thromboxane-a2 and Blood-Coagulation-Disorders

Topics: Adolescent; Adult; Aspirin; Blood Coagulation Disorders; Child; Dipyridamole; Epoprostenol; Female; Humans; Immunologic Deficiency Syndromes; Male; Plasmapheresis; Purpura, Thrombotic Thrombocytopenic; Thromboxane A2

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

Topics: Animals; Arachidonic Acids; Blood Coagulation Disorders; Fibrinolysis; Hemostasis; Humans; Mice; Neoplasm Metastasis; Neoplasms; Neoplasms, Experimental; Neoplastic Cells, Circulating; Platelet Aggregation; Thrombocytopenia; Thromboxane A2

Twenty patients with prostatic carcinoma were randomized to therapy with either oestrogens (n = 10) or orchidectomy (n = 10). Activators and inhibitors of coagulation were studied before treatment, 1.5 months and 6 months after the start of treatment. We found that the patients in the oestrogen group had already increased their factor VII level after 1.5 months (P less than 0.001) and this increased level persisted after 6 months. Factor X tended to increase after 1.5 months and this increase reached significance after 6 months (P less than 0.01). In the orchidectomy groups there was a significant increase in factor X at 6 months (P less than 0.01) and, in addition, antithrombin III (AT III) was increased at this time. Furthermore, there was a parallelism between the increase in factor VII and electrocardiographic evidence of increased coronary insufficiency (r = 0.60; P less than 0.025; n = 15). We found a significant increase of thromboxane as evidenced by the major urinary metabolite 2,3-dinorthromboxane B2 in the oestrogen group as compared to the orchidectomy group. In summary, patients with prostatic cancer during long-term oestrogen treatment were found to have increased levels of factor VII, factor VIII:C and fibrinogen. In addition these patients showed increased formation of thromboxane. The changes imply a hypercoaguable state and platelet activation. No such signs were found after orchidectomy. The findings in the oestrogen group might explain the continuously increased risk of cardiovascular complications during long-term oestrogen therapy.

Topics: Aged; Antigens; Blood Coagulation Disorders; Data Interpretation, Statistical; Epoprostenol; Estradiol; Ethinyl Estradiol; Exercise Test; Factor VII; Fibrinogen; Fibrinolysis; Humans; Male; Orchiectomy; Prospective Studies; Prostatic Neoplasms; Random Allocation; Thromboxane A2; Time Factors

Thromboxane A2 (TXA2), synthesized in platelets, is a powerful aggregating agent and vasoconstrictor. To induce platelet aggregation, the platelets' enzyme, prostaglandin endoperoxide H synthase-1 (PGHS-1), first converts arachidonic acid (AA) into prostaglandin H2 (PGH2). PGH2 is then converted by the enzyme thromboxane synthase into TXA2. Finally, TXA2 is secreted and can activate the TXA2 receptor on the platelet surface. The importance of TXA2 in haemostasis has been demonstrated by the presence of a bleeding tendency in patients showing an inherited defect in the TXA2 production pathway. We studied an 18-year-old woman with a lifelong bleeding disorder, moderate thrombocytopenia (55-71 x 109/l) and a prolonged bleeding time (12.5 min). Her platelets aggregated in the presence of both PGH2 and a stable TXA2 analogue, but did not aggregate in the presence of AA. The activity of PGHS-1 in platelets, measured using thin-layer chromatography and radioactive counting of TXA2 formation from [14C]-AA, was reduced to 13% of the activity measured in control subjects. PGHS-1 protein levels, measured using Western blot analysis, were also markedly reduced to 10% of control values. Such levels of PGHS-1 enzyme were too low to sustain platelet aggregation in the patient, even if the enzyme was active. The PGHS-1 protein level was also reduced in the patient's immortalized B lymphocytes, suggesting a systemic expression defect. Northern blot analysis was then carried out with poly (A)+ RNA extracted from the patient's immortalized B lymphocytes. PGHS-1 mRNA was detected as a 2.8-kb band in both the patient and control. The intensity of the band representing the patient's PGHS-1 mRNA was similar to that of the control subject. The Northern blot result suggests a normal transcriptional rate of the PGHS-1 gene for the patient. Therefore, the defect responsible for the reduced levels of PGHS-1 protein is probably post-transcriptional.

Topics: Adult; Arachidonic Acid; Autoradiography; B-Lymphocytes; Blood Coagulation Disorders; Blood Platelets; Blotting, Northern; Blotting, Western; Case-Control Studies; Cell Line; Female; Humans; Male; Middle Aged; Platelet Aggregation; Prostaglandin-Endoperoxide Synthases; RNA, Messenger; Thromboxane A2; Thromboxane B2

Thromboxane A2 (TXA2) is a labile metabolite of arachidonic acid that has potent biological effects. Its actions are mediated by G protein-coupled thromboxane-prostanoid (TP) receptors. TP receptors have been implicated in the pathogenesis of cardiovascular diseases. To investigate the physiological functions of TP receptors, we generated TP receptor-deficient mice by gene targeting. Tp-/- animals reproduce and survive in expected numbers, and their major organ systems are normal. Thromboxane agonist binding cannot be detected in tissues from Tp-/- mice. Bleeding times are prolonged in Tp-/- mice and their platelets do not aggregate after exposure to TXA2 agonists. Aggregation responses after collagen stimulation are also delayed, although ADP-stimulated aggregation is normal. Infusion of the TP receptor agonist U-46619 causes transient increases in blood pressure followed by cardiovascular collapse in wild-type mice, but U-46619 caused no hemodynamic effect in Tp-/- mice. Tp-/- mice are also resistant to arachidonic acid-induced shock, although arachidonic acid signifi-cantly reduced blood pressure in Tp-/- mice. In summary, Tp-/- mice have a mild bleeding disorder and altered vascular responses to TXA2 and arachidonic acid. Our studies suggest that most of the recognized functions of TXA2 are mediated by the single known Tp gene locus.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine Diphosphate; Animals; Arachidonic Acid; Bleeding Time; Blood Coagulation Disorders; Collagen; Female; Hemodynamics; Male; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Mice, Knockout; Platelet Aggregation; Platelet Aggregation Inhibitors; Receptors, Thromboxane; Shock; Thromboxane A2

Defective platelet prostaglandin H synthase (PGHS) activity has been recognized as a cause of bleeding disorders, but the defect has not been characterized. We evaluated three female patients aged 37, 48 and 55 who presented with a mild bleeding disorder due to platelet dysfunction. None of the patients had underlying diseases or reported use of aspirin or other nonsteroidal anti-inflammatory drugs. Coagulation screening tests and platelet count were normal in each patient. Platelet aggregation in response to adenosine diphosphate (ADP), collagen and epinephrine were subnormal, characterized by an abnormal second-wave aggregation and propensity for disaggregation. Arachidonate-induced platelet aggregation was defective, whereas PGH2-induced aggregation was normal. Platelet thromboxane A2 (TXA2) production in response to arachidonic acid was reduced in all three patients, i.e. 11.7, 4.6 and 4.4 ng TXB2/3 x 10(8) plt respectively (normal range was 49-81 ng/3 x 10(8) plt), whereas they were normal in response to exogenous PGH2, i.e. 71.4, 56.6 and 48.9 ng/3 x 10(8) respectively (normal range 49-85 ng/3 x 10(8) plt). These results are consistent with a deficiency of platelet PGHS activity. The level of the constitutive platelet PGHS-1 and TXA2 synthase (TXAS) proteins were determined on platelet microsomal fractions by Western blot analysis using affinity-purified polyclonal antibodies highly specific for human PGHS-1 and TXAS, respectively. In two patients the 70 kD PGHS-1 protein was undetectable, whereas it was normal in the third patient. The 60 kD TXAS band was normal in all three patients. These findings indicate that human platelet PGHS-1 deficiency is due to two types of enzyme defects: type 1 defect is manifested by an undetectable PGHS-1 protein in platelets whereas the type 2 defect is manifested by a normal quantity of PGHS-1 protein which has an impaired catalytic activity.

Topics: Adult; Arachidonic Acid; Blood Coagulation Disorders; Blotting, Western; Female; Humans; Middle Aged; Platelet Aggregation; Prostaglandin H2; Prostaglandin-Endoperoxide Synthases; Prostaglandins H; Thromboxane A2; Thromboxane-A Synthase

A patient with a mild bleeding disorder whose platelets responded defectively to thromboxane A2 (TXA2) was identified, and the mechanism of this dysfunction was analyzed. The platelets were defective in shape change, aggregation, and release reaction in response to synthetic TXA2 mimetic (STA2). When the platelet TXA2 receptor was examined with both a 125I-labeled derivative of a TXA2 receptor antagonist ([125I]-PTAOH) and [3H]-labeled TXA2 agonist ([3H]U-46619), the equilibrium dissociation rate constants (kd) and the maximal concentrations of binding sites (Bmax) of the platelets to both ligands were within normal ranges, suggesting that the binding capacity of their TXA2 receptor was normal. STA2 could not induce IP3 formation and intracellular Ca2+ mobilization, whereas these responses to thrombin were within normal ranges. GTPase activity was also decreased when the patient's platelet membrane was challenged with STA2. On the other hand, lysophosphatidylinositol formation, which is a direct indicator of phospholipase A2 (PLA2) activation, was found to be normal when the [3H]-inositol-labeled platelets were challenged with STA2. Thromboxane B2 (TXB2) was also produced in response to STA2. These results suggested that the abnormality in these platelets was impaired coupling between TXA2 receptor and phospholipase C (PLC) activation. Furthermore, it is also suggested that the activation of PLA2 and PLC are separable events in thromboxane-induced platelet activation.

Topics: Adult; Blood Coagulation Disorders; Blood Platelets; Calcium; Enzyme Activation; Female; GTP Phosphohydrolases; Humans; Inositol 1,4,5-Trisphosphate; Male; Middle Aged; Phospholipases A; Phospholipases A2; Platelet Aggregation; Receptors, Thromboxane; Signal Transduction; Thrombin; Thromboxane A2; Type C Phospholipases

The effect of STA2, thrombin and NaF on PI metabolism and Ca mobilization was investigated in patients with three kinds of platelet dysfunction, one each with platelet cyclo-oxygenase deficiency (A), defective aggregation to A23187 (B) and defective aggregation to STA2 (C). These responses were normal in patient (A), suggesting cyclooxygenase activity did not affect PI metabolism and Ca mobilization. PI metabolism was also normal in (B), although Ca mobilization in response to A23187 was delayed and that in response to thrombin was defective in the presence of extracellular Ca2+. This suggests that the patient's platelets have a defective IP3-induced Ca mobilization pathway. STA2 selectively failed to induce IP3 formation and Ca mobilization in (C), although 3H-labelled thromboxane ligand (3H-U46619) bound to the patient's platelets normally. It was suggested that the patient's platelets have a defect in postreceptor signal transduction, especially thromboxane receptor-mediated PLC activation pathway.

Topics: Blood Coagulation Disorders; Blood Platelets; Calcimycin; Calcium; Humans; Phosphatidylinositols; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin-Endoperoxide Synthases; Receptors, Prostaglandin; Receptors, Thromboxane; Signal Transduction; Sodium Fluoride; Thrombin; Thromboxane A2; Type C Phospholipases

Topics: Animals; Aspirin; Blood Coagulation Disorders; Cyclooxygenase Inhibitors; Dogs; Fatty Acids, Monounsaturated; Humans; Methacrylates; Phospholipases; Receptors, Prostaglandin; Receptors, Thromboxane; Renal Dialysis; Sulfinpyrazone; Thromboxane A2; Thromboxane-A Synthase

Platelet aggregation, secretion, and thromboxane formation induced by various agonists, including arachidonate, prostaglandin-G2 (PGG2), and thromboxane-A2 (TxA2), were examined in a patient with a bleeding disorder who was previously reported to have a TxA2-related defect. Aggregation and 14C-5HT secretion were decreased, and no TxB2 formation occurred in response to adenosine diphosphate (ADP), epinephrine, or collagen. Arachidonate-induced aggregation and TxB2 formation, and PGG2-induced aggregation (but not TxB2 formation) were impaired at low agonist concentrations. The patient's platelets did not aggregate in response to TxA2 generated from arachidonate in normal platelets, but were capable of synthesizing TxA2 from both arachidonate and PGG2. In addition, aggregation and secretion induced by low concentrations of the ionophore A23187 were impaired in platelet-rich plasma (PRP) and in gel-filtered platelets in the absence of extracellular calcium; these responses became normal at higher A23187 concentrations or, in GFP, at low A23187 concentrations in the presence of exogenous calcium. These findings indicate that the TxA2 defect in this patient does not result from a thromboxane synthetase deficiency, but may be due to impaired mobilization of platelet calcium, and thus are consistent with the possibility that TxA2 may act as a calcium ionophore.

Topics: Arachidonic Acids; Blood Coagulation Disorders; Blood Platelets; Calcium; Humans; Ionophores; Platelet Aggregation; Prostaglandins G; Serotonin; Thromboxane A2; Thromboxanes