thromboxane-b2 and von-Willebrand-Diseases

The blood volumes and concentrations of thromboxane B2 (TxB2), platelet factor 4 (PF4), and fibrinopeptide A (FPA) were measured every 30 seconds in bleeding-time blood in normal subjects and in patients with idiopathic thrombocytopenic purpura (ITP), delta and alpha delta storage pool deficiency (SPD), Bernard-Soulier Syndrome (BSS), thrombasthenia (TSA), and von Willebrand's disease (vWD). Data were fitted to second-order (TxB2, PF4, and FPA) or third-order (volumes) polynomials. Average values for various parameters over fixed-time intervals were determined by numerical methods. The bleeding time was greater than 15 minutes in all patient groups and the initial bleeding, as reflected by the initial slope of the fitted blood volume curves, was increased in ITP, BSS, and SPD (delta-SPD in particular), but not in vWD and TSA. The increased values for both the initial slope and the volume of blood collected after 2 minutes in SPD suggest that vascular tone may be modulated, in part, by dense granule substances such as adenosine triphosphate (ATP) or serotonin. In TSA, uniquely, both platelet (TxB2 and PF4) and coagulation (FPA) values were increased in early bleeding samples (initial slope). In vitro studies of TxB2 production, together with previous flow studies of fibrin formation, also suggest enhanced activation and coagulant properties of thrombasthenic platelets. In other patients, reduced values of all substances at later times may reflect impaired platelet-fibrin plug formation in the high-shear regions at the ends of transected blood vessels. However, the initial slopes of the fitted curves for both TxB2 and PF4 were normal in vWD, suggesting that the early appearance of these substances may typically be from platelets that are adherent to collagen within the lower shear environment of the wound surface. The finding that FPA values were not decreased initially in any patient group, including ITP, but were decreased at later times (except for TSA), suggests that early fibrin formation occurs independently of platelets in the low-shear environment of the wound surface, whereas at later times fibrin is formed in a platelet-dependent manner in the high-shear regions at the ends of transected vessels.

Topics: Adult; Bernard-Soulier Syndrome; Bleeding Time; Blood Platelet Disorders; Fibrinopeptide A; Humans; Kinetics; Middle Aged; Platelet Factor 4; Platelet Membrane Glycoproteins; Platelet Storage Pool Deficiency; Purpura, Thrombocytopenic, Idiopathic; Thromboxane B2; von Willebrand Diseases

The ability of certain strains of Streptococcus sanguis to aggregate human platelets in vitro may be related to their virulence in the pathogenesis of infective endocarditis. We have studied the mechanisms of aggregation of human platelets by S. sanguis strain NCTC 7863. Platelet aggregation follows incubation of S. sanguis cells with platelet-rich plasma from normal, healthy adults, after a lag of 7-19 min. Platelet aggregation was accompanied by 5-hydroxytryptamine release and thromboxane B2 production. Aggregation was prevented by aspirin and by EDTA. Platelets from two patients with Glanzmann's thrombasthenia did not respond to bacteria. Fixed, washed platelets resuspended in normal plasma were not agglutinated by S. sanguis. Blocking the glycoprotein Ib receptor with a monoclonal antibody inhibited aggregation of PRP. However, S. sanguis did not induce von Willebrand factor (vWF) binding to platelets; nor did the bacteria prevent ristocetin-induced platelet agglutination or vWF binding. The aggregation response was not related to plasma vWF activity levels in normal subjects or in patients with von Willebrand's disease. The platelet response to S. sanguis therefore resembles true aggregation, requiring the cyclo-oxygenase pathway and the presence of glycoprotein IIb/IIIa. The mechanism also involves glycoprotein Ib, but not apparently through irreversible binding of vWF.

Topics: Agglutination; Aspirin; Blood Platelets; Cells, Cultured; Endocarditis, Bacterial; Humans; Platelet Aggregation; Serotonin; Streptococcal Infections; Streptococcus sanguis; Thrombasthenia; Thromboxane B2; von Willebrand Diseases

An autosomal recessive thrombopathy in pigs is described and characterized functionally, morphologically and biochemically. The affected pigs have a severe bleeding diathesis and a markedly prolonged bleeding time but normal plasma and platelet von Willebrand factor (vWF) levels. Electron micrographs and fluorescence microscopy with mepacrine reveal reduced numbers of dense granules in platelets as compared to normals. This thrombopathy is a pure delta storage pool disease (SPD), as evidenced: a) biochemically by platelet serotonin content and metabolism and by comparative ATP/ADP content and secretion; b) functionally by reduced aggregability to low concentrations of convulxin and collagen but normal aggregability to other agents and normal synthesis of thromboxane B2. The affection was first discovered in a colony of von Willebrand's disease (vWD) pigs, but is biologically and genetically distinct. It is possible to completely separate the SPD from the vWD, although originally animals could be affected by both vWD and SPD. Normal plasma and platelet alpha granule content of vWF are found in diseased animals. An intermediate disorder is also detected in animals not severely affected, which may represent the heterozygous state.

Topics: Acetylserotonin O-Methyltransferase; Adenine Nucleotides; Animals; Arylamine N-Acetyltransferase; Blood Platelets; Cytoplasmic Granules; Genes, Recessive; Microscopy, Electron; Platelet Aggregation; Platelet Storage Pool Deficiency; Serotonin; Swine; Swine Diseases; Thromboxane B2; von Willebrand Diseases; von Willebrand Factor

The production of thomboxane B2, the primary metabolite of thromboxane A2, and 6-keto prostaglandin F1 alpha, the primary metabolite of prostacyclin, were measured in response to a standardized vascular injury, the bleeding time, in patients with von Willebrand's disease and in patients with platelet function defects. Compared to controls, thromboxane B2 levels in bleeding time blood were significantly lower in subjects with von Willebrand's disease. In patients with platelet function defects associated with a deficient response to thromboxane A2, thromboxane B2 production in bleeding time blood was similar to controls. In subjects with other platelet function defects, thromboxane production was significantly lower than normal. 6-keto PGF1 alpha production in bleeding time blood was not significantly different in patients compared to controls. The results suggest that bleeding time thromboxane production is influenced by the extent of platelet-vessel interaction.

Topics: 6-Ketoprostaglandin F1 alpha; Adolescent; Adult; Aged; Blood Platelet Disorders; Blood Platelets; Blood Vessels; Child; Child, Preschool; Humans; Middle Aged; Platelet Aggregation; Thromboxane B2; Thromboxanes; von Willebrand Diseases

The present studies demonstrate that platelets from patients with platelet-type von Willebrand disease show specific and saturable binding of asialo von Willebrand factor (AS-vWF) under conditions where such binding is not observed with normal platelets. Although specific binding of 125I-AS-vWF to formalin-fixed normal platelets could not be demonstrated, specific binding to fixed patient platelets was seen with an apparent Kd of 1.3 micrograms/mL and specific maximally bound ligand of 0.40 micrograms/10(8) platelets. Preincubation of patient platelets with the antiglycoprotein Ib (anti-GPIb) monoclonal antibody AS-2 reduced total binding close to the level of computer-estimated nonspecific binding. In contrast, binding was not reduced by preincubation with anti-GPIIb/IIIa monoclonal antibody or with 5 mmol/L EDTA. Under stirring conditions, the binding of AS-vWF to fixed patient platelets was accompanied by a strong agglutination response. AS-vWF-induced agglutination was similarly observed in patient but not normal platelet-rich plasma (PRP) in the presence of 5 mmol/L EDTA. In the absence of EDTA, AS-vWF produced a full aggregation response in patient PRP at concentrations as low as 0.1 microgram/mL in contrast to the 2 to 20 micrograms/mL required by normal PRP. Both thromboxane B2 formation and adenosine triphosphate secretion showed an AS-vWF concentration dependence paralleling the aggregation responses. These studies show that a major difference in the platelets from patients with platelet-type von Willebrand disease is the presence of an exposed, high-affinity binding site associated with GPIb that recognizes AS-vWF.

Topics: Adenosine Triphosphate; Asialoglycoproteins; Binding Sites; Blood Platelets; Edetic Acid; Humans; Platelet Aggregation; Ristocetin; Thromboxane B2; von Willebrand Diseases; von Willebrand Factor

Desamino-D-arginine vasopressin (DDAVP) is known to stimulate factor VIII (FVIII) and plasminogen activator release from endothelial cells, and has been shown to stimulate prostacyclin (PGI2) production in normal and haemophilic subjects. In von Willebrand's disease (vWd) some patients have a dissociate response with regard to FVIII and plasminogen activator. The aim of our study was to compare the PGI2, FVIII and plasminogen activator response to DDAVP infusion in vWd with the response to DDAVP in normal and haemophilic subjects. PGI2 metabolites thromboxane B2 (TxB2), factor VIII coagulant activity, factor VIII-related antigen and plasminogen activator were measured before and after DDAVP infusion. There was a significant increase in PGI2 metabolites, factor VIII-related antigen and plasminogen activator in all groups following DDAVP, but no effect on TxB2 was found, and there was no evidence of any dissociate response to DDAVP in any of the groups. Basal levels of PGI2 metabolites, however, were significantly lower in vWd as compared to normal and haemophilic subjects. Post-DDAVP levels of PGI2 metabolites were also significantly lower in vWd as compared with normal subjects. This may be due to a reduced stimulus to PGI2 production in vWd secondary to defective platelet adhesion.

Topics: Antigens; Deamino Arginine Vasopressin; Endothelium; Epoprostenol; Factor VIII; Female; Hemophilia A; Humans; Male; Plasminogen Activators; Thromboxane B2; von Willebrand Diseases; von Willebrand Factor