thromboxane-a2 and Blood-Platelet-Disorders

The exact etiology of the conflicting hemostatic disorder in the advanced stage of chronic renal disease, i.e. prothrombotic versus bleeding tendency, is not completely understood. Abnormal platelet function in patients with renal failure is not caused by high concentrations of urea, although the presence of fibrinogen fragments may prevent binding of normal fibrinogen and formation of platelet aggregates. Hemostatic abnormalities in end-stage kidney disease may be affected, to some extent, by the choice of renal replacement therapy. Patients on hemodialysis have an increased risk of thrombotic events, primarily due to the release of thromboxane A2 and adenosine diphosphate into the circulation, as well as platelet degranulation. Some activation of platelets occurs due to the exposure of blood to the roller pump segment, but microbubbles may also play a role. Renal transplantation is the treatment of choice for patients with end-stage renal disease. Immunosuppressive therapy is associated with an increased risk of thromboembolic complications. Additional research is required to identify the potential benefits of different immunosuppressive therapies in relation to platelet aggregation, keeping in mind the long- term need for immunosuppression in renal transplant patients.

Topics: Adenosine Diphosphate; Blood Platelet Disorders; Humans; Kidney Failure, Chronic; Kidney Transplantation; Platelet Aggregation; Renal Dialysis; Renal Replacement Therapy; Risk Factors; Thromboembolism; Thrombosis; Thromboxane A2

Topics: Amino Acid Sequence; Blood Platelet Disorders; Genes, Dominant; Humans; Molecular Sequence Data; Receptors, Thromboxane; Thromboxane A2

Topics: Blood Platelet Disorders; Blood Platelets; Humans; Prostaglandin-Endoperoxide Synthases; Thromboxane A2

Topics: Blood Coagulation Disorders; Blood Platelet Disorders; Blood Platelets; Heterozygote; Humans; Platelet Aggregation; Syndrome; Thromboxane A2; Thromboxanes; von Willebrand Diseases

Platelet membranes play a key role in all stages of the haemostatic mechanism. Four of these in particular are considered here: adhesion to subendothelium, which involves an interaction between the glycoprotein I complex in the platelet membrane (deficient in the Bernard-Soulier syndrome) and plasma factor VIII; aggregation, involving the membrane glycoprotein IIb/IIIa complex (deficient in thrombasthenia), plasma fibrinogen and divalent cations; platelet factor 3 availability, a function of surface membrane phospholipids; and thromboxane synthesis, a function of the phospholipids of the membrane of the dense tubular system. The glycoprotein I complex also carries binding sites for thrombin and for drug-dependent antibodies, and glycoprotein IIb/IIIa is the site of the P1A1 antigen and of alpha-actinin.

Topics: Blood Platelet Disorders; Blood Platelets; Cell Adhesion; Cell Membrane; Connective Tissue; Hemostasis; Humans; Platelet Aggregation; Platelet Factor 3; Prostaglandin Endoperoxides; Thromboxane A2; von Willebrand Diseases

Light transmission aggregometry (LTA) is used worldwide for the investigation of heritable platelet function disorders (PFDs), but interpretation of results is complicated by the feedback effects of ADP and thromboxane A(2) (TxA(2)) and by the overlap with the response of healthy volunteers. Over 5 years, we have performed lumi-aggregometry on 9 platelet agonists in 111 unrelated research participants with suspected PFDs and in 70 healthy volunteers. Abnormal LTA or ATP secretion test results were identified in 58% of participants. In 84% of these, the patterns of response were consistent with defects in Gi receptor signaling, the TxA(2) pathway, and dense granule secretion. Participants with defects in signaling to Gq-coupled receptor agonists and to collagen were also identified. Targeted genotyping identified 3 participants with function-disrupting mutations in the P2Y(12) ADP and TxA(2) receptors. The results of the present study illustrate that detailed phenotypic analysis using LTA and ATP secretion is a powerful tool for the diagnosis of PFDs. Our data also enable subdivision at the level of platelet-signaling pathways and in some cases to individual receptors. We further demonstrate that most PFDs can be reliably diagnosed using a streamlined panel of key platelet agonists and specified concentrations suitable for testing in most clinical diagnostic laboratories.

Topics: Adenosine Triphosphate; Adolescent; Adult; Blood Platelet Disorders; Blood Platelets; Child; Female; Genotype; Humans; Male; Middle Aged; Mutation; Platelet Aggregation; Platelet Function Tests; Platelet Membrane Glycoproteins; Receptors, Purinergic P2Y12; Receptors, Thromboxane A2, Prostaglandin H2; Secretory Vesicles; Signal Transduction; Thromboxane A2; Young Adult

Aspirin-like defect (ALD) is a rare, mostly autosomal dominant inherited dysfunction of the intraplatelet arachidonic acid (AA) pathway leading to impaired thromboxane A2 signalling. We aimed to establish diagnostic criteria for ALD diagnosis and present clinical and laboratory phenotypes of 52 individuals from 17 unrelated families. Platelet in vitro function was determined on the basis of platelet aggregation response (PAR) to AA, adenosine diphosphate, collagen and ristocetin as well as PFA-100 closure times (CT). Using impaired PAR to AA (< or =10%) as the mandatory diagnostic criterion, ALD could be confirmed in 17 patients. Subsequently, family members were investigated and among 35 individuals an additional 13 ALD patients as well as 4 individuals with mild ALD (PAR to AA: 19-32%) were identified. At least one bleeding symptom was reported by 25 (74%) ALD patients and prolonged CT was detected in 24 (71%) of the cases, both significantly correlated with impaired PAR to AA (P = 0.001 and P = 0.002, respectively). An estimated 0.6% prevalence was determined for ALD in our paediatric patients with suspected coagulation disorders. Due to the mild bleeding symptoms, ALD is probably underdiagnosed. If ALD is suspected, PAR to AA is suitable for the identification of individuals at risk of increased haemorrhage.

Topics: Adolescent; Adult; Arachidonic Acid; Bleeding Time; Blood Platelet Disorders; Blood Platelets; Case-Control Studies; Chi-Square Distribution; Child; Child, Preschool; Female; Hemostatic Disorders; Humans; Male; Middle Aged; Phenotype; Platelet Aggregation; Platelet Function Tests; Prostaglandin-Endoperoxide Synthases; Signal Transduction; Syndrome; Thromboxane A2; Young Adult

Topics: Adenosine Diphosphate; Adult; Blood Platelet Disorders; Collagen; Female; Humans; Platelet Aggregation; Pregnancy; Siblings; Thromboxane A2

An Arg60-to-Leu mutation was found in the first cytoplasmic loop of the PLT TxA2 receptor as a new congenital PLT disorder characterized by impaired responsiveness to TxA2. However, it has not been clarified whether DDAVP is effective in correcting the bleeding time (BT) in this PLT disorder.. DDAVP (0.4 microg/kg) was intravenously administered over 20 minutes in five patients with this PLT disorder, and template BT, PLT retention to glass beads, PLT aggregation, and a coagulation study were performed before and after the infusion of DDAVP. PLT TxA2 synthesis defects (cyclo-oxygenase deficiency, volunteers taking aspirin), thrombasthenia, and Bernard-Soulier syndrome were also included in this study.. The normalization of BT was found in all patients with this PLT disorder, and one of the patients successfully underwent oral surgical procedures with DDAVP as the only hemostatic agent. DDAVP was also efficacious in the TxA2 synthesis defect but not in other disorders. FVIII coagulation activity, vWF antigen, and ristocetin cofactor significantly increased in all patients after DDAVP, but no changes were seen in the PLT retention rate and PLT aggregation study after DDAVP infusion.. DDAVP was effective in correcting BT in patients with impaired responsiveness to TxA2 as well as impaired production of TxA2.

Topics: Bleeding Time; Blood Coagulation Factors; Blood Platelet Disorders; Blood Platelets; Deamino Arginine Vasopressin; Female; Hemostatics; Humans; Middle Aged; Periodontal Cyst; Preoperative Care; Receptors, Thromboxane; Thromboxane A2; Tooth Extraction

We report three cases of platelet dysfunction characterized by defective Ca2+ ionophore-induced platelet aggregation without impaired production of thromboxane A2 (TXA2). The patients had mild to moderate bleeding tendencies, and their platelet aggregation and secretion induced by ADP, collagen, arachidonic acid, stable TXA2 (STA2) and Ca2+ ionophore A23187 was defective or much reduced. However, ristocetin- or thrombin-induced platelet aggregation was normal. The analysis of second messenger formation showed that inositol 1,4,5-triphosphate formation or Ca2+ mobilization induced by thrombin, STA2 or A23187 was normal. Furthermore, the phosphorylation of 47 kDa protein (pleckstrin) and 20 kDa protein (myosin light chain, MLC) in response to those agonists was normal. These findings suggest that the defective site in the patients' platelets lies in the process distal to or independent of protein kinase C activation, Ca2+ mobilization and MLC phosphorylation.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Adult; Arachidonic Acid; Blood Platelet Disorders; Blood Proteins; Calcimycin; Calcium; Collagen; Female; Humans; Ionophores; Male; Middle Aged; Myosin Light Chains; Phosphoproteins; Phosphorylation; Platelet Aggregation; Platelet Membrane Glycoproteins; Ristocetin; Thrombin; Thromboxane A2

Physiological concentrations of low-density lipoprotein (LDL) sensitize blood platelets to alpha-thrombin- and collagen-induced secretion, and after prolonged contact trigger secretion independent of other agonists. Here we report that LDL activates the small GTPases Rap1 and Ral but not Ras, as assessed by specific precipitation of the GTP-bound enzymes. In unstirred suspensions, the inhibitor SB203580 blocks Rap1 activation by 60-70%, suggesting activation via p38 mitogen-activated protein kinase and a second, unidentified route. Inhibitors of cyclooxygenase (indomethacin) and the thromboxane A(2) (TxA(2)) receptor (SQ30741) induce complete inhibition, indicating that Rap1 activation is the result of TxA(2) formation. Stirring reveals a second, TxA(2)-independent Rap1 activation, which correlates quantitatively with a slow induction of dense granule secretion. Both pathways are unaffected by inhibitors of ligand binding to integrin alpha(IIb)beta(3). The results suggest that Rap1 and Ral, but not Ras, may take part in signalling routes initiated by LDL that initially enhance the sensitivity of platelets to other agonists and later trigger LDL-dependent secretion.

Topics: Arachidonic Acid; Blood Platelet Disorders; Blood Platelets; Collagen; Cyclooxygenase Inhibitors; Dose-Response Relationship, Drug; Enzyme Activation; Enzyme Inhibitors; Glutathione Transferase; Humans; Imidazoles; Indomethacin; Ligands; Lipoproteins, LDL; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinases; p38 Mitogen-Activated Protein Kinases; Phospholipases A; Phosphorylation; Pyridines; ral GTP-Binding Proteins; rap1 GTP-Binding Proteins; Recombinant Fusion Proteins; Signal Transduction; Thrombin; Thromboxane A2; Time Factors

Two unrelated patients with a congenital bleeding diathesis associated with a severe defect of the platelet ADP receptor coupled to adenylate cyclase (P2(CYC)) have been described so far. In one of them, platelet secretion was shown to be abnormal. We recently showed that platelets with the primary secretion defect (PSD; characterized by abnormal secretion but normal granule stores, thromboxane A(2) production, and ADP-induced primary wave of aggregation) have a moderate defect of P2(CYC). Therefore, the interaction of ADP with the full complement of its receptors seems to be essential for normal platelet secretion, and PSD patients may be heterozygotes for the congenital severe defect of P2(CYC). In this study, we describe 2 new related patients with a severe defect of P2(CYC) and the son of one of them, who is to be considered an obligate heterozygote for the defect. The 2 patients with the severe defect had lifelong histories of abnormal bleeding, prolonged bleeding times, abnormalities of platelet aggregation and secretion, lack of inhibition of adenylate cyclase by ADP, and a deficiency of platelet-binding sites for [(33)P]2 MeS-ADP (240 and 225 sites per platelet; normal range, 530 to 1102). The son of one of them had a mildly prolonged bleeding time and abnormalities of platelet aggregation and secretion similar to those found in patients with PSD. In addition, his platelets showed a moderate defect of binding sites for [(33)P]2 MeS-ADP (430 sites per platelet) and of adenylate cyclase inhibition by ADP. This study of a family with the platelet disorder characterized by a defect of the platelet P2(CYC) receptor supports our hypothesis that the full complement of the platelet ADP receptors is essential for normal platelet secretion and that some patients with the common, ill-defined diagnosis of PSD are actually heterozygous for the defect.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Adolescent; Adult; Blood Platelet Disorders; Blood Platelets; Cytoplasmic Granules; Female; Genetic Carrier Screening; Humans; Male; Middle Aged; Platelet Aggregation; Receptors, Purinergic P2; Thromboxane A2

Human platelet thromboxane A2 (TXA2) receptor (TXR) has been reported to functionally couple to the inhibitory GTP-binding protein for adenylyl cyclase (Gi). However, it still remains unclear which portions of the TXR structure are critical determinants in that coupling. We have previously reported several patients with platelet dysfunction, whose platelets showed impaired coupling between TXR and phospholipase C caused by an Arg60 to Leu mutation in the first cytoplasmic loop. To investigate whether this portion is essential for mediating inhibitory coupling between TXR and adenylyl cyclase, we analyzed the inhibition by the TXA2 analog of the PGE1 or forskolin-induced platelet cAMP increase in patients' platelets, and found that the inhibition occurred normally. This suggests that Arg60 in the first cytoplasmic loop of the TXR is not involved in TXR-Gi coupling.

Topics: Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Adult; Alprostadil; Amino Acid Substitution; Arginine; Blood Platelet Disorders; Blood Platelets; Colforsin; Cyclic AMP; Cytoplasm; Female; Humans; Leucine; Male; Middle Aged; Mutation, Missense; Peptide Fragments; Protein Structure, Tertiary; Receptors, Thromboxane; Thromboxane A2

Previously, we reported five cases of platelet dysfunction characterized by the absence of thromboxane A2 (TXA2) - induced platelet aggregation despite normal TXA2 binding activity. In this platelet disorder, patients were divided into two groups; i.e. those whose platelets lacked or did not lack phospholipase C (PLC) activation (Group A and Group B, respectively) (Thromb Haemost 1996; 76: 1080). Furthermore, in one of the patients, we showed that a single amino acid substitution (Arg60 to Leu) in the first cytoplasmic loop of the TXA2 receptor (TXR) was responsible for this platelet disorder. However, mutational analysis of the TXR in the remaining patients has not been performed. Based on this background, we investigated the mutations of the TXR in these patients, and found that all of the patients have the same abnormality of the TXR (Arg60-->Leu), although the Group A patients were homozygous and the Group B patients were heterozygous for this mutation. This mutation is the only abnormality which has been found in this platelet disorder, and in patients heterozygous for this mutation, the mutant type TXR suppresses wild-type receptor-mediated platelet aggregation by a mechanism independent of PLC activation.

Topics: Adult; Amino Acid Substitution; Blood Platelet Disorders; Blood Platelets; Female; Genotype; Humans; Middle Aged; Phosphatidylinositol Diacylglycerol-Lyase; Platelet Aggregation; Point Mutation; Receptors, Thromboxane; Thromboxane A2; Type C Phospholipases

By the term "Primary Secretion Defect" (PSD), we mean a common heterogeneous group of congenital defects of platelet secretion, characterized by a normal primary wave of platelet aggregation induced by ADP and other agonists, a normal concentration of platelet granule contents, and normal production of thromboxane A2. The biochemical abnormalities responsible for PSD are not well known. Since a secretion defect similar to PSD is found in platelets that are severely deficient of binding sites for the ADP analogue 2MeS-ADP and do not aggregate in response to ADP, we tested the hypothesis that PSD platelets have moderately decreased 2MeS-ADP binding sites, which may be sufficient for normal ADP-induced aggregation but not for potentiating platelet secretion. The specific binding of [33P]2MeS-ADP to platelets from 3 PSD patients (347, 443 and 490 sites/platelet; KD 2.8-3.9 nM) was lower than to platelets from 24 normal subjects (647 [530-1102]; KD = 3.8 [2.3-7.3]) (median [range]). Normal values were found in a fourth PSD patient (710; KD 3.7). The degree of inhibition of PGE1-induced cAMP increase by 0.1 microM ADP was lower in patients than in controls. The secretion induced by the endoperoxide analogue U46619 from normal, acetylsalicylic acid-treated platelets under conditions that prevented the formation of large aggregates was potentiated by 1 mumol/l ADP and inhibited by apyrase. These findings indicate that a partial deficiency of the platelet ADP receptor(s) might be responsible for the defect of platelet secretion in some PSD patients and that ADP potentiates platelet secretion independently of the formation of large aggregates and thromboxane A2 production.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Adult; Binding Sites; Blood Platelet Disorders; Blood Platelets; Cytoplasmic Granules; Female; Fibrinogen; Humans; In Vitro Techniques; Kinetics; Male; Middle Aged; Phosphorus Radioisotopes; Platelet Aggregation; Reference Values; Serotonin; Thionucleotides; Thromboxane A2

We describe an 11-year-old girl with a mild bleeding disorder since early childhood. The disorder was characterized by a prolonged bleeding time, and the patient's platelets showed defective aggregation responses to thromboxane A2 (TXA2) mimetic U46619 and arachidonic acid. In contrast, the platelets showed normal responses to thrombin and Ca ionophore A23187. When the platelet TXA2 receptor was examined with the [3H]-labeled TXA2 agonist U46619, the equilibrium dissociation rate constants (kd) and the maximal concentration of binding sites (Bmax) of the patient's platelets were within normal ranges. Normal GTPase activity was also induced in the patient's platelets by stimulation with U46619, however, inositol 1,4,5-triphosphate (IP3) formation was not induced by U46619. These results suggests that the patient's platelets had a defect in phospholipase C activation beyond TXA2 receptors.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Blood Platelet Disorders; Blood Platelets; Calcimycin; Child; Female; GTP Phosphohydrolases; GTP-Binding Proteins; Humans; In Vitro Techniques; Inositol 1,4,5-Trisphosphate; Kinetics; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Receptors, Thromboxane; Signal Transduction; Thrombin; Thromboxane A2; Type C Phospholipases

Five patients with mild bleeding tendencies characterized by defective thromboxane A2 (TXA2)-induced platelet aggregation are reported. The platelets of all the patients had the ability to bind exogenous TXA2. Bleeding time was markedly prolonged in one patient. In three of the five patients, synthetic TXA2 mimetic (STA2)-induced platelet responses, including IP3 formation, Ca2+ mobilization, phosphatidic acid formation and GTPase activities were selectively defective, suggesting impaired coupling between the TXA2 receptor and phospholipase C activation. However, in the remaining two patients, these responses were all within normal limits. This suggests that the defective site of this type of platelet disorder is heterogenous and that signaling mechanisms other than the TXA2 receptor-phospholipase C pathway are also involved in TXA2-induced platelet aggregation.

Topics: Adult; Binding Sites; Blood Platelet Disorders; Blood Platelets; Female; Humans; Male; Middle Aged; Platelet Aggregation; Receptors, Thromboxane; Thromboxane A2

Recent advances in molecular genetics have revealed the mechanisms underlying a variety of inherited human disorders. Among them, mutations in G protein-coupled receptors have clearly demonstrated two types of abnormalities, namely loss of function and constitutive activation of the receptors. Thromboxane A2 (TXA2) receptor is a member of the family of G protein-coupled receptors and performs an essential role in hemostasis by interacting with TXA2 to induce platelet aggregation. Here we identify a single amino acid substitution (Arg60-->Leu) in the first cytoplasmic loop of the TXA2 receptor in a dominantly inherited bleeding disorder characterized by defective platelet response to TXA2. This mutation was found exclusively in affected members of two unrelated families with the disorder. The mutant receptor expressed in Chinese hamster ovary cells showed decreased agonist-induced second messenger formation despite its normal ligand binding affinities. These results suggest that the Arg60 to Leu mutation is responsible for the disorder. Moreover, dominant inheritance of the disorder suggests the possibility that the mutation produces a dominant negative TXA2 receptor.

Topics: Amino Acid Sequence; Animals; Arginine; Base Sequence; Blood Platelet Disorders; Bridged Bicyclo Compounds; CHO Cells; Cloning, Molecular; Cricetinae; DNA Mutational Analysis; Fatty Acids, Monounsaturated; Female; Gene Expression; Genes, Dominant; Genotype; Humans; Male; Molecular Sequence Data; Platelet Aggregation; Point Mutation; Protein Conformation; Receptors, Thromboxane; Thrombin; Thromboxane A2

The phosphorylation responses of platelet proteins after platelet stimulation with agonists were studied in patients with clinical bleeding disorders and various types of impaired platelet functional responses. Impaired collagen-induced phosphorylation, particularly of the 47 kd substrate (P47) for protein kinase C, was observed in one patient whose platelet defect appears to be an impaired initial response to weak platelet agonists but whose platelet secretory mechanism is normal. Reduced phosphorylation of a 31 kd polypeptide was also observed. The phosphorylation defect in this patient differs from that seen in another patient in whom impaired P47 and myosin light chain phosphorylation was observed but whose functional defect may be more closely related to secretion. The results provide further evidence that phosphorylation of P47 may play a role in platelet activation mechanisms preceding secretion and that abnormalities of phosphorylation of both P47 and myosin light chain may be associated with platelet functional defects in some patients with bleeding disorders.

Topics: Adenosine Diphosphate; Blood Platelet Disorders; Blood Platelets; Blood Proteins; Collagen; Edetic Acid; Epinephrine; Erythrocyte Aggregation; Humans; Myosins; Phosphoproteins; Phosphorylation; Platelet Storage Pool Deficiency; Prostaglandin Endoperoxides, Synthetic; Thromboxane A2

Topics: Blood Platelet Disorders; Diagnosis, Differential; Humans; Infant, Newborn; Male; Pedigree; Platelet Aggregation; Thromboxane A2; Vitamin K Deficiency Bleeding

We identified SPA in three young apparently healthy women. SPA was associated with release of TXA2 and was only partially inhibited by ADP-inhibitor apyrase and alpha 2-adrenoceptor blocker yohimbine. In vitro incubation of aspirin (90 micrograms/ml) or selective TXA2 synthetase inhibitor OKY-046 (0.1 uM) with platelet rich plasma (PRP) did not abolish SPA, although platelet generation of TXA2 was markedly inhibited. In contrast, oral administration of large amounts of aspirin in one subject or in vitro incubation of PRP with TXA2 -endoperoxide receptor blocker SQ 29,548 (20-100 nM) significantly inhibited SPA. These studies suggest that SPA is associated with TXA2 release. Since TXA2 -endoperoxide receptor blocker completely abolishes the secondary wave, agents like this may be of therapeutic value in individuals with SPA and evidence of tissue ischemia.

Topics: Adult; Apyrase; Aspirin; Blood Platelet Disorders; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Fatty Acids, Unsaturated; Female; Humans; Hydrazines; In Vitro Techniques; Methacrylates; Platelet Aggregation; Thromboxane A2; Yohimbine

Topics: Albumins; Blood Platelet Disorders; Blood Platelets; Humans; Thromboxane A2

Topics: Adult; Blood Platelet Disorders; Blood Platelets; Female; Humans; Thromboxane A2

We demonstrate that zinc (0.1 to 0.3 mmol/L) induces aggregation of washed platelet suspensions. Higher concentrations (1 to 3 mmol/L) of zinc were needed to aggregate platelets in platelet-rich plasma obtained from blood anticoagulated with low-molecular-weight heparin, probably due to the binding of zinc to the plasma proteins. Zinc-induced aggregation of normal washed platelets required added fibrinogen and no aggregation occurred with thrombasthenic platelets or with normal platelets pretreated with a monoclonal antibody (10E5) that blocks the platelet fibrinogen receptor. These data indicate that the platelet membrane fibrinogen receptor-glycoproteins IIb and IIIa mediate the effect of zinc. Zinc-induced aggregation was blocked by the agent TMB-8, which interferes with the internal calcium flux, and by prostacyclin, which elevates platelet cyclic adenosine monophosphate levels. Zinc-induced aggregation was not accompanied by thromboxane synthesis or by the secretion of dense-body serotonin and was not affected by preexposure of platelets to acetylsalicylic acid. Experiments with creatine phosphate/creatine phosphokinase showed that the zinc effect on platelets was independent of extracellular adenosine diphosphate (ADP). Zinc had an additive effect when platelet aggregation was stimulated with subthreshhold concentrations of collagen or ADP. Together with the known effects of nutritional zinc on in vivo bleeding, on platelet aggregation, and on lipid metabolism, the results suggest that zinc may have an important bearing on normal hemostasis, thrombosis, and atherosclerosis.

Topics: Adenosine Diphosphate; Adult; Arachidonic Acid; Arachidonic Acids; Blood Platelet Disorders; Blood Platelets; Calcium; Collagen; Copper; Epoprostenol; Glycoproteins; Heparin; Humans; Manganese; Membrane Proteins; Platelet Aggregation; Platelet Membrane Glycoproteins; Receptors, Cell Surface; Serotonin; Thromboxane A2; Thromboxanes; Zinc

The authors describe a patient with a longstanding bleeding disorder associated with impaired platelet aggregation and secretion despite normal granule contents. Thrombin-induced platelet thromboxane A2 production, measured using a radioimmunoassay for thromboxane B2, was markedly decreased or undetectable in platelet-rich plasma and whole blood serum. However, significant amounts of thromboxane B2 were detected on thrombin stimulation of platelets suspended in albumin-free salt medium. Malondialdehyde and 14C-hydroxyheptadecatrienoic acid production was undetectable in the patient's platelets. Liberation of free 14C-arachidonic acid from phospholipids during stimulation of prelabeled platelets was normal, indicating normal phospholipase activity. These observations indicate an albumin-dependent partial deficiency in thromboxane production resulting from a defect either in cyclooxygenase or thromboxane synthetase. Further, the authors studied the effect of albumin on arachidonic acid metabolism in normal platelets. These studies indicate that albumin enhances liberation of arachidonic acid from phospholipids but has an overall inhibitory effect on thromboxane synthesis.

Topics: Adult; Albumins; Arachidonic Acid; Arachidonic Acids; Bleeding Time; Blood Platelet Disorders; Blood Platelets; Chromatography, Gel; Female; Hemorrhagic Disorders; Humans; Malondialdehyde; Partial Thromboplastin Time; Phospholipids; Platelet Aggregation; Platelet Count; Serotonin; Thrombin; Thromboxane A2; Thromboxane B2; Thromboxanes

Three family members from two successive generations had a bleeding tendency. Their template bleeding time was prolonged and platelet aggregation induced by ADP and adrenaline showed no second wave; collagen at low to moderate concentrations failed to aggregate and release ATP, whereas higher amounts aggregated and released. Aggregation and release due to thrombin, ristocetin, and synthetic epoxy derivatives (U 44069 and U 46619) were normal. Arachidonate (AA) was inactive, and was not converted either in thromboxane (TX) A2 activity evaluated on the rabbit aorta strip, nor in TXB2 evaluated by radioimmunoassay and by radiochromatography. The parallel impairment of TXB2 and PGE2 formation by the patient's platelets are compatible with a platelet cyclo-oxygenase deficiency. This study suggests that transmission is autosomal dominant, and confirms that cyclo-oxygenase is not needed for aggregation and ATP release by high amounts of collagen.

Topics: Adolescent; Adult; Arachidonic Acids; Bleeding Time; Blood Coagulation Tests; Blood Platelet Disorders; Blood Platelets; Child, Preschool; Dinoprostone; Female; Humans; Male; Platelet Aggregation; Prostaglandin-Endoperoxide Synthases; Prostaglandins E; Thromboxane A2; Thromboxane B2

A patient with a lifelong bleeding disorder is presented with a prolonged bleeding time and abnormal aggregation and secretion responses to arachidonic acid, thromboxane A2, PAF-acether and the divalent calcium ionophore A23187. Platelet alpha and dense granule contents and morphology appear normal. The proposed defect is due to an abnormality of a platelet intracellular calcium dependent process.

Topics: Arachidonic Acids; Bleeding Time; Blood Platelet Disorders; Calcimycin; Calcium; Female; Humans; Middle Aged; Nucleotides; Platelet Activating Factor; Platelet Aggregation; Thromboxane A2

A new type of acquired platelet dysfunction was found in a chronic myeloid leukaemia patient with petechiae and thrombocytosis. Platelet aggregation induced by arachidonic acid (AA), collagen and A23187 was decreased, secondary aggregation by ADP and epinephrine was defective and ristocetin-induced aggregation was completely reversible. No platelet ATP was released by AA and collagen. Only high concentrations of AA (greater than or equal to 2 mM) induced minimal reversible aggregation. 14C-serotonin uptake by the platelet and platelet adenine nucleotide contents were normal. Normal AA metabolism was demonstrated by thin-layer radiochromatographic analysis of the metabolites of 14C-AA and the determination of thiobarbituric acid reactive substances produced by the incubation of AA or thrombin with the platelets. Minimal reversible aggregation was observed when patient's platelet-rich plasma was added to a reaction mixture in which thromboxane A2 (TXA2) had been generated. TXA2 produced by patient's platelets showed normal platelet-aggregating activity. These results suggest that a subnormal platelet response to TXA2 is included as a mechanism for this acquired hypofunction of the platelet.

Topics: Adenosine Triphosphate; Arachidonic Acid; Arachidonic Acids; Blood Platelet Disorders; Blood Platelets; Female; Humans; Leukemia, Myeloid; Middle Aged; Platelet Aggregation; Platelet Function Tests; Thromboxane A2; Thromboxanes

To determine the pathogenetic mechanism of a hereditary primary platelet release disorder, arachidonic acid metabolism via the cyclooxygenase pathway was investigated. The propositus' platelets exhibited defective release reaction and second-wave aggregation when stimulated by sodium arachidonate or U46619, a thromboxane A2 (TXA2) agonist. The lack of platelet response to U46619 suggested that the defect was beyond the thromboxane synthetase level. Furthermore, thromboxane B2 (TXB2) formation in the propositus' platelets (558.52 ng/10(8) platelets) was within the normal range (574.29 +/- SD 27.39 ng/10(8) platelets) and TXA2 formation appeared to be adequate for aggregating normal platelets. The results were indicative of an abnormal platelet response to TXA2. Failure of the propositus' platelets to aggregate in response to TXA2 formed in normal platelet-rich plasma induced by arachidonate confirmed this notion. To gain further insight, platelet cyclic (c) AMP content was determined. Prostacyclin induced a significant elevation of the propositus' platelet cAMP level comparable to normal values. U46619 suppressed prostaglandin I2-induced cAMP elevation in normal subjects but had no such effect in the patient. We conclude that the primary release disorder observed in this kindred is due to an abnormal platelet respnse to TXA2 possibly because of TXA2/PGH2 receptor abnormalities.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adult; Arachidonic Acids; Blood Platelet Disorders; Blood Platelets; Cyclic AMP; Epoprostenol; Female; Humans; Platelet Aggregation; Prostaglandin Endoperoxides, Synthetic; Thromboxane A2; Thromboxanes

A new type of congenital platelet dysfunction was found in a young woman presenting a life-long bleeding disorder. The known types of thrombopathia and von Willebrand's disease were excluded by appropriate investigations. The platelets were morphologically normal, underwent normal shape change and contraction and synthesized thromboxane A2 (TXA2) normally. The release reaction was abnormal and the aggregation response to ADP, adrenalin, collagen, thrombin, sodium arachidonate and vasopressin was depressed due to decreased sensitivity of the platelets to prostaglandin endoperoxides and TXA2. Platelet cAMP content was increased.

Topics: Adolescent; Aspirin; Blood Coagulation Tests; Blood Platelet Disorders; Blood Platelets; Female; Humans; Platelet Aggregation; Serotonin; Thromboxane A2; Thromboxanes

Animal work suggests that with certain doses of aspirin the antithrombotic effect exerted via the inhibition of the proaggregatory platelet thromboxane A2 (TXA2) may be neutralised by the concomitant vascular reduction of the antiaggregatory prostacyclin (PGI2). Such a situation might result not only in therapeutic ineffectiveness but also in a thrombotic tendency. A patient with a bleeding disorder characterised by a mildly prolonged bleeding time and defective platelet-release reaction due to a congenital deficiency of cyclo-oxygenase provided an opportunity for studying this problem. Her platelets did not aggregate with arachidonic acid, but they did so with a synthetic endoperoxide analogue. Thrombin added to her platelet-rich plasma and whole blood did not generate thromboxane B2 (TXB2). Washed platelets, when incubated with 14C-arachidonic acid, did not produce the cyclo-oxygenase metabolites. A biopsy specimen of her vein did not generate PGI2, as measured both by platelet-aggregation inhibition and radioimmunoassay of 6-keto-PGF1 alpha. Clinically, the patient had a mild bleeding tendency but no thrombotic problems. The findings suggest that in man aspirin therapy, even at doses which inhibit PGI2 formation, would only impair haemostasis mildly without producing a thrombotic tendency.

Topics: Adenosine Diphosphate; Adult; Arachidonic Acids; Aspirin; Blood Coagulation Tests; Blood Platelet Disorders; Cells, Cultured; Chromatography, Thin Layer; Epoprostenol; Hemorrhage; Humans; Male; Oxygenases; Plasma; Platelet Aggregation; Prostaglandins; Thromboxane A2; Thromboxanes

Topics: Adenosine Diphosphate; Aged; Animals; Aorta; Arachidonic Acids; Blood Platelet Disorders; Blood Platelets; Calcimycin; Humans; Male; Muscle Contraction; Platelet Aggregation; Rabbits; Thromboxane A2

Platelet aggregation and the platelet prostaglandin pathway have been investigated in two patients with preleukaemic states who had a haemorrhagic tendency but a normal platelet count. In both patients platelet aggregation induced by collagen adenosine diphosphate (ADP) and arachidonic acid (AA) were abnormal. Malonyldiadehyde (MDA) production from exogenous AA was normal in both patients thus excluding cyclo-oxygenase deficiency. The platelet aggregating and rabbit aorta contracting activities of thromboxane A2 (TxA2) were very low in both patients. Production of thromboxane B2 (TxB2) assessed by thin layer chromatographic separation of the metabolites of [1(-14)C]AA and by radioimmunoassay, was normal. These abnormalities of platelet function appear to be due to the production of TxA2 with a low biological activity.

Topics: Adenine Nucleotides; Blood Platelet Disorders; Blood Platelets; Female; Humans; Male; Platelet Aggregation; Preleukemia; Thromboxane A2; Thromboxane B2; Thromboxanes

Two cases of thrombocytopathia with congenital deficiency of platelet cyclo-oxygenase were investigated. The platelet release reaction was impaired. There was a marked decrease of aggregation with collagen and with adrenalin and a total absence of aggregation with sodium arachidonate. The platelet response to labile aggregation stimulating substance (LASS, mostly thromboxane A2) was normal. There was no biosynthesis of prostaglandin cyclic endoperoxides or of thromboxane A2 from arachidonic acid. Basal levels of platelet PGE1 were lowered although plasma levels were normal. Thrombin decreased the cyclic AMP content of patients' platelets and also that of control platelets pretreated with aspirin. The patients platelets showed no ultrastructural difference when compared with control platelets, except for a slight decrease of granule volume, but, in contrast to control platelets, thrombin (0.02 U/ml) did not provoke contraction of the patients' platelets.

Topics: Adult; Blood Platelet Disorders; Blood Platelets; Cyclic AMP; Female; Humans; Microscopy, Electron; Middle Aged; Platelet Aggregation; Prostaglandin-Endoperoxide Synthases; Prostaglandins E; Prostaglandins F; Thrombin; Thromboxane A2; Thromboxane B2; Thromboxanes