Fibrin network structure: modification by platelets.

Platelets play a fundamental role in haemostasis and thrombosis. They are known to undergo characteristic changes including release of subcellular material during clotting. The effect of subcellular platelet material on fibrin network structure, however, has not previously been investigated. Using opacity ratio, syneresis, permeation and electron microscopy it was found that subcellular platelet material extracted into NaCl is able to influence fibrin network structure of clots made from purified fibrinogen as well as platelet-poor plasma. Such clots had higher opacity ratio, reduced syneresis and lower permeability than control clots. Further, the responsible platelet material is heat labile and is released from the platelets during their aggregation with several common aggregating agents. Morphometric analysis of transmission electron micrographs has shown that fibrin fibres in plasma clots made in the presence of platelet subcellular material are thinner than those in control clots. In addition, plasma clots made in the presence of platelet extract had a higher resistance to fibrinolytic digestion than control clots. Thus, platelets play a hitherto undescribed role in regulating fibrin network structure.

Preoperative blood tests in prediction of postoperative deep vein thrombosis.

Fifty six patients undergoing elective abdominal surgery were investigated preoperatively with tests of coagulation, platelet function and fibrinolysis. Ten patients developed postoperative deep vein thrombosis, detected by the labelled fibrinogen uptake test and confirmed by ascending phlebography. None of the tests showed a statistically significant difference between the group mean of patients who developed DVT and of those who did not. Potential discriminators were used to derive a prognostic index for prediction of patients who would develop postoperative DVT. An index based on two preoperative blood tests i.e. three hour fibrin digestion and APTT had a successful prediction rate of 59 percent.

An evaluation of the British Pharmacopoeial assay of heparin: a comparison with other methods.

The potencies of six commercially manufactured heparins have been measured by the British Pharmacopoeial (BP) assay and activated partial thromboplastin time (APTT), protamine sulphate, and anti-Xa assays. The APTT/BP potency ratios were found to vary with the preparation but this was not dependent on the tissue source of heparin. For mucosal heparins, the anti-Xa/BP potency ratios were close to unity, but for heparin of lung origin the anti-Xa potency was approximately one-quarter of the BP potency. Four heparin fractions prepared by column gel chromatography of a commercial heparin were similarly examined by all four assays, and there was a wide divergence between the BP potency estimates and those obtained with the other methods. The degree of divergence was found to depend on the molecular size of the fraction.

Effects of dextran on the molecular structure and tensile behaviour of human fibrin.

Characteristic changes induced by dextran during the conversion of fibrinogen to fibrin have previously been shown to be associated with profound alterations in morphology of fibrin. However, whether dextran is incorporated into the fibrin molecule and whether morphological changes are associated with alterations in mechanical behaviour of formed fibrin was unclear. The investigations described show that the fibrin made in the presence of dextran has a shortened syneresis time, a lowered modulus of elasticity, an increased elongation and diminished ultimate strength at break. The molecular composition of fibrin clots remains unaltered despite the altered mechanical properties and morphological changes. Furthermore, dextran is not incorporated into the fibrin structure in any appreciable quantity. It is suggested that these several effects of dextran on clot morphology, tensile behaviour and kinetics of fibrin formation arise from increased forces of attraction between fibrin molecules such that fibrin chains are held together by weak secondary cross-links rather than by stronger primary cross-links which are hidden within the thicker fibrin chain bundles.