Characterization of serum fibrinogen and fibrin fragments produced during disseminated intravascular coagulation

The fibrinogen and fibrin degradation products (FDP) in serum samples taken from nine patients with suspected disseminated intravascular coagulation have been characterized using a method of immunoprecipitation followed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Aall of the serum samples contained a fragment with the same electrophoretic mobility as fibrinogen fragment X, while the majority also had evidence of fragments with similar mobility to fibrinogen fragments Y and D. In eight of the nine serum samples there was strong evidence of the D-dimer fragment that is released by plasmin lysis of crosslinked fibrin. Also present in all but one of the samples were fragments of higher molecular weight than fibrinogen which were probably soluble, non-clottable, factor XIIIa induced crosslinked derivatives of fibrinogen. These results suggest that during disseminated intravascular coagulation thrombin and activated factor XIII act upon fibrin(ogen) to form complexes that are subsequently lysed by plasmin to produce soluble crosslinked derivatives of fibrin.

Comparison of heparin and a semi-synthetic heparin analogue, A73025. II. Some effects on platelet function

A comparison has been made of some effects of a semi-synthetic heparin analogue, A73025, and heparin upon platelet function. In several of the in vitro tests performed, such as their potentiating effects on ADP and adrenaline induced aggregation and their effects on the aggregation of washed platelets by activated factor X, heparin proved to be more potent than A73025. Following intravenous injection of twice the quantity of A73025, an equivalent anti-factor Xa activity was obtained, in the agreement with our previous studies. However, it was found that PRP containing heparin and A73025 with comparable anti-Factor Xa acitvity responded differently to the addition of thrombin, as A73025 barely inhibited thrombin induced aggregation. Similarly, A73025 had little effect on the dilute thrombin clotting time of plasma, following intravenous injection. Heparin and A73025 were neutralized to approximately the same degree by a crude PF4 preparation.

Comparison of heparin and a semi-synthetic heparin analogue, A73025. I. Kinetics of clearance from the circulation of man following intravenous injection

A study has been made of a low molecular weight semi-synthetic heparin analogue, A73025, that may be clinically useful as an antithrombotic agent because of its reported high specificity for antithrombin III. The clearance from the circulation of both heparin and the analogue has been studied in man following intravenous injection. Heparin obeyed almost first order kinetics when assayed using a specific anti-Xa assay and first order kinetics when measured with KCCT. At high concentrations the heparin analogue was cleared with first order kinetics when assayed both with the anti-Xa assay and with KCCT. At low concentrations the analogue produced between one half and two-thirds of the anti-Xa activity of an equal dose of heparin, producing only a small prolongation of KCCT. With increasing dose, the more specific anti-Xa potentiating effect of A73025 decreased because of a flattening of its anti-Xa dose-response curve. These results suggest that the analogue might be useful as an antithrombotic agent when it is used as a prophylactic agent.

Intermittent plasminogen-streptokinase treatment of deep vein thrombosis

The fibrinolytic response of 12 patients receiving single daily infusions of 600,000 units of streptokinase (SK) and 90 mg of plasminogen for the treatment of DVT has been studied. The mean plasminogen concentration was maintained throughout the treatment period (4-6 days) at between 20-40% the initial value, while mean circulating plasmin concentration rose to only about twice initial plasma levels. The degradation of fibrinogen as indicated by a fall in clottable fibrinogen did not fall below 1 mg/ml and serum FDP rose to greater than 1 mg/ml. Limited fibrinogenolysis occurred in 2 patients, while in another patient who bled there was immediate and extensive depletion to below 0.5 mg/ml. The beneficial clinical results obtained with this regimen (Kakkar et al. 1975), which produces only limited systemic plasminaemia, suggest that thrombolysis may be facilitated by higher levels of plasminogen than those maintained during conventional SK treatment.

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.

A heparin analogue with specific action on antithrombin III

The effects of heparin and a semi-synthetic heparin analogue were compared in vivo and in vitro. The two drugs differed strikingly in their in-vitro behaviour: unlike heparin, the heparin analogue had little effect in a specific heparin assay or on overall clotting, as measured by the kaolin-cephalin clotting time (K.C.C.T.). When given by parenteral injection, the heparin analogue had almost the same potentiating effect on antithrombin III as mucous heparin, but without a comparable effect on the K.C.C.T. These observations suggest that the heparin analogue may have desirable characteristics for the prophylaxis of venous thrombosis, since it selectively potentiates antithrombin III in vivo while having little effect on overall clotting.

A comparison of the sulphite and thrombin methods for measuring fibrinogen concentration of plasma from patients undergoing thrombolytic therapy

A thrombin method for the determination of fibrinogen concentration has been compared with a non-enzymatic sulphite precipitation method on plasma from patients undergoing thrombolytic therapy with an intermittent plasminogen/streptokinase regime. There was very good agreement between the methods even when the determinations were made in the presence of high levels of fibrinogen degradation products (FDP), provided that the thrombin clottable fibrinogen was greater than 1 mg/ml. However, after extensive fibrinogen depletion, when the thrombin method underestimates fibrinogen concentration due to significant clot inhibition by FDP, an overestimate due to co-precipitation of fragments X and Y will be obtained by the sulphite method. This suggests that the simultaneous application of both techniques may provide a simple method of assessing the presence of high levels of anticoagulant FDP in various clinical disorders.

Effect of low-dose subcutaneous heparin on whole-blood viscosity

The change in blood-viscosity at low shear-rates (0.77 s-1 and 2-62 s-1 was measured in eighteen normal subjects and postoperatively in sixteen patients after administration of 5000 I.U. of subcutaneous heparin. In both groups there was a significant decrease in the mean blood-viscosity 4 to 6 hours after the injection of heparin. This fall in blood-viscosity may be involved in the prophylactic effect of low-dose subcutaneous heparin in preventing venous thrombosis.

Soluble high-molecular-weight E fragments in the plasmin-induced degradation products of cross-linked human fibrin

1. The factor XIII-mediated cross-linked alpha chains in fibrin have no effect on the nature of the fragments released during the solubilization of fibrin by plasmin. 2. Besides the known D dimer and E fragments solubilized during the lysis of cross-linked fibrin, other fragments have been observed on sodium dodecyl sulphate-polyacrylamide gel electrophoresis which have a molecular weight of about 135 000. After prolonged plasmin digestion, these fragments (U fragments) were no longer evident on the gels and the high-molecular-weight E antigen was absent. It is assumed that the E antigen was associated with the U fragments. These fragments also cross-reacted with an anti-D serum. 3. The U fragments have been tentatively presumed to be a factor XIII-mediated cross-linked D-E complex since they degrade only after prolonged degradation with plasmin. Whereas it is known that the fibrin D dimer fragment contains the cross-linked gamma chain residues of the originating fibrin, the presumed covalent cross-linking of the D-E fragments has not been proved. 4. The presence of these high-molecular-weight fragments, containing the E antigen, in cross-linked human fibrin digests should be taken into account in the development of D dimer assays to monitor fibrin lysis in vivo.

The variation of indicator dilution curves with velocity profile

A theoretical analysis has been made of the effect of different velocity profiles on the dispersion of a non-diffusable solute in fluid flow down a straight tube. An experimental investigation of this type of dispersion was made by monitoring the transport of radioactively labelled red blood cells in whole blood at flow rates within the non-Newtonian viscosity range. The dispersion curves obtained are consistent with a progressive flattening of the velocity profile as the flow rate is reduced, though a more rapid clearance than that predicted theoretically occurs in the tail region of the curves. The accepted indicator dilution techniques of estimating the flow rate and vessel volumes are considerably in error. An alternative method of accurately estimating the vessel volume is suggested.