摘要:

The effects of various concentrations of platelets and plasma onin vitrot-PA-induced fibrinolysis were investigated. At t-PA levels between 30 and 70 ng/ml, fibrinolysis proceeded faster in platelet-rich plasma (PRP) than in platelet-poor plasma (PPP). When PRP was serially diluted with PPP and the rate of fibrinolysis compared to PPP, higher platelet counts (up to 300 ± 109/1) were associated with increased enhancement of lysis. However, lysis was inhibited when platelets were added to plasma diluted with buffer. Thus, platelets enhance fibrinolysis in undiluted plasma but inhibit lysis in diluted plasma. This is probably because platelets provide a catalytic surface for fibrinolysis but also release inhibitors of fibrinolysis. In undiluted plasma, there would be sufficient fibrinogen and plasminogen to overcome the effect of the platelet inhibitors, but in diluted systems, the inhibitors would predominate, retarding fibrinolysis.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

To study the effect of the severe loss of hepatic synthetic function on the inhibitors of coagulation we have measured protein S (total and free), protein C, heparin cofactor II and antithrombin III in 30 patients with fulminant hepatic failure. The results showed severe reduction in all inhibitor levels with mean (± SE) values of: protein S, 0.26 ± 0.03 U/ml; protein C, 0.26 ± 0.03 U/ml; heparin cofactor II, 0.12 ± 0.02 U/ml and antithrombin III, 0.21 ± 0.02 U/ml. Heparin cofactor II was significantly lower than the other inhibitors (P< 0.01). Although the reduction in free protein S was significant in fulminant hepatic failure as compared to normal subjects (0.40 ± 0.05 U/ml compared to 1.02 ±0.08 U/ml,P< 0.001), the ratio of free to total protein S was significantly increased (0.67 ± 0.02 compared to 0.40 ± 0.04,P< 0.01). Prothrombin time (INR) was significantly inversely correlated with total protein S (r= - 0.56,P< 0.001) and free protein S (r= −0.48,P< 0.01), but not with the ratio of free to total protein S. No significant correlation between the different coagulation inhibitors and other measures of hepatic function could be detected. Although the loss of hepatic synthetic function appears to be the major cause of the loss of coagulation inhibitors, other effects such as increased consumption and rate of clearance may play a role. The balance of these will be reflected in the circulating levels of the coagulation inhibitors.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Lipoprotein(a) (Lp(a)) has been established as an important independent risk factor for the development of cardiovascular disease. Apolipoprotein(a), together with apo B-100 the apolipoprotein of Lp(a), is homologeous to plasminogen but lacks fibrinolytic capacity and appeared to interfere with fibrinolysis inin vitroandex vivoexperiments. We determined the correlations between Lp(a) and other blood lipids (serum cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides), coagulation parameters (fibrinogen, factor VII, factor VIII:C fibrin monomers, thrombin-antithrombin III) and fibrinolysis parameters (tissue plasminogen activator antigen, plasminogen activator inhibitor-1 and D-dimer) in 54 patients with essential hypertension, in 65 non-insulin-dependent diabetic patients and in 116 insulin-regulated diabetic patients. Signs of activated coagulation and increased reactive fibrinolysis were found in all three patient groups. In the hypertensive patients, Lp(a) was significantly correlated with LDL-cholesterol (r=0.25,P= 0.04) and triglycerides (r= −0.30,P= 0.03), while in insulin-regulated diabetics, Lp(a) was also correlated with LDL-cholesterol (r=0.20,P= 0.03). In the hypertensive patients and both diabetic groups there was no correlation of Lp(a) with coagulation or fibrinolysis parameters. These data show that Lp(a) concentrations are not related to coagulation or fibrinolysis parameters in hypertensive or diabetic patients and confirm the presence of an activated coagulation system in these patient groups.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The inactivation of factor Va by the natural anticoagulant, activated protein C (APC) is subject to a number of regulatory mechanisms. This report examines the efficacy of APC in plasma and evaluates the role of the APC cofactor protein S in this milieu. The ability of protein S to enhance the anticoagulant effects of activated protein C was demonstrated using a factor Xa recalcification time of Al(OH)3adsorbed plasma. At a set concentration of APC, increasing concentrations of protein S resulted in a linear and saturable potentiation of the activity of APC. This result was not reflected in a purified component assay, where the extent of factor Va inactivation by APC was only marginally augmented by protein S. The efficacy of the cofactor was not affected by variations in the concentration of factor Va. Similarly, increasing the protein S:APC molar ratio to 200:1 resulted in only a trivial enhancement of APC activity. To directly examine the proteolysis of factor Va by APC in plasma, a novel assay system containing Al(OH), adsorbed, factor V deficient plasma supplemented with purified human factor Va was developed. The addition of APC in varying concentrations to this system consistently yielded factor Va inactivation rates inferior to those seen in a purified component assay. This finding is consistent with the presence of APC inhibitory activity in plasma. When protein S was added to the plasma system, factor Va inactivation by APC was restored to a similar level to that observed in the purified system. A dose-dependent reduction in APC activity was observed when increasing concentrations of Al(OH), adsorbed factor V deficient plasma was added to the purified system. This diminution of APC activity was mirrored by a progressive increase in protein S activity when the cofactor was included in the assay. This finding suggests that protein S activity is primarily mediated through interference with the inhibition of APC by an as yet uncharacterized plasma factor.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Whereas tissue factor, a high-affinity cell-surface receptor and essential cofactor for the serine protease factor VII is constitutively present in certain tissues such as epithelial tissue, brain and placenta, it is not normally expressed by cells within the vasculature. However, the stimulation of monocytes and endothelial cells by a variety of inflammatory and immunological reactions results in the induction of cell surface tissue factor (TF) expression. TF is also expressed on tumour cells, and may play a role in tumour growth and metastasis formation. To examine the role of TF in these processes we developed monoclonal antibodies to human tissue factor apoprotein. The antibodies were characterized by neutralization of the procoagulant activity and by immunoblotting. With two of these monoclonal antibodies a sandwich ELISA was developed for the rapid quantitation of TF. The sensitivity of the assay permits extensive studies involving the modulation of TF expression on small numbers of cells. The results are comparable to the functional clotting assay as evaluated with unpurified TF and with the tumour cell line MCF-7. For certain applications, monitoring of cellular TF expression by ELISA using anti-TF monoclonal antibodies is preferable because it is not influenced by other coagulation factors or by inhibitors of procoagulant activity on the cells.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The basal platelet level of reactive oxygen species and their enhancement following stimulation by different agonists were determined in a selected group of patients with essential thrombocythaemia (ET). Activated platelets had lower levels of superoxide anion and higher intracellular concentrations of hydrogen peroxide than controls. Higher levels of lipid peroxidation induced byN-ethylmaleimide were also observed. Measurement of the most important enzymes generating and scavenging these reactive oxygen species revealed increased specific activities of NADPH-cytochrome c reductase and superoxide dismutase and a decrease in platelet catalase activity in patients with ET. Since an abnormal production of oxygen radicals seems to be implicated in various pathological conditions and ageing processes, the increased amount of hydrogen peroxide found in platelets of patients could be involved in some of the platelet alterations described in ET.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Although heparin is currently used in concomitance with thrombolytic agents to improve their efficacy, its effect on fibrinolysis is controversial. We have evaluated the sensitivity to t-PA-induced lysis of clots prepared from plasma preincubatedin vitrowith thera-peutic concentrations of heparin. The extent of t-PA-induced lysis was significantly increased by preincubation of plasma with 0.5 and 1.0 U/ml heparin. The concentration of t-PA required to give similar lysis rates were reduced by up to five times after adding 1.0 U/ml heparin to plasma prior to clot formation. Heparin added to the t-PA-containing medium after clot formation did not exert any signifi-cant effect. The effect of heparin was not mediated by the inhibition of thrombin as preincubation of plasma with hirudin did not modify clot sensitivity to t-PA. We also found that heparin significantly modified fibrin assembly and clot structure as assessed by a turbidimetric assay. Pre-incubation of fibrinogen with heparin caused an increase in the speed of fibrin fibre polymerization and in the turbidity of the final fibrin gel; changes known to be associated with the formation of thicker fibrin fibres. Thus the effect of heparin on clot sensitivity to lysis appears to be due to an increased permeability of these clots to fibrinolytic components. This may contribute to the antithrombotic activity and to the haemorrhagic risk of heparin. These findings could be particularly important for clinical thrombolysis. Our data suggest that the concomitant administration of heparin with thrombolytic agents, as well as inhibiting the accretion of new fibrin on the lysing thrombi, could also enhance the lysability of the fibrin eventually accreted on the thrombi.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Commercial partial thromboplastin reagents markedly differ in their sensitivity to f actor deficiency, heparin, or the lupus anticoagulant. These differences may be partly due to the variable phospholipid content of different commercially available reagents. For over 15 years, we have routinely used a partial thromboplastin prepared from human brain. In the past four years, we have been using a similarly prepared bovine partial thromboplastin reagent. This report describes the preparation of our partial thromboplastin reagent, as well as an analysis of the phospholipid composition of both the human and bovine thromboplastin reagents. Four separate brain preparations produced consistent percentages of the anionic phospholipids, phosphatidylserine, and phosphatidylinositol. The bovine reagent was also compared with commercial partial thromboplastin reagents in the detection of coagulation factor deficiency, heparin, and the lupus anticoagulant.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The plasma protein S (PS) System was studied in 120 HIV seropositive patients (CDC classification: group II:n= 35; group III:n= 6; groups IVA, IVC2 or IVE,n= 38; groups IVB, IVC1 or IVD,n= 41). Total PS antigen and C4b-binding protein (C4b-BP) values were not significantly different from contro) values. Free protein S levels assessed by an immunological method in the supernatant of PEG-precipitated plasma samples (PEG-fPS) were below the normal limit in 85 patients, lower values being found in patients with advanced HIV disease. No correlation was found between PEG-fPS levels and C4b-BP or total PS levels. At least 25 patients had a low functional PS value. Low functional levels of PS were found in each clinical group although there was no difference in the distribution of functional PS values among groups. Crossed immuno-electrophoresis showed an abnormal distribution of PS in some patients, but failed to confirm the marked decrease of free PS in patients with very low PEG-fPS. An impairment of the protein S System is observed in HIV-infected patients. However, the discrepancies found in some patients among the results of the various PS-related assays should lead to a cautious interpretation concerning the incidence of PS deficiency in HIV-infected patients.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

A reproducible and sensitive one-step enzyme immunoassay (EIA) was developed to determine total tissue-type plasminogen activator (t-PA) antigen in plasma. The EIA comprises two monoclonal catching antibodies and a polydonal (goat) tagging antibody conjugated with horseradish peroxidase. There is an equal reactivity towards the several physiological t-PA forms, i.e., single-chain t-PA two-chain t-PA and t-PA in complex with its naturally occurring inhibitor plasminogen activator inhibitor-type 1 (t-PA/PAI-1 complex). Additionally, the EIA does not discriminate between human melanoma t-PA and recombinant t-PA (Activase). The assay has a lower detection limit of approximately 0.5 ng t-PA per ml plasma, with a time-to-resuU of only 3.5 h.

ISSN:0957-5235    

出版商:OVID    

年代:1992

数据来源: OVID