A novel high molecular weight fibrinogenase from the venom of Bitis arietans.
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A fibrinogenase (Ba100) with an apparent molecular mass of 100 kDa under non-reducing conditions and a pI of 5.4 was purified from the venom of the African puff adder (Bitis arietans) by fibrinogen affinity chromatography. Under reducing conditions the protease dissociates into subunits of 21 kDa and 16 kDa. N-Terminal amino acid sequencing showed these two chains to have 66.7% homology and homology to C-type lectins. The fibrinogenase activity of Ba100 cleaves the Aalpha and Bbeta chain of fibrinogen rendering the molecule unable to polymerise into fibrin clots. Ba100 inhibited platelet aggregation in platelet rich plasma, and clot formation in whole blood, in a concentration dependent manner. (+info)
Thrombelastographic changes and early rebleeding in cirrhotic patients with variceal bleeding.
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BACKGROUND: Routine coagulation tests do not necessarily reflect haemostasis in vivo in cirrhotic patients, particularly those who have bleeding varices. Thrombelastography (TEG) can provide a global assessment of haemostatic function from initial clot formation to clot dissolution. AIM: To evaluate TEG changes in cirrhotic patients with variceal bleeding and their association with early rebleeding. PATIENTS/METHODS: Twenty cirrhotic patients with active variceal bleeding had serial TEG and routine coagulation tests daily for seven days. The TEG variables before the day of rebleeding (n = 6) were compared with those of patients without rebleeding (n = 14). RESULTS: Baseline characteristics of the rebleeding and non-rebleeding groups were comparable apart from a higher incidence of uncontrolled infection on the day of rebleeding in the rebleeding group (p = 0.007). The patients in the rebleeding group were more hypocoagulable before the day of rebleeding as shown by longer r (42 v 24 mm, p < 0.001) and k (48 v 13 mm, p < 0.001) and smaller a (12 v 38 degrees, p < 0.001) compared with the mean of daily results of the non-rebleeding group. Routine coagulation tests, however, showed no significant differences between the two groups. CONCLUSION: The results of serial TEG measurements suggest that hypocoagulability may be associated with early rebleeding in cirrhotic patients. (+info)
Effect of 20% in vitro haemodilution with warmed buffered salt solution and cerebrospinal fluid on coagulation.
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We have conducted an in vitro coagulation study consisting of two separate groups of 20 subjects using the thrombelastograph. In the first group, haemodilution was performed with a physiological balanced salt solution similar to plasma, with the exception of calcium, and buffered to a normal pH (Plasmalyte B) at 37 degrees C on blood obtained from consenting volunteers. In the second group, a protein-poor body fluid (cerebrospinal fluid (CSF)) obtained from parturient patients undergoing spinal anaesthesia for Caesarean section was used as the diluent. There were statistically significant differences between the warmed Plasmalyte B treated samples and their untreated controls for all variables measured by the thrombelastograph, except for maximum amplitude, and between the CSF treated samples and their untreated controls for all variables. We conclude that electrolyte and acid-base composition of the diluent fluid had no effect on the observation that crystalloid haemodilution produces hypercoagulability. The marked increase in coagulability produced by addition of CSF cannot be explained on a simple haemodilution basis and confirms previous suggestions of the presence of a procoagulant factor in CSF. (+info)
Thrombelastogram reveals hypercoagulability after administration of gelatin solution.
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We have compared the effects of gelatin, low molecular weight hydroxyethyl starch (HES) or albumin on tests of haemostasis and on the thrombelastogram in 42 ASA I patients undergoing total hip or knee replacement. Patients were allocated randomly to receive one of the three blood substitutes to obtain moderate intraoperative haemodilution. Blood loss and packed red cell infusion was the same in each group. A greater amount of gelatin was given (1.5 times the measured blood loss) because of its shorter half-life. There was a statistically significant but clinically negligible decrease in platelets count, prothrombin time and fibrinogen, and an increase in bleeding time in all groups. Platelets were slightly but significantly lower after HES. Haemodilution was comparable between groups. TEG showed a state of hypercoagulability in the gelatin group with a significant decrease in r, r + k and an increase in alpha angle. (+info)
Pro-coagulant effect of in vitro haemodilution is not inhibited by aspirin.
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We have conducted an in vitro coagulation study, using the thrombelastograph (TEG), to determine if the enhanced coagulability of whole blood after haemodilution with normal saline can still be demonstrated after administration of an antiplatelet agent. Aspirin inhibits the platelet-endothelial interaction that is part of the coagulation process. We investigated the role of aspirin in the phenomenon of haemodilution-induced coagulability to identify if the platelet-endothelial system is involved in the process. Previous work showed that the TEG is not altered by oral ingestion of aspirin. Blood from 20 volunteers was divided into two aliquots of 4 ml each. One sample was diluted by 20% by addition of 0.9% saline 1 ml while the other was not diluted and served as a control. Coagulation studies were performed using the TEG and enhanced coagulation was seen in the saline diluted samples. Subjects then received soluble aspirin 375 mg daily for 3 days, after which the tests were repeated. There was no difference in the control TEG values and saline enhancement of coagulation was preserved in all subjects after 3 days of aspirin administration. We conclude that aspirin had no effect on the observation that haemodilution with saline enhances the coagulability of whole blood. (+info)
Comparative in vitro efficacy of different platelet glycoprotein IIb/IIIa antagonists on platelet-mediated clot strength induced by tissue factor with use of thromboelastography: differentiation among glycoprotein IIb/IIIa antagonists.
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In the present study, the in vitro efficacy of different platelet glycoprotein IIb/IIIa (GPIIb/IIIa) antagonists on platelet-fibrin-mediated clot strength under shear was compared with the antiaggregatory efficacy by using tissue factor (TF) thromboelastography (TEG). The ability of platelets to augment the elastic properties of blood clots under shear conditions was measured by computerized TEG under conditions of maximal platelet activation accelerated by recombinant TF. Under these conditions, platelets significantly enhance clot strength 8-fold (relative to platelet-free fibrin clots). This effect was inhibited to a different extent by various platelet GPIIb/IIIa receptor antagonists; this inhibition appears to be dependent on the transmission of platelet contractile force to fibrin via the GPIIb/IIIa receptors. The GPIIb/IIIa antagonists with high binding affinity for resting and activated platelets and slow platelet dissociation rates (class I) but not those with fast platelet dissociation rates (class II) demonstrated potent and comparable inhibition of platelet aggregation and TF-TEG clot strength. Platelet GPIIb/IIIa antagonists of class I, such as XV459 (free-acid form of roxifiban), DMP802, XV454, and c7E3, demonstrated comparable inhibitory dose responses of TF-TEG clot strength and platelet aggregation, with an IC(50) of 50 to 70 nmol/L. In contrast, platelet GPIIb/IIIa antagonists from class II, with comparable antiaggregatory efficacy, such as DMP728, YZ202 (free-acid form of orbofiban), YZ211 (free-acid form of sibrafiban), YZ751, and other antagonists, have a much lower efficacy in altering the strength of TF-mediated clot formation (IC(50) >1.0 micromol/L). These data suggest differential efficacy among different GPIIb/IIIa antagonists in inhibiting platelet-fibrin clot retraction despite of equivalent antiaggregatory potency. (+info)
BACKGROUND: Thrombelastograph analysis (TEG) is used to evaluate blood coagulation. Ideally, whole blood is immediately processed. If impossible, blood may be citrated and assessed after recalcification. No data describe the effect of such treatment and storage on TEG parameters. METHODS: Three studies were performed in 90 surgical patients. In 30 patients, blood was citrated (1:10, 0. 129 M) and recalcified (20 microl 2 M CaCl2 to 340 microl citrated blood), and TEG was performed with native blood and after recalcification after 0, 15, and 30 min of citrate storage. In another 30 patients, TEG was performed with citrated blood recalcified immediately and after 1-72 h storage. In a third study, thrombin-antithrombin complex, prothrombin fragment 1+2, and beta-thromboglobulin were measured (using enzyme-linked immunoabsorbant assay tests) at corresponding time points. Data were compared using repeated-measures analysis of variance and post hocpaired t tests. RESULTS: TEG parameters were different in recalcified citrated blood compared with native blood (P < 0.05) and changed significantly during 30-min (P < 0.025) and 72-h (P < 0.001) citrate storage. TEG parameters measured between 1 and 8 h of citrate storage were stable. Thrombin-antithrombin complex and prothrombin fragment 1+2 values were not elevated in native blood. After 30 min of citrate storage a gradual thrombin activation was observed, as evidenced by increasing thrombin-antithrombin complex and prothrombin fragment 1+2 values (P < 0.05). beta-Thromboglobulin level was increased after 2 and 8 h of citrate storage (P < 0.01). CONCLUSIONS: Analysis of native blood yields the most reliable TEG results. Should immediate TEG processing not be possible, citrated blood may be used if recalcified after 1-8 h. (+info)
Preparation for regional anaesthesia induces changes in thrombelastography.
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The effects of crystalloid and colloid infusions on coagulation measured by thrombelastography (TEG) present a confused picture. The influence of environmental factors may explain the disparity between previous studies. We studied two groups of 20 women presenting at term for elective Caesarean section. In the first group, TEG analysis was performed before and after infusion of Gelofusine 500 ml over 15 min. The second group was treated in the same way except that subjects did not receive fluid. We found significant changes in r and k values in both groups, suggesting enhanced coagulation. As hypercoagulable changes were also seen in the group that did not receive fluid preload, the hypothesis that moderate haemodilution causes hypercoagulability must be questioned. The influence of environmental factors can explain differences reported between in vivo and in vitro studies. (+info)