to 156 mmHg (p less than 0.05), and also caused a decrease of the left ventricular end-diastolic pressure, from 16 +/- 4 to 8 +/- 2 mmHg (p less than 0.05). Trapidil had no significant effect on platelet aggregation activity with either a 1 microM or a 2 microM dose of ADP (adenosine diphosphate). However, the beta-TG level was suppressed, decreasing from 119 +/- 14 to 99 +/- 19 ng/ml in the arterial blood (p less than 0.1) and from 114 +/- 9 to 103 +/- 17 ng/ml (p less than 0.1) in the coronary sinus blood. Reductions in the preload and afterload by trapidil were of far greater magnitude than either its coronary dilatory or positive chronotropic effects in patients with coronary artery disease. Thus trapidil, a new antianginal agent appears to inhibit the production of platelet derived growth factors and may, therefore, protect the arteries from atherosclerosis as it promotes beneficial systemic hemodynamics in patients with depressed ventricular function.     

Evidence that platelet density depends on the alpha-granule content in platelets

The relation between platelet buoyant density and beta-thromboglobulin (beta-TG), a marker for platelet alpha-granule content, was assessed by three independent approaches. (1) Platelets were separated on iso- osmolar discontinuous Stractan density gradients into five fractions, ranging in density from 1.061 g/ml to 1.091 g/ml (20 degrees C). The beta-TG content (mean +/- SD, n = 17) increased with the platelet density from 27.8 +/- 8.6 micrograms beta-TG/10(9) cells (20% less- dense platelets) up to 65.6 +/- 15.5 micrograms beta-TG/10(9) cells (15% most-dense platelets). (2) Activation of platelets in platelet- rich plasma with thrombin, adenosine diphosphate, collagen, or epinephrine resulted in a decreased density of the platelets. This was only seen when there was simultaneous secretion of beta-TG. (3) The less-dense and the more-dense platelet fractions, after isolation by density gradient centrifugation, were separately treated with thrombin. After complete degranulation, the density distribution of the originally less-dense and more-dense platelets were identical and were much narrower than the density distribution of resting platelets.     

Platelet aggregation and coagulation factors in insulin dependent diabetics with and without microangiopathy

Abnormalities of platelet aggregation and coagulation have been reported in insulin dependent diabetes mellitus (IDDM), although there is controversy concerning their relationship to microangiopathy. We have studied platelet function and haemostasis in 55 patients with IDDM, 23 without, 14 with mild (background retinopathy) and 18 with severe (proliferative retinopathy, or background retinopathy plus proteinuria) complications. Studies were done on 2 occasions 8 weeks apart and the results compared with 28 control subjects. There was evidence of increased in vivo platelet aggregation in the diabetic group v controls shown by raised values of beta-thromboglobulin (61 +/- 42, mean +/- SD, v 18 +/- 14 micrograms/ml, p less than 0.001), platelet factor 4 (62 +/- 76 v 14 +/- 11 micrograms/ml, p less than 0.01), and platelet micro-aggregates (20 +/- 16 v 12 +/- 11%, p less than 0.01). There was no significant difference in fibrinogen and fibrinopeptide A levels, nor in 'in vitro' tests of platelet aggregation between the groups. Dilute whole blood clot lysis time was increased in the diabetic group v controls (6.4 +/- 2.6 v 4.8 +/- 0.5 hours, respectively, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Systemic and transcardiac platelet activity in acute myocardial infarction in man: resistance to prostacyclin

There is increasing evidence that platelets play an important role in the pathogenesis of acute ischemic heart disease. Therefore an understanding of factors that influence platelet performance is important. This study was undertaken (1) to characterize during evolving myocardial infarction platelet activity in the peripheral circulation and across the ischemic/infarcting myocardial compartment, the locus of presumed platelet hyperactivity, and (2) to evaluate the effects of prostacyclin (PGI2), a most potent antiplatelet agent and vasodilator. A total of 59 patients with evolving myocardial infarction were studied. Twenty-two patients were instrumented with arterial and coronary sinus catheters and received intravenous infusion of PGI2, 13 +/- 4.5 ng/kg/min (mean +/- SD), for 90 min. In 15 patients with anterior myocardial infarction, transcardiac platelet function and response to PGI2 were studied. Plasma levels of beta-thromboglobulin (beta-TG) and of thromboxane B2 (TxB2), in vivo measures of platelet activity, were elevated three- and 10-fold. 6-Keto-prostaglandin F 1 alpha, the stable end product of PGI2, was less than 10 pg/ml, reflecting a leftward shift of the TxB2/PGI2 ratio. Platelets circulating during evolving myocardial infarction ("ischemic platelets") were hyperaggregable in response to ADP and relatively resistant to PGI2, both in vivo and in vitro. Concentrations of platelet cyclic AMP and the cyclic AMP response to PGI2 were diminished. The platelet hyperreactivity, expressed by plasma beta-TG, platelet aggregation, and PGI2-induced inhibition of aggregation, was most intense early during infarct evolution and decreased with time. The increased platelet performance resulted in "platelet fatigue," indicated by decreased contents of beta-TG of the ischemic platelet and decreased TxA2 production in response to collagen. However, the ischemic platelet produced twice normal TxA2 in response to arachidonic acid (stimulus and substrate), demonstrating a heightened metabolic capacity. TxA2 was produced across the ischemic/infarcting compartment in 10 of 15 patients with anterior myocardial infarction. The antiplatelet effect of PGI2 was greatly diminished. In summary, the data define an abnormal pattern of platelet behavior during evolving myocardial infarction, characterized by a proaggregatory environment, heightened platelet reactivity in both the peripheral and coronary circulation, and relative resistance to PGI2. The clinical consequences of the data are that the patient in the acute phase of myocardial infarction may benefit from suppression of platelet function and requires significantly greater doses of PGI2 than normal subjects.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evaluation of thromboxane production and complement activation during myocardial ischemia in patients with angina pectoris

BACKGROUND. The complement system and arachidonic acid metabolites are involved in severe myocardial ischemia such as myocardial infarction. Furthermore, there is experimental evidence for C5a participation in thromboxane production. METHODS AND RESULTS. We examined whether C5a and thromboxane are produced during brief and reversible episodes of myocardial ischemia induced in patients with stable angina. Twenty-five patients underwent either atrial pacing or percutaneous transluminal coronary angioplasty associated with arterial and coronary sinus blood sampling. Rapid atrial stimulation of patients with effort angina caused significant ST segment depression (delta ST = -1.7 +/- 0.2 mm), decreased fractional lactate extraction (from +12.8 +/- 2.5% baseline to -13.7 +/- 4.6% at peak ischemia, n = 13, p less than 0.001), and increased coronary sinus plasma thromboxane B2 levels (from 345 +/- 85 pg/ml baseline to 1,684 +/- 64 pg/ml at peak ischemia, p less than 0.01). Changes of fractional lactate extraction correlated significantly with changes of coronary sinus plasma levels of thromboxane B2. There was no change of coronary sinus 6-keto-PGF1 alpha levels. Similar pacing of control subjects (n = 6) did not cause release of lactate or thromboxane. Seventeen other patients underwent exercise testing with noninvasive measurements of thromboxane and prostacyclin metabolites in urinary samples collected before and after the test. No detectable increase of urinary 11-dehydrothromboxane B2 was measured in patients with stable angina after exercise-induced myocardial ischemia. However, basal 11-dehydrothromboxane B2 levels were significantly higher in patients with angina (105 +/- 25 pg/mmol creatinine, n = 9) than in control patients (45 +/- 8 pg/mmol creatinine, n = 8, p less than 0.05 between groups). Coronary sinus plasma levels of the anaphylatoxin C5a always remained below 4 ng/ml in patients undergoing pacing. More severe myocardial ischemia after coronary angioplasty (percent lactate extraction decreased from +24.8 +/- 2.7% baseline to -41.6 +/- 22.4% at peak ischemia, p less than 0.05) was not associated with C3a or C5b-9 generation. In all patients, there was neither platelet sequestration nor platelet alpha-granule release (no changes of beta-thromboglobulin/platelet factor 4 levels) into the coronary sinus plasma. CONCLUSIONS. Patients with stable angina have chronically increased thromboxane synthesis as assessed by excretion of urinary metabolites. Thromboxane is acutely released into the coronary sinus during pacing-induced ischemia without significant intracoronary platelet aggregation. Complement does not appear to be activated in stable angina during brief and reversible episodes of myocardial ischemia and does not contribute to thromboxane production.     

Effect of nafazatrom on platelet function and release: relationship to symptomatic episodes in patients with peripheral vascular disease

We studied the effect of nafazatrom on plasma prostacyclin (PGI2) levels, platelet function, and thromboxane B2 (TxB2), and 12-hydroxy-eicosatetraenoic acid (12-HETE) production and clinical improvement in 12 patients with peripheral vascular disease (PVD) by means of a double-blind crossover trial of placebo, 800 or 1600 mg of nafazatrom four times daily for 1 week, with intervening 2-week washout periods. Plasma PGI2 levels were measured as 6-keto-PGF1 alpha by radioimmunoassay. Platelet function ex vivo was measured as collagen and adenosine diphosphate (ADP)-induced platelet aggregation, release of 12-HETE and thromboxane A2 (measured as TxB2), and was determined by high-pressure liquid chromatography (HPLC) and radioimmunoassay, respectively. The plasma 6-keto-PGF1 alpha levels were unaffected by nafazatrom treatment (p greater than 0.25). Nafazatrom treatment had no effect on TxB2 production, but significantly altered the production of the platelet 12-HETE (p less than 0.05). There was a significant association between the changes in 12-HETE production and clinical improvement. These results suggest that the mechanism of action of nafazatrom is in part related to the inhibition of platelet function via the lipoxygenase pathway, independent of PGI2 stimulation.     

Effects of triflusal and acetylsalicylic acid on platelet aggregation in whole blood of diabetic patients

A study was made on the inhibitory effect of triflusal (600 mg/d X 15) and acetylsalicylic acid (ASA, 400 mg/d X 15) on platelet aggregation in whole blood (WB) and platelet-rich plasma (PRP) induced by ADP (2.5 mumol/l), adrenaline (50 mumol/l), collagen (1 microgram/ml) and arachidonic acid (0.8 mmol/l), in 30 insulin-dependent diabetic patients without vascular complications. Determination was also made of the serum levels of thromboxane B2 (TxB2) and of the plasma levels of 6-keto-PGF1-alpha and of beta-thromboglobulin (B-TG). Both drugs exhibited higher inhibitory effects in WB than in PRP. In WB, a significant difference between triflusal and ASA was observed against ADP-induced aggregation (67% and 46% inhibition respectively, p less than 0.01). Both drugs strongly inhibit the formation of TxB2 in serum (85% and 99%, respectively). Triflusal does not significantly change the plasma levels of 6-keto-PGF1-alpha; ASA, by contrast, causes reduction of over 95% in those plasma levels. The plasma levels of B-TG were not modified by either of the drugs.