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At least 289 records · Page 16Linked to original sources
PubMed1975

Dissociation of clot retraction from platelet granule fusion and degranulation: an ultrastructural study of Reptilase-human platelet-rich plasma clots.

Human platelet-rich plasma clots, formed with Reptilase, do not retract. Electron microscopy of such a clot reveals platelets of normal shape and ultrastructural features surrounded by fibrin. When ADP is added before Reptilase, the clot strongly retracts. A sequential ultrastructural study of this process shows that, before visible fibrin formation, the platelets form small clusters and show shape change, granule centralization and pseudopod formation. Upon immobilization of the platelets by fibrin, the pseudopods develop into large cytoplasmatic protrusions, which allow cell contact. During the retraction process, the platelet granules remain intact; some granule fusion only becomes apparent in fully retracted clots. When Thrombofax is added to platelet-rich plasma before Reptilase, the clots formed also retract. With this aggregation inducer, granule fusion occurs earlier and in more platelets. Platelet pseudopod enlargement and fibrin concentration around the platelet mass are similar to that in ADP-treated samples. Inhibitors of granule fusion and secretion (suprofen, indomethacin) do not modify ADP-Reptilase nor Thrombofax-Reptilase clot retraction but reduce the incidence of granule fusion in Thrombofax-Reptilase clots. Retraction of Thrombofax-Reptilase clots is unaffected by concentrations of apyrase which completely block ADP-Reptilase clot retraction. Prostaglandin E1, papaverine and amitryptiline inhibit both ADP-and Thrombofax-Reptilase clot retraction, platelet pseudopod formation and cell-to-cell adhesion. These findings suggest that interaction of fibrin with the mass of fused granules (granulomere) or platelet secretion are not responsible for clot retraction. Rather, contraction around adhesion sites formed by cytoplasmic protrusions from adjacent platelets would seem to be involved.

Adenosine Diphosphate↗
PubMed1975

Alternative pathways for the activation of factor XIII.

Factor XIII is present in plasma as a proenzyme, which when activated catalyses the formation of epsilon(gamma-glutamyl)lysyl bonds in fibrin. In this study the activation of purified plasma factor XIII was examined quantitatively with the fluorescent amine incorporation assay. Activation products were examined by polyacrylamide gel electrophoresis. The serin proteases, thrombin, trypsin, chymotrypsin, and factor Xa, and also Reptilase were tested for their ability to activate factor XIII. Highly purified thrombins activated purified factor XIII; this reaction was not calcium dependent. Trypsin was also a potent activator, but no transglutaminase activity was found with chymotrypsin. The most highly purified preparations of Reptilase had no effect on factor XIII activity. Less purified Reptilase preparations activated factor XIII, which suggests the presence of another enzyme in these Reptilase preparations. Highly purified factor Xa was found to be an effective activator of purified factor XIII. In contrast to thrombin activation, this reaction required calcium. It may be that under certain circumstances factor XIIIa could be formed in vivo directly by the alternative pathway of factor Xa. Factor XIIIa could then crosslink fibrinogen, which would also provide an alternative pathway for thrombus formation. Also, the activation of factor XIII by both factor Xa and thrombin provides a further point of control in the blood coagulation process.

Batroxobin↗
PubMed1976

Factor VIII and human platelet aggregation. II. Characteristics of aggregation of human platelets by bovine factor VIII.

Bovine factor VIII aggregates human platelets either in a strong single wave at high concentration (10 mug/ml platelet suspension) or in two waves at low concentration (0.2-I mug/ml). The strong single wave of aggregation is not associated with release of [14C]serotonin or beta-glucuronidase; the high concentration does not induce retraction of reptilase-clotted platelet-rich plasma. Wtih the low concentration, relase of [14C]serotonin is observed just prior to the onset of the second wave of aggregation; release of beta-glucuronidase does not occur at any moment. The low concentration of bovine factor VIII induces moderate retraction of reptilase-clotted platelet-clotted platelet-rich plasma, which is inhibited by acetylsalicylic acid, indomethacin and apyrase, indicating that it is a consequence of release of platelet adenosine-5'-diphosphate. It has previously been suggested tht carbohydrate groups are involved in the human platelet-bovine factor VIII interaction, since galactose oxidase and periodate oxidation abolish the platelet aggregating activity of bovine factor VIII. The present study shows that these oxidizing substances also induce a degradation of bovine factor VIII, so that the exact role of carbohydrate groups in the aggregation process remains to be established.

Animals↗
PubMed1976

Abnormal fibrin polymerization in liver disease.

Although there have been isolated reports of an acquired abnormal fibrinogen in patients with liver disease, its frequency and clinical significance is not known. In this study 121 consecutive patients with a wide spectrum of hepatic disorders were screened for abnormal fibrin polymerization. A simple colorimetric method using Reptilase was employed. Of 32 patients with proven cirrhosis, 16 (50%) showed abnormal fibrin polymerization. The incidence in decompensated alcoholic cirrhosis was particularly high. The abnormality was also detected in all patients with acute liver failure and seven of 15 with chronic active liver disease. Clinical improvement often correlated with its disappearance. Two patients with primary liver cell tumours demonstrated the abnormal polymerization. In patients with bleeding oesophageal varices the detection of abnormal fibrin polymerization was associated with a poor prognosis. None of the patients with surgical obstructive jaundice (26) or miscellaneous liver disorders (37) had abnormal fibrin polymerization. The occurrence of abnormal fibrin polymerization in liver disease is more frequent than previously suspected and usually signifies severe primary hepatocellular dysfunction. Evidence is presented to support the presence of a primary abnormality of fibrinogen as the cause of impaired fibrin monomer polymerization.

Batroxobin↗
PubMed1977

Acquired dysfibrinogenaemia in acute and chronic liver disease.

Plasma from patients with both acute and chronic liver disease has been examined for evidence of acquired dysfibrinogenaemia, using electrophoretic methods and coagulation tests. An examination of isolated fibrins upon SDS polyacryamide gel electrophoresis failed to demonstrate any molecular or structural defect associated with the polypeptide chains of the patients' fibrinogen or fibrinogen derivatives produced by thrombin or plasmin. However, purified fibrin monomers isolated from plasma using both Reptilase and thrombin exhibited delayed polymerization rates and the occurrence of acquired dysfibrinogenaemia in liver disease is therefore confirmed.

Acute Disease↗
PubMed1979

Plasma administration to defibrinogenated dogs during extracorporeal circulation.

Plasma, in an amount corresponding to 0.05 gm fibrinogen/Kg of body weight, was administered during one hour to defibrinogenated dogs subjected to extracorporeal circulation. Four blood filters included in the extracorporeal circuit were removed one by one at 30-minute intervals. The prefilter pressures rose gradually during the whole experiment. Scanning electron microscopy of the filter surface revealed equal amounts of deposits before, during and after the infusion of plasma. Only minimal amounts of fibrin were found on the filter surfaces by immunoelectrophoresis. Mean arterial pressure, arterial blood gases, fibrinogen concentration, platelet count and leukocyte count were followed before, during and after plasma infusion and showed no significant changes. Thus, it is possible to administer limited amounts of plasma to defibrinogenated dogs subjected to extracorporeal circulation.

Animals↗
PubMed2005

Functional analysis of recombinant Bbeta15C and Bbeta15A fibrinogens demonstrates that Bbeta15G residue plays important roles in FPB release and in lateral aggregation of protofibrils.

BACKGROUND AND OBJECTIVES: Analysis of dysfibrinogens has improved our understanding of molecular defects and their effects on the function of intact fibrinogen. To eliminate the influence of plasma heterozygous molecules, we synthesized and analyzed recombinant-variant fibrinogens. METHODS: We synthesized two recombinant-variant fibrinogens with a single amino acid substitution at the 15Gly residue in the Bbeta-chain: namely, Bbeta15Cys and Bbeta15Ala. RESULTS: Western blotting analysis of purified fibrinogen revealed the existence of a small amount of a dimeric form only for Bbeta15Cys fibrinogen. For Bbeta15Cys fibrinogen, functional analysis indicated (a) no thrombin-catalyzed fibrinopeptide B (FPB) release and (b) markedly impaired lateral aggregation in thrombin- and reptilase-catalyzed fibrin polymerizations. For Bbeta15Ala fibrinogen, such analysis indicated slight impairments of both thrombin-catalyzed FPB release and lateral aggregation in thrombin-catalyzed fibrin polymerization, but nearly normal lateral aggregation in reptilase-catalyzed fibrin polymerization. These impaired lateral aggregations were accompanied by thinner fibrin fiber diameters (determined by scanning electron microscopy of the corresponding fibrin clots). CONCLUSION: We conclude that a region adjacent to Bbeta15Gly plays important roles in lateral aggregation not only in desA fibrin polymerization, but also in desAB fibrin polymerization, and we speculate that the marked functional differences between Bbeta15A and Bbeta15C fibrinogens in FPB release and fibrin polymerization might not only be due to the presence of a substituted cysteine residue in Bbeta15C fibrinogen, but also to the existence of disulfide-bonded forms. Finally, our data indicate that the Bbeta15Gly residue plays important roles in FPB release and lateral aggregation of protofibrils.

Alanine↗
PubMed1975

Activated reptilase clot retraction of dog platelet-rich plasma: differences with human platelet-rich plasma.

The retraction of dog platelet-rich plasma (PRP) clotted with Reptilase in the presence of inducers and inhibitors of the platelet adhesion-aggregation reaction was studied. In contrast to human cells, dog platelets fail to support retraction in an ADP-Reptilase system. With Thrombofax as aggregation inducer, slight (without additional CaCl2-MgCl2) to moderate (with additional CaCl2-MgCl2) retraction occurs. In contrast to human samples, such retraction is inhibited by platelet release inhibitors. Electron-microscopic examinations show that Thrombofax, but not ADP, induces the formation of large cytoplasmic protrusions from dog platelets. Such formation is inhibited by release-inhibitors. The results of the study support the concept that platelet pseudopod formation, rather than the release reaction, is a prerequisite for clot retraction.

Adenosine Diphosphate↗
PubMed1976

Reptilase clot retraction induced by electrical stimulation.

Retraction of platelet rich plasma clotted by reptilase is induced by electrical stimulation. Optimal retraction is obtained by stimuli, applied for more than 4 min, with the following characteristics: intensity = 150 volts, duration = 50 msec each, frequency = 10/sec. Electrically induced reptilase clot retraction is shown to be inhibited by EDTA, EGTA, methyl-xanthines, PGE1, acetylsalicylic acid, indomethacin, but not by apyrase or by phosphoenolpyruvate-pyruvate kinase and MgCl2. The results indicate that electrical stimulation induces retraction of PRP clotted by reptilase by triggering off an increased availability of Ca2+ in the intracellular space.

Apyrase↗
PubMed1976

Mechanism of calcium-induced reptilase clot retraction.

Calcium ions induce retraction of reptilase clots. This could also be induced by thrombin. Heparin inhibited the reptilase clot retraction induced either by thrombin or calcium, but did not influence the clot retraction induced by ADP. This indicated that the clot retraction induced by Ca2+ was mediated by an activation of the coagulation system with the formation of thrombin.

Adenosine Diphosphate↗
PubMed1984

Dysfibrinogenaemia associated with a defect in the aggregation of the fibrin monomers (Almeria I fibrinogen). A preliminary study.

A patient with functionally defective fibrinogen has been studied. Fibrinogen Almeria I was found to have a prolonged of latency time (LT) and a decrease in rate of gelation (RG) when plasma or isolated fibrinogen were activated by thrombin or reptilase. This fibrinogen also has the unusual formation of cross-linked fibrin; the existence of unpolymerized alpha chains was confirmed.

Adult↗
PubMed1978

Dysfibrinogenaemia and liver cell growth.

From the evidence presented, it is proposed that 'dysfibrinogenaemia' represents the production of normal fetal fibrinogen by rapidly proliferating liver cells in both regenerating and neoplastic tissue. Prolongation of the reptilase clotting time, which was formerly believed to reflect dysfibrinogenaemia, may be rather the result of hepatocytic death.

Batroxobin↗
PubMed1977

Role of fibrinopeptide B release: comparison of fibrins produced by thrombin and Ancrod.

The gelation time, opacity, light scattering, and elastic moduli of human fibrin gels clotted in the presence of thrombin, Ancrod, and Reptilase have been compared. At low ionic strength lateral association to thick fibers is observed in all cases. At all ionic strengths thrombin fibrin forms thicker fibers than does Ancrod fibrin. We have demonstrated that an increase in the extent of lateral association is linked to an increase in its velocity and to a decrease in the gelation time. One may consider the removal of fibrinopeptide B to act as a switch: after it is removed fibrin assembles rapidly to thick fibers and gelation is fast; but when this peptide is still attached, there is a slow assembly of thin fibers, and gelation, especially of dilute fibrin, is delayed. We believe that this delay is critical for the complete digestion by plasmin of fibrin formed during in vivo defibrination with Ancrod and of fibrin produced by very small amounts of thrombin (which would still contain fibrinopeptide B), and that slow release of fibrinopeptide B is part of a control mechanism for the regulation of fibrin formation and the prevention of intravascular coagulation.

Ancrod↗