Velocity Of Platelet Aggregation Research Articles

The disorders of blood oxygen transport function, hemostasis indicators and endothelium functional state in patients with ruptured arterial aneurysms and the development of delayed cerebral ischemia

Introduction. Rupture of cerebral aneurysms (CA) with the development of intracranial hemorrhage (ICH), complicated in some cases by vascular spasm and delayed cerebral ischemia (DCI), is due to the complex multifactorial genesis of the disease, including changes in the blood oxygen transport function (BOTF), activation of endothelial cells with a release of vasoregulators, reactive oxygen species, inflammatory proteins, as well as disturbances in the hemostasis system.Purpose – to study the indicators of BOTF, primary and secondary hemostasis and the content of some vasoregulatory metabolites in the pre- and postoperative periods in patients with ruptured CA with the development of DCI and without DCI.Materials and methods. The group with DCI included 45 patients; in the group without DCI were 14 people. Clinical-neurological and neuroimaging examinations were carried out, and parameters of BOTF, primary and secondary hemostasis, nitrate/nitrite, angiotensin-converting enzyme (ACE), and PAI-1 concentrations in venous blood were studied before and on days 10–12 after microsurgical clipping of the CA.Results. We diagnosed mild neurological disorders according to the NIHSS scale, confirmed by neuroimaging studies of the brain in the group of DCI patients. It was shown an increase in thrombin-dependent platelet aggregation velocity to 30.6 (24.3; 32.4) AU/min at norm 21.8 (20.3; 24.9) (U, p=0.009) before surgery; and after surgery it was up to 37.4 (30; 44.7) relative to the norm (U, p=0.001). Before surgery, the following was observed: PT shortening to 11.6±0.7 sec at norm 13.2±1.1 (t, p˂0.001), fibrinogen concentration increasing to 4.35 (3.8; 4.8) g/L at norm 3.9 (3.6; 4.1) g/L (U, p = 0.01) and PAI-1 up to 3.9 (2.6; 4.8) ng / mL at norm 2 .7 (2.2; 4.1). After surgery, PT was 11.9±1.1 (t, p˂0.001); fibrinogen - 4.4 (3.9; 4.8) (U, p=0.024), PAI-1 - 4.6 (4.1; 6.7) (U, p=0.0004) respectively. Before surgery, p50 was increased to 28.1 (26.2; 31.6) mm Hg at norm 25.2 (24.3; 26.8) (U, p=0.025); after surgery, it was up to 28.5 (26.8; 30.7) (U, p=0.03) and the ratio of nitrates/nitrites to ACE was reduced to 0.12 (0.08; 0.15) at norm 0.22 (0.15; 0.32) (U, p˂0.001); after - up to 0.11 (0.08; 0.19) (U, p˂0.001) respectively.Conclusion. There has been revealed significant disorders of primary and secondary hemostasis with fibrinolysis inhibition, a decrease in the affinity of hemoglobin to oxygen at the p50 rate and an imbalance of the content of vasoregulatory metabolites in patients with DCI before and after aneurysm clipping, which can be considered as significant factors in the development of DCI after aneurysmal ICH.

Does platelet aggregation have any importance in fetal growth restriction pregnancies?

The aim of the study was to evaluate platelet (PLT) concentration, mean platelet volume (MPV), PLT aggregation and its velocity in pregnancy complicated with fetal growth restriction (FGR) and to analyze the PLT aggregation according to the gestational age and Doppler velocimetry. The study group included 29 pregnant women diagnosed with FGR. The control group-consisted of 27 females in uncomplicated pregnancy. Then both groups were divided according to the gestational week (< and ≥ 36 weeks) and Doppler velocimetry results. The adenosine diphosphate (ADP) induced PLT aggregation was performed with the help of the electrical impedance. There was a significant positive correlation between gestational age and PLT aggregation and between gestational age and velocity of PLT aggregation in FGR. Patients with FGR ≥ 36 weeks of gestation had 73% higher PLT aggregation than control group. Within the FGR group, the PLT aggregation was 135% higher in pregnancies ≥ 36 weeks as compared to < 36 weeks of gestation. In FGR pregnancies ≥ 36 weeks with impaired flow in both uterine arteries (UtA), 2.3-fold higher PLT aggregation was found as compared to FGR patients with normal flow or abnormal flow in one UtA. The increased PLT aggregation in FGR is related to gestational week and occurs in pregnancies ≥ 36 weeks of gestation. The PLT hyperaggregability in growth-restricted pregnancies is associated with abnormal Doppler velocimetry in both UtA, comparing to patients with altered blood flow in one UtA or normal pulsatility index in both UtA, suggesting the PLT activation due to impaired uteroplacental circulation.

An Intergenic Noncoding Chromosome 18 Variant Suppresses Lethal Thrombosis in Mice By Normalizing Blood Coagulation and Reducing Platelet Reactivity

Background: Factor V Leiden (FVL) is a common thrombosis susceptibility variant in humans. It is incompletely penetrant; this indicates that there are modifiers of FVL that alter thrombosis susceptibility. We used mouse models of FVL (F5L) and heterozygous tissue factor pathway inhibitor deficiency (Tfpi+/-), to identify a perinatal lethal genetic interaction when mice inherited F5L/L Tfpi+/-. This phenotype was used as the basis for a sensitized genome wide ENU mutagenesis screen to identify mutations suppressing lethal thrombosis in F5L/L Tfpi+/- mice. From this screen, we generated multiple independent lines of thrombosuppressed mice, called MF5L, for Modifier of F5L. MF5L16 was a large, highly penetrant (77.2%), multigenerational pedigree containing 136 viable F5L/L Tfpi+/- mice.Aims: In the present study, we aimed to identify and functionally characterize the thrombosuppressor mutation present in MF5L16.Methods: Genomic analyses: We performed whole genome sequencing (WGS) on four MF5L16 F5L/L Tfpi+/- mice. We used comparative bioinformatic analyses to identify variants inherited by all four mice and compiled these variants into candidate variant list. PCR and Sanger sequencing were used to analyze the 136 F5L/L Tfpi+/- mice for inheritance of each of the candidate variants. Functional analyses: We performed biochemical blood coagulation and platelet assays of blood from the Chr18 A mice . Complete blood counts were measured using the Advia 2120 with settings optimized for C57BL/6 mouse blood. Platelet aggregation studies were performed using the Roche Multiplate Aggregometer with ADP and type 1 collagen as the aggregating agents.Results: We analyzed four MF5L16 mice by WGS and identified seven spontaneous mutations that arose in our F5L/L breeding colony that were introduced into MF5L16. Importantly, no coding variants were linked to these variants. Analysis of these seven mutations in all 136 MF5L16 F5L/L Tfpi+/- mice revealed a significant association between a Chromosome 18 intergenic variant (Chr18 G to A, Chr18 A) and F5L/L Tfpi+/- mouse survival (p=0.003). To re-create the suppression of the lethal F5L/L Tfpi+/- phenotype, we bred F5+/L Tfpi+/- Chr18 +/A triple heterozygous mice to F5L/L Chr18 A/A mice to observe the effects of Chr18 A on F5L/L Tfpi+/- mouse survival. Out of 109 mice from this cross, two F5L/L Tfpi+/- Chr18 +/A mice were produced (expected ratio ~1:8). This suggests that the Chr18 A variant suppresses F5L/L Tfpi+/- lethal thrombosis at ~15% penetrance. Complete blood count analysis on Chr18 +/+,Chr18 +/A, and Chr18 A/A mice determined that Chr18 A/A mice had reduced platelet count and distribution width and increased variability in red blood cell (RBC) mean corpuscular volume (n≥4; p<0.05). The Chr18 A/A mice did not display differences in PT or aPTT assays, but had significantly reduced platelet aggregation velocity when stimulated by both ADP and collagen agonists (n≥4; p=0.0002). Additionally, blood smears revealed the presence of poikilocytic RBCs in the Chr18 A/A mice.Conclusions and future directions: Our results establish that a noncoding intergenic Chr18 variant at nucleotide position 62,970,011 (G>A, Chr18 A) contributes to thrombosuppression by reducing platelet reactivity. The observed platelet and RBC phenotypes suggest that a major mechanism of Chr18 A thrombosuppression could be through regulation of gene expression in cells of the myeloid lineage. We are performing additional platelet and blood coagulation analyses to refine the phenotypic differences due to the Chr18 A variant. Comparative transcriptomic analyses are also being performed to identify the genetic pathways involved. Understanding the mechanism in which this intergenic mutation suppresses thrombosis could provide insights into human thrombosis regulation. DisclosuresNo relevant conflicts of interest to declare.

Pleiotropic Activity of Metformin and Its Sulfonamide Derivatives on Vascular and Platelet Haemostasis.

As type 2 diabetes mellitus (T2DM) predisposes patients to endothelial cell injury and dysfunction, improvement of vascular function should be an important target for therapy. The aim of this study was to evaluate the effects of metformin, its sulfenamide and sulfonamide derivatives on selected parameters of endothelial and smooth muscle cell function, and platelet activity. Metformin was not found to significantly affect the viability of human umbilical vein endothelial cells (HUVECs) or aortal smooth muscle cells (AoSMC); however, it decreased cell migration by approximately 21.8% in wound healing assays after 24 h stimulation (wound closure 32.5 µm versus 41.5 µm for control). Metformin reduced platelet aggregation manifested by 19.0% decrease in maximum of aggregation (Amax), and 20% reduction in initial platelet aggregation velocity (v0). Furthermore, metformin decreased spontaneous platelet adhesion by 27.7% and ADP-induced adhesion to fibrinogen by 29.6% in comparison to control. Metformin sulfenamide with an n-butyl alkyl chain (compound 1) appeared to exert the most unfavourable effects on AoSMC cell viability (IC50 = 0.902 ± 0.015 μmol/mL), while 4-nitrobenzenesulfonamide (compound 3) and 2-nitrobenzenesulfonamide (compound 4) derivatives of metformin did not affect AoSMC and HUVEC viability at concentrations up to 2.0 μmol/mL. These compounds were also found to significantly reduce migration of smooth muscle cells by approximately 81.0%. Furthermore, sulfonamides 3 and 4 decreased the initial velocity of platelet aggregation by 11.8% and 20.6%, respectively, and ADP-induced platelet adhesion to fibrinogen by 76.3% and 65.6%. Metformin and its p- and o-nitro-benzenesulfonamide derivatives 3, 4 appear to exert beneficial effects on some parameters of vascular and platelet haemostasis.

Wild-type isolates of Porphyromonas gingivalis derived from periodontitis patients display major variability in platelet activation.

Extent and velocity of platelet aggregation were determined by light transmission aggregometry. Platelet surface expression of P-selectin was measured by flow cytometry, activation of p38 MAP kinase, and protein kinase C by Western blot using phospho-specific antibodies. Pg isolates displayed high variability regarding extent and velocity of platelet activation, as well as the involved activating pathways. Corresponding results were observed for platelet P-selectin expression, activation of p38 MAP kinase, or protein kinase C. Inhibitors of platelet immune receptor FcγRIIA and protease-activated receptors revealed several, diverging pathways of activation. Some isolates induced platelet aggregation even in the presence of potent therapeutical platelet inhibitors. Chronic bacteremia involving specific, platelet-activating Pg strains may constitute a substantial hazard for the integrity of cardiovascular health.

Different training schedules influence platelet aggregation in show jumping horses.

Depending on the intensity, duration and type of physical exercise, equine metabolism has to adapt to nervous, cardiovascular, endocrine and respiratory system requirements. In horses, exercise and training are known to have considerable effects on the mechanisms of hemostatic system involving platelet activity. The aim of the present study was to evaluate the effect of different training schedules on platelet aggregation in 15 Italian Saddle jumping horses. Animals were divided into three equal groups: Group A was subjected to a high intensity-training program; group B to a light training program, group C included sedentary horses. From each animal, blood samples were collected by jugular venipuncture at rest on the 1st, 3rd and 5th days, and afterwards, once a week, for a total of 5 weeks data recording, in order to assess the maximum degree of platelet aggregation and the initial velocity of aggregation (slope) platelet aggregation. Two-way analysis of variance (ANOVA) showed a significant effect of the different training schedules on studied parameters. The results revealed a different degree of platelet aggregation and a different initial velocity of platelet aggregation that changes during the different training schedules in horses that could represent a different protective endothelial mechanism. These findings could have an important role for a clearer knowledge of the physiological reference values of platelet aggregation and for a better interpretation of these variations during the training.

ADP-induced platelet aggregation after addition of tramadol in vitro in fed and fasted horses plasma

Adenosine diphosphate (ADP)-induced platelet aggregation in fed and fasted horses after addition of tramadol hydrochloride was evaluated in vitro. On 10 horses citrated blood samples were collected 2h after feeding (fed animals) and 21h after feeding (fasted animals). Final concentrations of ADP 1 and 0.5μM, and tramadol hydrochloride (1, 15, 30, 45 and 60min after the addition of tramadol) were used to determine the maximum degree and initial velocity of platelet aggregation. Repeated measures multifactor analysis of variance (MANOVA) was used to evaluate the effect of feeding/fasting condition, ADP concentration and addition of tramadol. Findings showed statistical differences (P⩽0.05) on studied parameters after addition of tramadol to different ADP concentrations in fed and fasted horses. The clinical relevance of these results is that tramadol provides many advantages as a therapeutic option; in fact, it is an inexpensive and a relatively new analgesic in equine veterinary medicine. Further investigations would be appropriate to compare the effects of different opioids but also using different concentrations of tramadol associated with other drugs in order to have substances which can regulate the functional activity of the platelets and to extend the knowledges on equine platelet aggregation.

Abstract 215: Inflammation-Induced Thrombogenic Phenotype in the Microvasculature: The Roles of Enhanced Platelet Production and Reactivity

It is well recognized that different pathological conditions associated with inflammation are also accompanied by altered platelet function and enhanced thrombus development. Experimental colitis (induced by dextran sodium sulfate, DSS) and angiotensin II (AngII)-induced hypertension (HTN) are two examples of pathologically distinct inflammation models that exhibit enhanced platelet adhesion in venules and accelerated thrombus formation in arterioles. Whether these responses represent alterations in platelet production, life-span, and/or function remains unclear. In this study, we compared the changes in platelet production and reactivity (to thrombin) that occur in murine models of DSS colitis and AngII-induced HTN. Mature (TO-) and immature (TO+) platelets in blood were quantified using thiazole orange (TO) staining with flow-cytometry. The in vivo biotinylation method was used to determine the life-spans of TO+ and TO- platelets. Platelet aggregation velocity was measured using a low-angle light scattering technique. Thrombus formation, induced by light/dye injury, was monitored in cremaster muscle arterioles and platelet adhesion was quantified in the venules. Our findings indicate that both models of inflammation promote platelet adhesion and enhanced thrombus formation in the microvasculature. The enhanced thrombosis normally detected in both DSS-induced colitis and AngII-induced hypertension models was not evident in interleukin-6 (IL-6) deficient mice and in WT mice treated with an IL-6 receptor blocking antibody. DSS colitis was accompanied by an increased appearance of both TO+ and TO- platelets, increased platelet reactivity (aggregation) to thrombin, and no change in platelet turnover. The AngII HTN model exhibits an increase in platelet turnover, an increased number of TO- (but not TO+) platelets, and no change in platelet aggregation, suggesting that an altered endothelial cell phenotype likely makes a larger contribution to the accelerated arteriolar thrombosis in this model. The divergent responses in these two IL-6 dependent models of microvascular thrombosis may reflect the relative importance of platelets and microvascular endothelial cells as molecular targets for IL-6 mediated thrombogenic responses.

Effect of Different Storage Conditions on Platelet Aggregation in Horse

Platelet aggregation is the most important event in the hemostatic process, but no information is available on the stability of samples for aggregation testing in horses. The aim of the present study was to evaluate the effect of different storage conditions on platelet aggregation in horses. The study was carried out on 58 healthy horses of varying breed and gender, ranging in age from 4 to 12 years. Citrated blood samples were collected from all the subjects by means of jugular venipuncture and were used for platelet aggregation measurements. Platelet-rich and platelet-poor plasma samples were prepared by centrifugation and divided into six different aliquots to assess the maximum degree of platelet aggregation and the initial velocity of platelet aggregation at the final concentrations of 1 and 0.5 μM of the aggregating agent. The first aliquot was analyzed within 1 hour after collection at room temperature (22°C), the second 6 hours after collection at 22°C, the third and fourth were refrigerated at 8°C for 6 and 24 hours, respectively, and the fifth and sixth were frozen at −20°C for 24 and 48 hours, respectively. With the help of an aggregometer, platelet responses were quantified, and one-way repeated measures analysis of variance was used to determine significant differences. Probability values of <.05 were considered to be statistically significant. Analysis of variance showed statistically significant differences on maximum degree of platelet aggregation and the initial velocity of platelet aggregation using adenosine diphosphate at final concentrations of 1 and 0.5 μM. The results of this study suggest that the storage of equine plasma for more than 6 hours at room temperature and at 8°C has a significant effect on platelet aggregation, and that the storage of plasma for 24 and 48 hours at −20°C alters platelet aggregation. In conclusion, storage conditions had a statistically significant effect on the parameters of platelet aggregation directly correlated to temperature.

Hydrocortisone inhibition of adenosine diphosphate (ADP)-induced platelet aggregation in horse

The aim of this study was to evaluate the effect of hydrocortisone on adenosine diphosphate (ADP)-induced platelet aggregation in horse. The study was carried out on 35 healthy horses of various breeds and gender. On all horses, citrated blood samples were collected by jugular venipuncture to assess platelet aggregation. On all samples, platelet-rich and platelet-poor plasma were prepared by centrifugation and divided into two different aliquots. On the first aliquot, platelet aggregation was determined after platelet activating with 1 and 0.5 μM ADP (group A). On the last one, the effect of 20-min preincubation with hydrocortisone in ADP-induced aggregation was determined at final ADP concentrations of 1 and 0.5 μM (group B). By means of an aggregometer, the platelet response was quantitated as maximum degree of platelet aggregation and initial velocity of platelet aggregation. All data were analyzed using unpaired Student's t test. A P ≤ 0.05 was considered statistically significant. The obtained results showed a statistically significant effect of hydrocortisone on both the maximum degree of platelet aggregation and the slope of platelet aggregation at the two final concentrations of ADP used. These results are compatible with the possibility that the vessel wall releases smooth muscle-relaxing prostaglandins when injured and that the inhibition of prostaglandin formation by hydrocortisone enhances hemostasis by allowing vasoconstriction to be maintained. Further investigations could be useful utilizing different concentrations of hydrocortisone in order to apply the knowledge of the effect of glucocorticoids on platelet aggregation.

Étude des effets directs et indirects de l’érythropoïétine dans un modèle expérimental de thrombose et de saignement chez le lapin

Objectives. – To study direct and indirect effects of EPO on haemostasis. Study design. – Experimental, randomised. Animals. – Forty-eight New Zealand rabbits. Method. – Animals were anaesthetised, ventilated and monitored continuously for blood pressure, heart rate, body temperature, and carotid blood flow variations and were randomised into four groups: control, EPO bolus 2400 IU kg –1, fractionated EPO (one injection a week of 600 IU kg –1 for 4 weeks), homologous red blood cell transfusion to reach the Ht level of the fractionated EPO group. A compression injury and a 75% stenosis of the carotid artery triggered a series of cyclic flow reductions (CFRs). CFRs were observed for a 20 min period in each group. Ear immersion bleeding time (BT) and hepato-splenic bleeding were performed at the end of the experiment. Biology was performed at the end of the thrombosis period: blood cells count, Hte, activated partial thromboplastin time, fibrinogen, arachidonic-induced platelet aggregation, EPO dosages. Results. – No significant increase in thrombosis (CFRs) in the two EPO groups and in the transfused group. Increase in Hte in the fractionated EPO group versus control. Group EPO bolus: decrease in BT and hepato-splenic bleeding versus control; decrease in hepato-splenic bleeding versus fractionated EPO group, increase in platelet aggregation velocity versus control. Conclusion. – EPO did not increase the thrombotic risk in this rabbit model. EPO bolus decreased BT and hepato-splenic bleeding.

Influence of the genetic background on platelet function, microparticle and thrombin generation in the common laboratory mouse

Genetic background has been shown to affect phenotype in transgenic mice with hemostatic defects. We present comparative data on various platelet function tests, as well as on microparticle and thrombin generation capacity in three mouse strains most commonly used in transgenic applications. Normal, inbred 129Sv ( n = 24), C57BL/6 ( n = 14) and BALB/c ( n = 22) mice were used. BALB/c mice showed statistically significantly longer tail-bleeding times (158 - 42 s, P <0.02) than 129Sv (113 - 37) and C57BL/6 (122 - 29) and paradoxically increased velocity of platelet aggregation ( P <0.01) with ADP, collagen, ionophore and thrombin. ATP-release did not differ between strains, it was weakest with ADP and strongest with thrombin. 129Sv platelets were less responsive to thrombin. Generation of platelet microparticles did not differ between strains either and could efficiently be inhibited by EDTA but not by aspirin or alprostadil. Two anti-GPIIIa monoclonal antibodies did not inhibit microparticles either, although they could block aggregation. Thrombin generation was equivalent in C57BL/6 and BALB/c, but slower in 129Sv. Interestingly, the reaction in all strains was immediate and different from the human model in that no lag-phase was seen after triggering. In summary these mouse strains show similar patterns of ex vivo platelet aggregation, bleeding times as well as microparticle and thrombin generation. Subtle differences were found, which should be taken into consideration when interpreting data from wild-type or transgenic models.

A vitamin E concentrate rich in tocotrienols had no effect on serum lipids, lipoproteins, or platelet function in men with mildly elevated serum lipid concentrations

Tocotrienols, lipid-soluble antioxidants with vitamin E activity, have been reported to lower LDL-cholesterol concentrations and platelet aggregation in men, but results are contradictory. To examine in detail the effects of a vitamin E concentrate rich in tocotrienols on serum lipoproteins and on platelet function in men at risk for cardiovascular disease. In this randomized, double-blind, placebo-controlled parallel trial, 20 men received daily for 6 wk 4 capsules, each containing 35 mg tocotrienols and 20 mg alpha-tocopherol; 20 other men received 4 capsules daily, each providing 20 mg alpha-tocopherol. All men had concentrations of serum total cholesterol between 6.5 and 8.0 mmol/L or lipoprotein(a) concentrations > 150 mg/L. Compliance was confirmed by changes in serum tocopherol and tocotrienol concentrations. Serum LDL cholesterol in the tocotrienol group was 4.80 mmol/L before and 4.79 mmol/L after intervention, and increased from 4.70 to 4.86 mmol/L in the placebo group (95% CI for the difference: -0.54, 0.19 mmol/L; P = 0.333). Also, changes in HDL cholesterol, triacylglycerol, lipoprotein(a), and lipid peroxide concentrations did not differ between the groups. After adjustment for differences in initial values, no effects were found on collagen-induced platelet aggregation velocity, maximum aggregation, or thromboxane B2 formation in citrated whole blood. ATP release, however, was lower in the tocotrienol group. Urinary thromboxane B2 and 11-keto-thromboxane B2 concentrations and coagulation and fibrinolytic measures did not change. The tocotrienol supplements used had no marked favorable effects on the serum lipoprotein profile or on platelet function in men with slightly elevated lipid concentrations.

Platelet aggregation in atopic dermatitis

Many observations suggest the active role of platelets in allergic inflammation. However, this problem is poorly researched in atopic dermatitis. The aim of study was to examine the intensity and velocity of platelet aggregation and a potential relationship with some immunological parameters (total IgE and specific-IgE serum levels) in atopic dermatitis patients. Platelet aggregation was evaluated in 12 subjects with atopic dermatitis and 12 healthy, nonatopic persons, according to the Born method, in a dual-channel aggregometer, in response to three exogenous stimulators (ADP, thrombin and collagen). The intensity and velocity of platelet aggregation and total platelet counts did not differ between the two groups irrespective of the type of extrinsic stimulator used. In contrast to other atopic diseases, in atopic dermatitis platelet aggregation is not impaired.

Evaluation of Platelet Function by Kinetic Analysis of Platelet Aggregation

Platelet aggregation is usually measured by a spectroscopic method using an aggregometer. However, when the process of platelet aggregation is followed by the changes in light transmission of platelet-rich plasma (PRP), factors such as platelet deformation or changes in plasma permeability must be taken into consideration. Thus, a better method was developed in our laboratory for measuring platelet aggregation by chronologically counting non-aggregated single platelets, one of the simplest parameters of the aggregation process, using PRP to which adenosine diphosphate (ADP) was added.(1,2) In the present study, we attempted to further evaluate platelet aggregability by measuring the velocity of platelet aggregation in different subjects using our single platelet counting method.

Effect of Fibrinogen Concentration on the Velocity of Platelet Aggregation

Abstract The relationship between fibrinogen binding to its receptor and platelet aggregation has been investigated by comparing 125I-fibrinogen binding and aggregation velocities of gel-filtered platelets in the presence of adenosine diphosphate (ADP). Aggregometric responses at various fibrinogen concentrations are found to be bell-shaped and show a maximum at fibrinogen concentrations (Fmax) similar to the 125I- fibrinogen hemisaturating doses. At higher and lower fibrinogen concentrations, platelet aggregation velocities decrease in a parallel manner. Lowering ADP concentration increases Fmax, in agreement with the modulatory effect of ADP on fibrinogen binding to platelets. Variations of fibrinogen in the range of physiopathologic plasma concentrations affect platelet aggregation induced by any ADP dose. These results clarify the relationship between the fibrinogen binding process and aggregation and demonstrate that plasma fibrinogen concentration has a major influence on the velocity of platelet aggregation.

Effect of fibrinogen concentration on the velocity of platelet aggregation

The relationship between fibrinogen binding to its receptor and platelet aggregation has been investigated by comparing 125I-fibrinogen binding and aggregation velocities of gel-filtered platelets in the presence of adenosine diphosphate (ADP). Aggregometric responses at various fibrinogen concentrations are found to be bell-shaped and show a maximum at fibrinogen concentrations (Fmax) similar to the 125I-fibrinogen hemisaturating doses. At higher and lower fibrinogen concentrations, platelet aggregation velocities decrease in a parallel manner. Lowering ADP concentration increases Fmax, in agreement with the modulatory effect of ADP on fibrinogen binding to platelets. Variations of fibrinogen in the range of physiopathologic plasma concentrations affect platelet aggregation induced by any ADP dose. These results clarify the relationship between the fibrinogen binding process and aggregation and demonstrate that plasma fibrinogen concentration has a major influence on the velocity of platelet aggregation.

Effect of fibrinogen concentration on the velocity of platelet aggregation

Effect of fibrinogen concentration on the velocity of platelet aggregation

The effect of carbonic anhydrase inhibition on the velocity of thrombin-stimulated platelet aggregation under physiological conditions

We have studied the effect of ethoxzolamide, a specific carbonic anhydrase inhibitor, on the velocity of thrombin-stimulated platelet aggregation. After preincubation of platelet rich plasma with 10 −6 M ethoxzolamide the velocity of platelet aggregation was reduced by about 40%. Between 10 −11 M and 10 −10M ethoxzolamide was necessary to achieve a half-maximal diminution of the aggregation velocity. An identical maximal reduction of the velocity of aggregation as with ethoxzolamide could be achieved by a nearly complete removal of CO 2 from the platelet rich plasma. These results suggest that the intracellular CO 2 hydration-dehydration reaction is involved in the activation of human platelets by thrombin. It is possible that the cytosolic carbonic anhydrase of platelets provides a rapid source of the protons that are transferred across the plasma membrane during the activation process.

Fibrinogen binding and ADP-induced aggregation in platelets from diabetic subjects.

Abstract The factors responsible for the platelet hyperaggregability often found in diabetics are obscure. Since fibrinogen is essential for ADP-induced aggregation and specific fibrinogen receptors exist on the platelet membrane, ADP-induced platelet aggregation and fibrinogen binding were measured in 16 diabetics (8 background and 7 proliferative retinopathy, 1 maculopathy) and 9 non-diabetic controls. The velocity of platelet aggregation induced by a range of concentrations of ADP was measured and the 1/Km (1/μM ADP) derived from a Lineweaver-Burk plot. 125I-fibrinogen binding was measured in washed platelets and expressed as per cent total radioactivity. Metabolic control of diabetes was assessed by HbA1. Mean per cent specific fibrinogen binding 15 min after the addition of ADP was significantly increased in the 8 diabetics with severe retinopathy compared to controls (5.08 ± 1.04 SEM vs 3.04 ± 0.53: p