bluuebunny/crossref_metadata_2025_split huggingface dataset:
Significance of Platelet β-Adrenoceptors for Platelet Responses In Vivo and In Vitro
Authors: Larsson P T , Wallén N H , Martinsson A , Egberg N , Hjemdahl P 
Published: July 2018

SummaryThe significance of platelet β-adrenoceptors for platelet responses to adrenergic stimuli in vivo and in vitro was studied in healthy volunteers. Low dose infusion of the β-adrenoceptor agonist isoprenaline decreased platelet aggregability in vivo as measured by ex vivo filtragometry. Infusion of adrenaline, a mixed α- and β-adrenoceptor agonist, increased platelet aggregability in vivo markedly, as measured by ex vivo filtragometry and plasma β-thromboglobulin levels. Adrenaline levels were 3–4 nM in venous plasma during infusion. Both adrenaline and high dose isoprenaline elevated plasma von Willebrand factor antigen levels β-Blockade by propranolol did not alter our measures of platelet aggregability at rest or during adrenaline infusions, but inhibited adrenaline-induced increases in vWf:ag. In a model using filtragometry to assess platelet aggregability in whole blood in vitro, propranolol enhanced the proaggregatory actions of 5 nM, but not of 10 nM adrenaline. The present data suggest that β-adrenoceptor stimulation can inhibit platelet function in vivo but that effects of adrenaline at high physiological concentrations are dominated by an α-adrenoceptor mediated proaggregatory action.
Biochemical and Ultrastructural Studies Suggest that the Effects of Thapsigargin on Human Platelets Are Mediated by Changes in Intracellular Calcium but not by Intracellular Histamine
Authors: Saxena Satya P , McNicol Archibald , Becker Allan B , Brandes Lorne J , Thastrup Ole , Gerrard Jon M 
Published: July 2018

SummaryThe involvement of intracellular histamine in thapsigargin (Tg)-induced platelet aggregation was studied. Platelet aggregation induced by 0.25 and 0.5 µM Tg was not accompained by a rise in intracellular histamine but a significant (p <0.01) increase in the level of intracellular histamine was observed at 1 µM Tg. Preincubation of platelets with inhibitors of histamine metabolizing enzymes had little effect on intracellular histamine levels in platelets stimulated by 0.5 µM Tg. In addition, the inhibitors of histidine decarboxylase (HDC), α-methyl histidine (α-MH) and α-fluoromethyl histidine (α-FMH) failed to inhibit Tg-induced aggregation. The intracellular histamine receptor antagonist, N,N-diethyl-2-[4-(phenylmethyl)phenoxy] ethanamine. HC1 (DPPE), inhibited Tg-induced aggregation but with IC50 values dependent on the concentration of agonist used. The inhibitory effects of DPPE on Tg-induced aggregation were not reversed by the addition of histamine to saponin-permeabilized platelets suggesting non-histamine mediated effects of DPPE on Tg-induced aggregation. Tg stimulated an increase in the cytosolic free calcium concentration which was unaffected by DPPE indicating that the effects of DPPE are also not due to the inhibition of mobilization of cytosolic calcium. The ultrastructural studies suggest that the major Tg-induced changes (pseudopod formation and granule centralization) are consistent with a primary role for Tg to mobilize calcium; DPPE had very little effect on these ultrastructural changes. The results indicate that the effects of Tg on human platelets are mediated by an increase in cytosolic calcium but not by intracellular histamine.
Antibodies to Thrombomodulin Induce Receptor-Mediated Endocytosis in Human Saphenous Vein Endothelial Cells
Authors: Brisson Christine , Archipoff Gisèle , Hartmann Marie-Louise , Hanau Daniel , Beretz Alain , Freyssinet Jean-Marie , Cazenave Jean-Pierre 
Published: July 2018

SummaryThe membrane glycoprotein thrombomodulin (TM) is an essential endothelial cell (EC) cofactor, which forms a 1:1 stoichiometric complex with thrombin. Binding of thrombin to the high affinity TM receptor transforms its procoagulant activity into an anticoagulant potential, by activating protein C. The fate of TM in the presence of thrombin is still unclear: some authors claim that the thrombin-TM complex is internalized in EC, while others find this complex to be stable for at least 2 h at 37° C on the EC surface. In the present study, we investigated the interactions of thrombin and Fab-fragments of anti-TM antibodies, coupled to 5 or 15 nm gold particles with saphenous vein endothelial cells. Our results demonstrate that TM can be observed both on the plasma membrane and in coated structures only in the presence of anti-TM antibodies. Addition of thrombin decreased the extent of this labeling, while in double labeling experiments, where cells were incubated with 5 nm gold coupled thrombin and 15 nm gold coupled Fab fragments of anti-TM antibodies, thrombin was cointernalized only when anti-TM antibodies were present. These results show that thrombin-TM complex is not significantly internalized in EC. The internalization of this complex induced by anti-TM antibodies could play an important role in the thrombotic complications induced by anti-EC autoantibodies.
Pharmacokinetics and Pharmacodynamics of Saruplase, an Unglycosylated Single-chain Urokinase-type Plasminogen Activator, in Patients with Acute Myocardial Infarction
Authors: Koster Rudolph W , Cohen Adam F , Hopkins Gwyn R , Beier Horst , Gunzler Wolfgang A , van der Wouw Poll A 
Published: July 2018

SummaryWe examined in patients with acute myocardial infarction (AMI) the pharmacokinetics of saruplase, an unglycosylated, single chain, urokinase-type plasminogen activator (rscu-PA) by measuring urokinase-type plasminogen activator (u-PA) antigen and total u-PA activity, its conversion to active two-chain urokinase-type plasminogen activator (tcu-PA) and evaluated its effect on haemostatic parameters.Twelve patients were studied during and after administration of 20 mg bolus plus 60 mg continuous 1 h i.v. infusion of saruplase. For u-PA antigen and total u-PA activity (expressed as protein equivalents), where 234 U corresponds to 1 μg, respectively, steady state plasma concentrations were 2.75 ± 8.3 and 2.50 ± 7.0 μg/ml (mean ± standard deviation) and were reached within 20min, t1/2M was 9.1 ± 1.8 and 7.8 ± 1.3 min, t1/2λ2 1.2 ± 0.2 and 1.9 ± 0.5 h, and the total clearance was 393 ±110 and 427 ± 113 ml/min. Inactivation of saruplase in plasma was negligible.After 15 min, tcu-PA was detected in plasma. From the ratio of the areas under the curve of tcu-PA and total u-PA activities it was calculated that 28 ± 9.3% of the saruplase dose is converted into active tcu-PA. Systemic plasminaemia occurs as shown by a decrease in α2-antiplas-min and fibrinogen and an increase in fibrinogen degradation products. Thrombin-antithrombin complex formation indicated activation of the clotting system.Saruplase is eliminated rapidly from plasma in AMI patients. A variable, but significant proportion of saruplase is converted into active tcu-PA. At the end of the infusion tcu-PA accounted for 55% of total u-PA activity. Systemic plasmin generation and activation of the clotting system occur during saruplase treatment for AMI.
Thrombin-stimulated Human Platelets Express Molecular Forms of α-Granule Factor V (FV), which Differ from FVa
Authors: Wyshock Edward G , Stewart Gwendolyn J , Colman Robert W 
Published: July 2018

SummaryBinding of 125I-Fab fragments of chain-specific antibodies indicate that both heavy and light chains of a-granule factor Va (FVa) were externalized on the platelet membrane after stimulation with thrombin. Using a Mab against the activation peptide of factor V (FV), the epitope appears on the stimulated platelet surface. Half as much light chain and heavy chain (FVa) was expressed compared to the activation peptide, suggesting that expression of α-granule FV occurs after thrombin stimulation. Using an ELISA, we find that 32% of a-granule FV was released and 68% is retained in the platelet pellet. Immunoblots of platelets indicate that FV exists in 200 kDa und 150 kDa forms, representing incomplete cleavage, while the releasate demonstrates a more complete cleavage by proteases. We conclude that expression of α-granule FV is quantitatively greater than that released and exists in molecular forms which cannot be completely explained by the binding of FVa.
Thrombin Generation during Cardiac Surgery: Is Heparin the Ideal Anticoagulant?
Authors: Brister S J , Ofosu F A , Buchanan M R 
Published: July 2018

SummaryBlood samples were collected from 43 patients undergoing elective cardiac surgery to determine the extent of thrombin generation and inhibition in patients when receiving heparin while undergoing cardiopulmonary bypass (CPB). Plasma prothrombin fragment F1 + 2 and thrombin-antithrombin III (TAT) levels were measured as markers of thrombin generation and inhibition, respectively. Both F1 + 2 and TAT levels increased significantly during the course of CPB despite the heparin causing significant systemic anticoagulation, i.e. the activated coagulation time (ACT) was prolonged to greater than 400 s throughout the entire surgical procedure. The extent of thrombin generation increased with time on CPB but did not differ between patients receiving normothermic and hypothermic cardioplegia during CPB. Furthermore, thrombin generation increased following the neutralization of the heparin with protamine sulphate, and continued to be elevated significantly 24 h post surgery. The observation that high dose heparin did not prevent thrombin generation during CPB, is consistent with previous experimental studies demonstrating that thrombin bound to fibrin or other surfaces (e.g. the CPB conduit) is resistant to antithrombin III/heparin inhibition, and thus able to facilitate further thrombin generation. The observation that thrombin generation continued to be elevated post surgery i.e. 24 h after neutralizing the heparin with protamine sulphate, suggests that the high dose heparin did not inhibit effectively all of the thrombin that had been generated. Thus, CPB patients may be at risk not only of bleeding and other side-effects associated with the acute use of high dose heparin, but may also be at risk of further thrombosis-related events either acutely or chronically.
The Use of Active Centre Acylation to Control the Pharmacokinetic Profile of a Recombinant Chimaeric Plasminogen Activator
Authors: Wilson S , Cronk D W , Dodd I , Esmail A F , Kalindjian S B , McMurdo L , Browne M J , Smith R A G , Robinson J H 
Published: July 2018

SummaryRecombinant hybrid plasminogen activators consisting of the “A” chain of plasminogen linked to the “B” chain of t-PA that are inhibited rapidly by plasma protease inhibitors have recently been described (Robinson et al. Circulation 1992; 86: 548-552). We have now shown that following bolus administration of native hybrid to guinea pigs, fibrinolytic activity was cleared rapidly from the circulation. Active centre acylation appeared to protect the hybrid from inhibition and allowed material to circulate as potentially active species for prolonged periods. Clearance rates of a range of acyl derivatives of the hybrid were 7-35-fold slower than for native hybrid and 20-100-fold slower than for t-PA. Clearance rates were influenced markedly by deacylation rate, such that clearance half-life correlated well with deacylation halflife. We have thus shown that it is feasible to control the pharmacokinetic profile of a recombinant hybrid plasminogen activator over a wide range by selection of an appropriate acyl group for attachment to the active site. Such control is not possible with plasminogen activators that are cleared predominantly by mechanisms other than inhibition.
Inhibitors to Factor VIII in a Family with Mild Hemophilia: Molecular Characterization and Response to Factor VIII and Desmopressin
Authors: Santagostino E , Gringeri A , Tagliavacca L , Mannucci P M 
Published: July 2018

SummaryInhibitor development in patients with mild hemophilia is a rare event. We report the occurrence of a persistent, high-responding inhibitor in two affected members of a mild hemophilia A family and discuss the therapeutic approaches employed in these patients in terms of their efficacy and effect on antibody titer. Desmopressin was an effective option for bleeding management, because endogenous factor VIII released by DDAVP was less immunogenic than exogenous factor VIII replacement, which invariably triggered anamnestic responses. Genetic analysis performed to investigate whether or not a peculiar molecular lesion accounted for this particular phenotype identified a G-A transversion at nucleotide 6507 in exon 23. This missense mutation has been already described in mild hemophilia A, but not in patients with inhibitors.
Some Characteristics of Mouse Platelet Aggregation and a Comparison of the Activity of a Range of Compounds in Mouse and Human Platelet-Rich Plasma in Vitro
Authors: Nunn Barbara 
Published: July 2018

SummaryCollagen-induced platelet aggregation in mouse citrated platelet-rich plasma (PRP) was associated with 5-hydroxytryptamine (5-HT) release and degranulation. Adenosine 5’-diphosphate (ADP) induced monophasic and reversible aggregation with no degranulation. Mouse platelets gave no response to adrenaline but changed shape and sometimes aggregated in response to 5-HT. Both amines potentiated the effect of ADP. The respective potencies of prostaglandin E1, papaverine, VK 774, BL 3459 and adenosine as inhibitors of ADP-induced aggregation were similar in mouse and human PRP. Although ticlopidine had similar activity in the two species, aspirin and flurbiprofen were considerably less potent in mouse than human PRP as inhibitors of collagen-induced aggregation. It is suggested that collagen-induced aggregation of mouse platelets in vitro occurs by a mechanism largely independent of arachidonic acid metabolites.
Studies in Man and Experimental Animals of a Low Molecular Weight Heparin Fraction
Authors: Thomas D P , Merton R E , Lewis W E , Barrowcliffe T W 
Published: July 2018

SummaryIn vitro and in vivo studies were carried out on a commercially prepared low molecular weight heparin fraction. By APTT assay the fraction had a specific activity of half that of unfractionated mucosal heparin, yet retained full potency by anti-Xa assay (both clotting and chromogenic substrate). When administered intravenously to human volunteers, the anti-Xa/APTT ratio remained the same as it was in vitro. However, after subcutaneous injection, the ratio increased and anti-Xa activity could not be fully neutralized ex vivo by PF4. The fraction was as effective as unfractionated heparin in preventing experimental serum-induced thrombosis, suggesting that a heparin fraction with high specific activity by anti-Factor Xa assay compared to APTT activity may be an effective drug for the prophylaxis of venous thrombosis.
Comparison of the Cross-Linking Patterns of Lamprey Fibrinogen and Fibrin by the Action of the Intrinsic Lamprey Factor XIII and Human Factor XIII during the Process of Blood Coagulation
Authors: Murtaugh Patricia A. 
Published: July 2018

SummaryIntrinsic lamprey factor XIII cross-links the γ-chain of lamprey fibrin (50,000 daltons) to the γ-dimer (100,000 daltons). The a-chain (110,000 daltons) is cross-linked very slowly to a-dimer (210,000 daltons) and a-trimer (330,000 daltons). In contrast, human factor XIII, when added in combination with intrinsic lamprey factor XIII, cross-finks the a-chain of lamprey fibrin to a high molecular weight polymer, and any remaining γ-chain is also cross-linked to a polymer. However, the γ-chain that has previously cross-linked to the γ-dimer by the intrinsic lamprey factor XIII remains as a γ-dimer. Factor XIII-free lamprey fibrin cross-links all its subunits (α, β, γ) to high molecular weight polymers when human factor XIII is added. In contrast to human and bovine fibrin where α-chain cross-linking in the process of blood coagulation commences when all of the γ-chain has cross-linked, the lamprey α-chain will begin to cross-link when approximately half of the γ-chain has cross-linked to the γ-dimer.
Evolution of Urokinase-Type Plasminogen Activator (u-PA) and Tissue-Type Plasminogen Activator (t-PA) in Orthotopic Liver Transplantation (OLT)
Authors: Himmelreich G , Dooijewaard G , Breinl P , Bechstein W O , Neuhaus P , Kluft C , Riess H 
Published: July 2018

SummaryIn orthotopic liver transplantation (OLT) hyperfibrinolysis seems to be of causative importance for intra- and postoperative bleeding. Although recently hyperfibrinolysis has been successfully reduced by intraoperative aprotinin treatment, small increases of fibrinolysis still remain during OLT. Originally, tissue-type plasminogen activator (t-PA) was considered to be responsible for the increases, but the efficacy of aprotinin which inhibits besides plasmin also kallikrein and urokinase-type plasminogen activator (u-PA) suggested also a role for the intrinsic and contact system-dependent plasminogen activators. We investigated the role of u-PA. From 29 patients undergoing OLT with intraoperative aprotinin infusion arterial blood samples were taken at 7 different time points. The preoperative median values for u-PA antigen (u-PA Ag) and plasmin-activatable single-chain u-PA (scu-PA) levels, which were more than 2-fold above normal (both: p <0.01), decreased slightly during the preanhepatic phase and remained unchanged during the anhepatic phase. With reperfusion of the graft liver the two levels decreased significantly (p = 0.0003 and p = 0.006, respectively) to almost normal values, probably due to clearance by the graft liver. Active two-chain u-PA (tcu-PA) was preoperatively 2-fold above the detection limit, remained stable during the preanhepatic phase and increased 2-fold in the anhepatic phase (p = 0.0018). As expected tcu-PA also relapsed upon reperfusion, but to the preoperatively enhanced level, possibly caused by sustained activation of scu-PA by cathepsin B. t-PA activity levels were at the upper end of the normal range preoperatively, slightly increased during preanhepatic and anhepatic phases and decreased significantly with reperfusion. The increases in tcu-PA and t-PA activities during the anhepatic phase coincided with greatly increased fibrinolysis as demonstrated by thrombelastography, indicating that both u-PA and t-PA are involved in the development of fibrinolysis during OLT.One patient was excluded from statistical evaluations because preoperative u-PA Ag, scu-PA, tcu-PA and t-PA activity levels were much higher than in the other 28 patients. In the investigated group this patient was the only one with diffuse peritonitis intraoperatively and severe bleeding complications postoperatively which made retransplantation mandatory.
Plasma Lipids and Platelet Membrane Fluidity in Essential Hypertension
Authors: Quan Sang Kim Hanh Le , Mazeaud Madeleine , Astarie Catherine , Duranthon Véronique , Driss Fathi , Devynck Marie-Aude 
Published: July 2018

SummaryEssential hypertension is often associated with high levels of plasma cholesterol or triglycerides. The relationships between plasma lipids and platelet lipids, membrane fluidity and functions in untreated hypertensive patients were investigated by measuring the fluorescence anisotropies of two fluorescent dyes (DPH and its cationic derivative, TMA-DPH, with different subcellular localization), cytosolic Ca2+ and pH, cyclic AMP content and aggregation to ADP and collagen. Hypercholesterolemia was found to be accompanied by a rise in platelet cholesterol content without changes in TMA-DPH or DPH anisotropies whereas hypertriglyceridemia was associated with a decreased cholesterol to phospholipid molar ratio, a decreased DPH anisotropy and a tendency of the cytosol to alkalinize. These results point out the differences between the effects of an acute cholesterol load and those of chronic hypercholesterolemia on platelet membrane microviscosity and aggregation. They demonstrate a strong association between plasma triglyceride levels and platelet membrane structure.
Increased Activity of Vitamin K-Dependent Clotting Factors in Human Hyperlipoproteinaemia – Association with Cholesterol and Triglyceride Levels
Authors: Constantino M , Merskey C , Kudzma D. J , Zucker M. B 
Published: July 2018

SummaryLevels of blood coagulation factors, cholesterol and triglyceride were measured in human plasma. Prothrombin was significantly elevated in type Ha hyperlipidaemia; prothrombin and factors VII, IX and X in type lib; and prothrombin and factors VII and IX in type V. Multiple regression analysis showed significant correlation between the levels of these plasma lipids and the vitamin K-dependent clotting factors (prothrombin, factors VII, IX and X). Higher cholesterol levels were associated with higher levels of prothrombin and factor X while higher triglyceride levels were associated with higher levels of these as well as factors VII and IX. Prothrombin showed a significant cholesterol-triglyceride interaction in that higher cholesterol levels were associated with higher prothrombin levels at all levels of triglyceride, with the most marked effects in subjects with higher triglyceride levels. Higher prothrombin levels were noted in subjects with high or moderately elevated (but not low) cholesterol levels. Ultracentrifugation of plasma in a density of 1.21 showed activity for prothrombin and factors VII and X only in the lipoprotein-free subnatant fraction. Thus, a true increase in clotting factor protein was probably present. The significance of the correlation between levels of vitamin K-dependent clotting factors and plasma lipids remains to be determined.
Isolation of Antithrombin III from Normal and α1-Antitrypsin-Deficient Human Plasma
Authors: Borsodi Anna D. , Bradshaw Ralph A. 
Published: July 2018

SummaryThe plasma of individuals, hetero- or homozygous for α1-antitrypsin deficiency, contains greatly decreased amounts of antithrombin activity as assayed against factor Xa. However, heparin stimulation of the residual antithrombin activity is observed, which is comparable to that of normal plasma. Antithrombins isolated from both normal and α1-antitrypsin deficient plasma by a simplified procedure are indistinguishable in both properties and yields. The microheterogeneity observed on isoelectric focusing of both preparations can be eliminated by treatment with neuraminidase. Neither purified human antithrombin nor α1-antitrypsin, when assayed against bovine trypsin, is stimulated by heparin. These results clearly establish the unique natures of antithrombin and α1-antitrypsin and show that about 75% of the antithrombin activity measured in normal plasma is due to α1-antitrypsin. Estimates of anti thrombin III activity in normal plasma by assays dependent on enzymatic activity can probably be obtained only in the presence of heparin.
The Effect of Halofenate – Free Acid on Aggregation – the Release Reaction, Coagulant Activity, and Lipid Metabolism of Human Platelets
Authors: Akbar Huzoor- , Ardlie N. G 
Published: July 2018

SummaryHalofenate – free acid (HFA), the major metabolite of the hypolipidemic drug, halofenate, inhibited platelet aggregation induced by collagen and sodium arachidonate and blocked the second phase of aggregation caused by ADP, thrombin and epinephrine in human platelet-rich plasma. The aggregation of washed platelets by thrombin and collagen was also blocked. HFA also inhibited the release by thrombin and collagen of 5-hydroxytryptamine from dense granules of platelets and the release by thrombin of β-glucuronidase from platelet α-granules. These inhibitory effects were concentration and time-dependent. HFA decreased platelet factor 3 activity by 31 % and also inhibited the incorporation of 14C-acetate and U-14C-glucose into platelet lipids by 89 % and 56 % respectively. Thrombin-induced lipid peroxidation and prostaglandin formation was investigated by measuring the by-product malonyldialdehyde, and this was found to be inhibited by HFA. It is suggested that the effect of HFA on aggregation is attributable to inhibition of the release reaction which may in turn be a consequence of the effects of the drug on platelet lipid synthesis.