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PubMed1996

Thrombospondin peptides inhibit the secretion-dependent phase of platelet aggregation.

Thrombospondin (TSP) is a platelet alpha-granule adhesive glycoprotein (M(r) = 450,000) that is released in large amounts from activated platelets and participates in thrombus formation. The aim of the present study was to assess the effect of peptides corresponding to sequences within the NH2-terminal region and type 1 repeats of TSP on platelet aggregation induced by thrombin in washed platelet suspensions. We found that TSP18 (amino acids 1-174), used at micromolar concentrations, inhibited platelet aggregation by 30-50%, reducing the size of the aggregates formed. Similar results were obtained with the hexapeptide Cys-Ser-Val-Thr-Cys-Gly (amino acids 429-434 and 486-491) used at 1.2 mM. The shorter peptide Val-Thr-Cys-Gly was even more inhibitory whereas the peptide Val-Thr-Lys-Gly, which lacks a cysteine, had no effect. Interestingly, we have constantly found that inhibition of platelet aggregation by these peptides was accompanied by an inhibition of alpha and dense granule secretion, suggesting that the binding of secreted TSP to the plasma membrane may participate in the platelet signaling process. We conclude that peptides of TSP may prove useful in the treatment of thrombosis by impairing both the release of proaggregating substances and platelet macroaggregate formation.

Blood Platelets↗
PubMed1979

Platelet aggregation studies during transient hypoglycaemia: a potential method for evaluating platelet function.

The effect of acute hypoglycaemia on platelet function was examined in patients undergoing an insulin stress test. Enhanced platelet aggregation was observed in all cases but platelet count, platelet adenine nucleotides, and the plasma level of von Willebrand factor were unchanged overall. The onset of the hypoglycaemia-induced increase in platelet aggregation coincided with the lowest blood glucose levels recorded and with the clinical signs of adrenaline release. Increased platelet aggregation was maintained thereafter for the two-hour test period. There was no apparent correlation with changes in cortisol, growth hormone, and prolactin. No change in platelet function was observed after the administration of L-dopa. We suggest that the measurement of platelet aggregation during a standard insulin stress test may provide a means of evaluating platelet function in vivo and the influence of drugs thereon.

Adenine Nucleotides↗
PubMed1984

Effect of heparin on platelet aggregation.

The effect of heparin on platelet aggregation was systematically examined on platelets in plasma (PRP), as well as on gel-filtered, washed, and formaldehyde-fixed platelets. Results indicate that, although heparin causes a mild potentiation of platelet aggregation in the PRP systems, a significant inhibitory activity is observed when heparin is added to isolated platelets. This inhibitory activity appears to be specific and not related to the impurities in the heparin preparations, as heparinase, as well as protamine, effectively neutralizes the heparin-mediated inhibitory activity on platelet aggregation. Although heparin-mediated inhibitory activity can be demonstrated in the presence of a number of different agonists (ADP, arachidonic acid, thrombin, Ionophore A23187, epinephrine, and ristocetin), the most pronounced inhibition is seen in the presence of ristocetin. Further studies show that heparin enhances thromboxane generation in isolated platelets. Platelets pretreated with heparin, however, fail to respond to preformed thromboxane. These findings suggest that, in addition to the potentiation of thromboxane production in platelets, heparin may also attribute some change(s) to the platelet(s)/platelet membrane, which interferes with their ability to respond to the agonists of platelet aggregation. This antiaggregatory activity of heparin was found to be inhibited by a factor(s) present in plasma but not in serum.

Blood Coagulation↗
PubMed1997

Anger expression correlates with platelet aggregation.

Potential relationships between increased platelet aggregability and such psychological characteristics as hostility and anger were investigated as part of a larger intervention study investigating the potential efficacy of stress-reduction treatments. Participants performed 6-minute mental arithmetic tests under time pressure. Blood was sampled during the first minute of the task and whole blood platelet aggregation was measured in an aggregometer, using collagen and ADP. To assess anger and hostility, the authors used Spielberger's State-Trait Anger and Anger Expression scales together with the Cook-Medley Hostility Scale. The authors found positive correlations between collagen-induced platelet aggregation and outwardly expressed anger, as measured by the Anger Expression Scale. The findings suggested that modes of anger expression may be associated with increased platelet aggregation. If confirmed by future studies, this finding could provide a mechanism for the putative connection between anger/hostility and coronary heart disease.

Adolescent↗
PubMed1989

[Effects of anti-platelet aggregating agents on peplomycin induced pulmonary toxicity in mice].

In order to find a method to ameliorate pulmonary toxicity of peplomycin (PEP), microscopic changes of the lung following PEP administration and effect of anti-platelet aggregating agents on the toxicity was investigated in mice. When PEP was administered intravenously once a day for 7 days, microthrombi mainly composed of aggregated platelets and fibrin appeared in the capillaries of the lung in an early phase before severe pulmonary edematous lesions and fibrosis occurred. Combination therapy of anti-platelet aggregating agents such as phthalazinol, dipyridamole, ticlopidine and indomethacin suppressed these toxic changes. Especially, ticlopidine was the most effective and superior to prednisolone used clinically for amelioration of the toxicity. Microthrombi, preceding edematous lesions, were considered to be attributed to damages of endothelium by PEP, because PEP itself did not develop platelet aggregation in vitro and ex vivo. Therefore, the microthrombi are likely to produce congestion of pulmonary microcirculation leading to edematous lesions by increase of permeability, and to play significant roles in the development of pulmonary fibrosis in a late phase. Anti-platelet aggregating agents such as ticlopidine are concluded to ameliorate the lung toxicity by preventing microcirculation impairment with the microthrombus.

Animals↗
PubMed1986

Anesthetics and anticoagulants used in the preparation of rat platelet-rich-plasma alter rat platelet aggregation.

Aggregation of platelets in heparin- and citrate-anticoagulated platelet-rich-plasma (PRP) from rats anesthetized with methoxyflurane (M), diethyl ether (E), acepromazine/ketamine (A/K), or sodium pentobarbital (P) is described, as are platelet counts. Platelet counts were highest in heparin- or citrate-PRP from E and A/K anesthetized rats. Collagen and arachidonic acid (AA) induced aggregation in heparin-PRP only, and ADP induced greater aggregation in heparin-PRP than in citrate-PRP. Differences between citrate-PRP and heparin-PRP are probably due to citrate inhibition of platelet aggregation, since addition of citrate to heparin-PRP decreased aggregation, while addition of heparin to citrate-PRP did not alter aggregation. Aggregation of hirudin-PRP was slightly less than heparin-PRP. Anesthetics affected rat platelet aggregation: the rank order of the maximal extent of ADP-induced aggregation in citrate-PRP was M greater than E = A/K greater than P, and that for AA and collagen in heparin-PRP was E = A/K greater than M = P. The correlation between the effect of the anesthetics and activation of the sympathoadrenal system is discussed. It appeared that of the commonly used anticoagulants and anesthetics, heparin and methoxyflurane had the least influence on rat platelet aggregation.

Anesthetics↗
PubMed1991

Inhibition of human and rabbit platelet aggregation by chlorophenoxyacid herbicides.

Inhibition of human platelet aggregation by eight chlorophenoxyacid herbicides was studied in vitro. Thrombocyte aggregation in the platelet-rich plasma was induced by 1.0-32.0 microM adenosine diphosphate (ADP), 0.32-32.0 microM adrenaline or 7.5-30.0 micrograms/ml collagen with and without chlorophenoxyacid (0.05-2.0 mg/ml). Platelet aggregation by each inducer was inhibited dose dependently by all the eight chlorophenoxyacids at concentrations between 0.1 and 2.0 mg/ml. Increasing the concentrations of ADP and collagen but not of adrenaline inhibited the antiaggregatory action of chlorophenoxy-acids. No essential differences in inhibitory effect were found between different chlorophenoxyacids varying in respect of their ring substituents and the length of the carboxylic side chain. In the platelet-rich plasma prepared from rabbits 2.5 h after subcutaneous injection of 2.4-dichlorophenoxyacetic acid or 4-chloro-2-methylphenoxyacetic acid (100-150 mg/kg), platelet aggregation by ADP was inhibited 20-30%, compared to plasma taken from the rabbits before the chlorophenoxyacid treatment. The inhibition had disappeared by 20-23 h after administration. The results indicate that chlorophenoxyacid herbicides inhibit human platelet aggregation. Furthermore, the inhibition is probably involved in haemorrhages known to occur in various tissues of animals intoxicated by chlorophenoxyacid herbicides.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed1980

Inhibition of platelet aggregation and elevation of cyclic-AMP levels in platelets by 13,14-dehydro PGI2 methyl ester.

13,14-Dehydro PGI2 (dh-PGI2) and 13,14-dehydro PGI2 methyl ester (dh-PGI2-Me) inhibited platelet aggregation and release of [14C]-serotonin and ADP induced by collagen, ADP, arachidonic acid and PGG2. The inhibitory dose (ID50) ofg dh-PGI2-Me on platelet aggregation was 3 x 10(-9)M when induced with collagen, 2 x 10(-8) M with ADP, 5 x 10(-9) M with arachidonic acid and 1 x 10(-8)M with PGG2. The effects of dh-PGI2 and dh-POGI2-Me on platelet aggregation appear to be mediated by cyclic AMP, since both agents were potent to stimulate platelet cyclic AMP formation. In this respect dh-PGI2-Me was more effective than dh-PGI2 and PGE1. The actions of dh-PGI2-Me on platelet aggregation reported in this study suggest that is posseses similar biological properties as natural PGI2. Since dh-PGI2-Me is considerably more stable at physiological pH than PGI2 (Fried, J. and Barton, J. (1977) Proc. Natl. Acad. Sci. USA, 74, 2199-2203) this PGI2 analog might be useful as an anti-thrombotic drug.

Adenosine Diphosphate↗
PubMed1989

Whole blood platelet aggregation in uremic dogs.

Whole blood platelet aggregation responses to collagen, arachidonic acid, and adenosine diphosphate were determined by use of the impedance method in 22 dogs with serum urea concentrations greater than or equal to 20 mmol/L, which was attributable to renal disease, and in 25 healthy control dogs. The median changes in impedance for the control dogs were 23 ohms for collagen, 18 ohms for arachidonic acid, and 6 ohms for adenosine diphosphate. The median changes in impedance in uremic dogs were 25 ohms for collagen, 21 ohms for arachidonic acid, and 15 ohms for adenosine diphosphate. There were no significant differences in platelet aggregation responses to collagen, arachidonic acid, and adenosine diphosphate between uremic and control dogs. Hemorrhagic tendencies were not detected in uremic dogs by use of whole blood platelet aggregation. Results of this study suggest that platelet aggregation by use of the whole blood platelet aggregometer is not abnormal in uremic dogs, but does not exclude the possibility of a platelet aggregation defect undetected by the whole blood system.

Adenosine Diphosphate↗
PubMed2001

Effect of perezone, aminoperezone and their corresponding isomers isoperezone and isoaminoperezone upon in vitro platelet aggregation.

The effect on platelet aggregation of perezone, isoperezone, aminoperezone and isoaminoperezone has been determined in human platelets, using adenosinediphosphate (ADP), epinephrine and collagen as inducers. Perezone inhibited ADP- epinephrine- and collagen-induced platelet aggregation; isoperezone, aminoperezone and isoaminoperezone did not. The difference in biological responses could be the result of their structures. While isoperezone, aminoperezone and isoaminoperezone have carbonyl groups in the vicinity of other functional groups, this is not the case for perezone, in which one of the carbonyl groups has an adjacent free position.

Adenosine Diphosphate↗
PubMed2000

P-selectin expression on platelets determines size and stability of platelet aggregates.

BACKGROUND: P-selectin mediates rolling of platelets and leukocytes on activated endothelial cells. After platelet activation, P-selectin is translocated from intracellular granules to the external membrane, whereas fibrinogen aggregates platelets by bridging glycoprotein (GP) IIb/IIIa between adjacent platelets. METHODS AND RESULTS: In this study, we define a novel role for P-selectin in platelet aggregation. Expression of P-selectin on the platelet surface correlated strongly with the mean platelet aggregate size. Inhibition of P-selectin binding to its ligand by either monoclonal anti-P-selectin antibodies directed against the lectin domain or soluble human P-selectin reversed platelet aggregation even when added up to 5 minutes after activation; however, fibrinogen binding to platelets was not affected. This deaggregating effect significantly reduced the maximal size and number of platelet aggregates. When added 1 minute after platelet activation, anti-P-selectin antibody achieved 95% to 100% of the deaggregating effect of EDTA, whereas the anti-GP IIb/IIIa antibody abciximab had no effect. Monoclonal antibodies against known P-selectin ligands, such as P-selectin GP ligand-1 (PSGL-1) or GP Ib, had no effect on platelet aggregation, suggesting a different ligand for P-selectin in platelet aggregate stabilization. In kinetic studies, P-selectin was maximally expressed 10 minutes after platelet activation, whereas maximal activation of GP IIb/IIIa occurred within the first 10 seconds, suggesting that P-selectin operates after fibrinogen binding to activated GP IIb/IIIa. CONCLUSIONS: These results indicate that P-selectin interaction with a ligand, different from PSGL-1 or GP Ib, stabilizes initial GP IIb/IIIa-fibrinogen interactions, allowing the formation of large stable platelet aggregates.

Abciximab↗
PubMed1985

Platelet aggregation and evaluation of the ratio thromboxane B2/6-keto-prostaglandin F1 alpha in the plasma of patients on long term cimetidine treatment.

It has been reported that a long term treatment with cimetidine may give rise to thrombotic complications and may cause reversible damage to blood cells. In 57 patients on long term cimetidine treatment, platelet aggregates, platelet aggregation in vitro, plasma 6-keto-PGF1 alpha/thromboxane B2 ratio and platelet cyclic AMP levels were assessed. In 52% of the patients, platelet aggregate ratios were abnormal and collagen and ADP-hypersensitive platelets were observed. Such alterations began occurring after the first month of therapy and were shown to worsen progressively during the administration. Four of these patients, who developed unexpected thrombotic compliances after about 7 months of therapy, showed higher than normal plasma thromboxane B2, lower plasma 6-keto-PGF1 alpha and two of them, lower platelet cyclic AMP concentrations. It is suggested that cimetidine, through an unknown mechanism which probably involves activation of endogenous cyclic AMP phosphodiesterase, may favour the action of platelet aggregating agents.

6-Ketoprostaglandin F1 alpha↗
PubMed2002

Determination of platelet aggregation inhibition during percutaneous coronary intervention with the platelet function analyzer PFA-100.

BACKGROUND: A simple device to rapidly evaluate platelet function may aid in optimizing glycoprotein IIb/IIIa inhibition during percutaneous coronary intervention (PCI). We prospectively studied platelet function in 250 patients receiving abciximab or eptifibatide during PCI. METHODS AND RESULTS: The platelet function analyzer PFA-100 (Dade-Behring, Deerfield, Ill) measures platelet function by determining the time to occlusion of an aperture in a biochemically active membrane as whole blood flows under high shear conditions. Platelet aggregation causes aperture occlusion, and results are reported as a closure time (CT). All patients received either abciximab or eptifibatide, along with aspirin and heparin; patients undergoing stent implantation received aspirin and a thienopyridine postprocedure. The CT was measured at baseline and 10 minutes, 4 hours, 12 hours (abciximab-only), and 24 hours after the bolus. Profound inhibition was exhibited in most patients shortly after the platelet inhibitor bolus and during the course of therapy. We observed recovery of platelet function 12 hours after discontinuation of abciximab, with a high degree of interpatient variability, and ongoing profound platelet inhibition 4 to 6 hours after the discontinuation of eptifibatide. Among patients treated with abciximab, patients who were obese recovered from platelet inhibition sooner than patients who were not obese, whereas patients who were elderly had delayed recovery compared with patients who were not elderly. Failure to achieve maximal platelet inhibition (nonclosure) at 10 minutes indicated a possible association with adverse clinical events at the 6-month follow-up examination (60% vs 20%). CONCLUSIONS: PFA-100 is a rapid simple assay used as a means of assessing inhibition of platelet aggregation during PCI performed with glycoprotein IIb/IIIa inhibition. Failure to achieve nonclosure early after the initiation of abciximab therapy warrants further investigation because there may be an association with adverse cardiac events at 6-month follow-up.

Abciximab↗
PubMed1975

[Liberation of anti-heparin activity during platelet aggregation in patients with blastic leukosis and blastic crisis of chronic myelosis].

The activity of platelet factor 4 (FP4) was examined in 37 patients affected with blastic leukaemia, in 16 patients with blastic crisis in chronic myeloid leukaemia and in 2 patients with Willebrand's syndrome. The real activity of FP4 determined by modifying the method according to NIEWIAROWSKI after a complete lysis of granular membrances by means of triton X-100 was found to be lowered in 9 patients affected with blastic leukaemia, in 5 patients with blastic crisis and in two patients with Willebrand's syndrome. Presuming that a maximal FP4 release of the irreversible platelet aggregation must be obtained, which corresponds to the real activity, the author has examined the apparent activity of FP4 released from the aggregated platelets with the help of her own method. In this way the quality of the release reaction from the platelets can indirectly be characterized with their extremely important role for haemostasis. Whereas in exacerbated myeloid leukaemia and Willebrand's syndrome the apparent activity will correspond to the real one, there is a severe specific disturbance of the platelet release response in blastic leukaemia. The platelet aggregation is incomplete caused by the derailment of the energy metabolism and the disturbance of the adenine nucleotides, thus causing an apparent as well as a real FP4 deficiency which can be brought into the same line with pathogenesis of thrombopathy in blastic leukaemia.

Blood Coagulation Factors↗
PubMed1990

Inhibition of rabbit platelet aggregation by 1,4-naphthoquinones.

The effects of four 1,4-naphthoquinone derivatives on the aggregation of rabbit platelets were examined. All the four 1,4-naphthoquinone derivatives inhibited the platelet aggregation of washed rabbit platelets induced by thrombin (0.1 U/ml) and the IC50 is: 2-chloro-3-methyl-1,4-naphthoquinone (CMN), 5 micrograms/ml; 3-methyl-5,8-dihydroxy-1,4-naphthoquinone, 13 micrograms/ml; 5,8-dihydroxy-1,4-naphthoquinone, 18 micrograms/ml; 3-methyl-1,4-naphthoquinone (vitamin K3), 53 micrograms/ml. CMN was the most potent in inhibiting the aggregation and release reaction induced by ADP, arachidonic acid, PAF, ionophore A23187, collagen and thrombin in a dose-dependent manner in washed platelets, platelet-rich-plasma and whole blood. The thromboxane B2 formation caused by collagen and ionophore A23187 was inhibited by CMN. However, the thromboxane B2 formation by arachidonic acid was markedly increased. The platelet inhibitory effect of CMN could not be antagonized either by raising the concentrations of extracellular Ca++ or by wash out. The phosphoinositides breakdown induced by thrombin was inhibited by CMN. Phospholipids (PE, PC, PI) could slightly antagonize the antiplatelet effect of CMN. It is concluded that the inhibitory effect of CMN on rabbit platelet aggregation may be due to the inhibition of phosphoinositides breakdown caused by the inducers.

Adenosine Diphosphate↗
PubMed1986

Platelet aggregation and plasma lipoproteins in alcoholics during alcohol withdrawal.

Platelet aggregation, platelet lipid composition and plasma lipoprotein concentrations were measured each week in a group of seventeen alcoholics, without overt liver disease, for one month, following acute, total alcohol withdrawal. The platelets were initially hypoaggregable but, within 1-2 weeks of cessation of drinking, they became hyperaggregable and then gradually returned towards normal values. Hyperaggregability could not be explained by increases in either the cholesterol or the arachidonic acid content of the platelets. Plasma very-low-density lipoprotein cholesterol levels remained high throughout the study, but the initially raised levels of high-density lipoprotein (HDL) cholesterol fell by 26%. Low-density lipoprotein (LDL) cholesterol concentration rose by 10% after two weeks of withdrawal but then returned to about the starting level. The resulting changes in the plasma LDL-cholesterol:HDL-cholesterol ratio, which had increased by more than 50% after two weeks of abstinence, essentially paralleled the time course of enhanced platelet reactivity in all but four of the alcoholics. These findings suggest that alterations in plasma lipoprotein concentrations during acute alcohol withdrawal may be a contributory factor to the haemostatic disorders present in such patients.

Adult↗
PubMed1995

[Detection of platelet aggregates using light scattering].

Platelets play an important role in hemostasis and thrombosis. Evaluation of platelet function provides useful information on the diagnosis and cure of diseases associated with hemostasis and thrombosis. Among various platelet functions, platelet aggregometry is most widely used in clinical application. Platelet aggregation has been assessed by measuring the changes in the optical density of the platelet suspensions. However, this method has several shortcomings such as failure to detect the formation of small aggregates and lack of correlation between aggregate formation and changes in optical density. Thus, we have developed a new method of platelet aggregometry based on light scattering. This device emits laser beams against platelet aggregates and efficiently detects light scattering produced by these aggregates. The intensity and frequency of light scattering provides information as to the size and number of aggregates present in a limited area. By this method, we were able to determine several different modes of inhibitory effects on platelet aggregation. The high sensitivity of this method also allowed us to detect slight platelet activation, which had not been possible by the conventional method using changes in optical density. Clinical application of this method revealed frequent occurrence of spontaneous aggregation in diabetic patients and a close relationship between this phenomenon and diabetic complications.

Diabetes Mellitus↗
PubMed2006

Ingestion of onion soup high in quercetin inhibits platelet aggregation and essential components of the collagen-stimulated platelet activation pathway in man: a pilot study.

Epidemiological data suggest that those who consume a diet rich in quercetin-containing foods may have a reduced risk of CVD. Furthermore, in vitro and ex vivo studies have observed the inhibition of collagen-induced platelet activation by quercetin. The aim of the present study was to investigate the possible inhibitory effects of quercetin ingestion from a dietary source on collagen-stimulated platelet aggregation and signalling. A double-blind randomised cross-over pilot study was undertaken. Subjects ingested a soup containing either a high or a low amount of quercetin. Plasma quercetin concentrations and platelet aggregation and signalling were assessed after soup ingestion. The high-quercetin soup contained 69 mg total quercetin compared with the low-quercetin soup containing 5 mg total quercetin. Plasma quercetin concentrations were significantly higher after high-quercetin soup ingestion than after low-quercetin soup ingestion and peaked at 2.59 (sem 0.42) mumol/l. Collagen-stimulated (0.5 mug/ml) platelet aggregation was inhibited after ingestion of the high-quercetin soup in a time-dependent manner. Collagen-stimulated tyrosine phosphorylation of a key component of the collagen-signalling pathway via glycoprotein VI, Syk, was significantly inhibited by ingestion of the high-quercetin soup. The inhibition of Syk tyrosine phosphorylation was correlated with the area under the curve for the high-quercetin plasma profile. In conclusion, the ingestion of quercetin from a dietary source of onion soup could inhibit some aspects of collagen-stimulated platelet aggregation and signalling ex vivo. This further substantiates the epidemiological data suggesting that those who preferentially consume high amounts of quercetin-containing foods have a reduced risk of thrombosis and potential CVD risk.

Adult↗