In a randomized, blind study the primary effect on haemostasis after intravenous administration of dermatan sulphate (DS), recombinant hirudin (r-hirudin) and four commercial low molecular weight heparins (LMWHs) (nadroparine, enoxaparin, dalteparin and tinzaparin) was investigated in rats and compared with saline (control). The tail bleeding time, the bleeding from the gastric mucosa [the mucosal bleeding time (min) and the mucosal bleeding (μ1)] as well as changes in activated partial thromboplastin time, antifactor IIa and Xa activities were investigated. DS and r-hirudin were investigated in a dose potentially suitable in thomboprophylaxis and the LMWHs in doses recommended by the manufacturers for thromboprophylaxis, adjusted to body weight. All substances significantly prolonged the mucosal bleeding time. Dalteparin, tinzaparin, DS and r-hirudin increased the mucosal bleeding when compared with controls whereas nadroparine and enoxaparin did not. The effect of r-hirudin was also significantly more pronounced compared with other treatments. Moreover, r-hirudin prolonged the tail bleeding time significantly whereas the other substances did not. The antifactor Xa activity in plasma correlated well with the given dose of the LMWHs (r_s = 0.7). However, the monitored bleeding parameters in the LMWH groups did not correlate with the plasma activities of antifactor IIa or Xa. The results indicate that the tested LMWHs are not equipotent in their effect on haemostasis in this model and that antifactor Ha or Xa activities do not directly correlate with their effect on haemostasis although increased haemorrhage was observed in the LMWHs with lower antifactor Xa/antifactor IIa ratios. Our findings indicate that the different commercial LMWHs may differ in their haemorrhagic effect when given in recommended clinical doses adjusted to body weight. DS (3.0 mg/kg) did not cause more bleeding than the tested LMWHs but r-hirudin (2.0 mg/kg) caused considerable bleeding.

Twenty-four arteries of rabbit ears, divided into three groups of eight, were prepared and 32P-platelets injected. Arteriotomy (7 mm) and intimectomy (5 mm) were performed and in vivo platelet accumulation followed for 2 hours. Group A comprised untreated control animals, group B was treated with 17 ml saline/kg bw, and group C with 1 g dextran and 17 ml saline/kg bw (Macrodex). Significant differences in platelet accumulation were observed only between the control and Macrodex groups at 105 and 120 minutes. In the control and saline groups four of eight vessels showed poor or no patency. All Macrodex vessels showed good patency. Control and saline vessels had large amounts of red thrombotic material, except for three saline cases with small amounts. After Macrodex treatment five of eight vessels were apparently clean, while the other three showed only small amounts of red thrombotic material. Dextran seems not to influence platelet function but rather to inhibit fibrin stabilization and probably increases fibrinolysis. Vascular patency was only endangered by the formation of solid fibrin-containing red thrombi.

SummaryThe glycosylated multivalent three-domain Kunitz inhibitor TFPI is a natural inhibitor of tissue factor-FVIIa complex in the presence of FXa. TFPI has an experimental antithrombotic capacity indistinguishable from LMWH in a prophylactic dose, regardless of glycosylation and of the third domain. An inherited equilibrium between antithrombosis and haemorrhage exists. The aim of the study was to evaluate whether a two-domain non-glycosylated TFPI (117QTFPI1−161) has a bleeding potential in a rat gastric mucosa model. Groups; placebo, LMWH (tinzaparin) 60 and 250 anti-Xa IU/kg and 117QTFPIM61−161 1.0 and 10.0 mg/kg, given i.v. (bolus injection), randomised double dummy design.All actively treated groups significantly prolonged both the bleeding volume (493-984 Μl) and the bleeding time (10-20 min) compared to placebo (41 Μl, 2 min). It was not possible to distinguish a difference between the lower dose of LMWH and 117QTFPI1−161 in either parameter (p = 0.23-0.71). The two doses of 117QTFPI1−161 caused elevation of plasma-TFPI, 18 and 150 times baseline value. Both LMWH doses (0.6-3.2 anti-Xa IU/ml) and both 117QTFPI1−161 doses (0.2-2.7 anti-Xa IU/ml), caused significant effect in the anti-Xa assay, however 117QTFPI1−161 significantly less. Only the largest dose of 117QTFPI1−161 caused significant prolongation in the APTT assay (34 s). Both doses of LMWH caused significant prolongation (60-300 s). LMWH was the only substance to prolong the dilute-PT assay.Non-glycosylated two-domain 1.0 mg/kg TFPI, yielding supra-physiological plasma concentration, has an experimental haemorrhagic potential indistinguishable from LMWH in a prophylactic dose. The effect mediated by this type of TFPI could primarily be due to an inhibition of FXa.

No abstract