[Antithrombotic properties of heparin independent of its anticoagulant activity]

Antithrombotic effects of two glycosaminoglycans: LMWH-Fraxiparin (Sanofi) and UFH Heparinum (Polfa) have been studied in the laser-induced rat thrombosis model. The investigations were carried out on male Wistar rats. Thrombus formation was induced in small mesenteric venules 25-30 microns in diameter using argon laser. An interference contrast system based on a Leitz Orthoplan microscope was used for the evaluation of thrombus formation. The number of laser injuries needed to induce a defined thrombus proved to be a useful way to quantitate the results in this thrombosis model. Fraxiparin and UFH showed doses dependent antithrombotic effect in the laser model. Fraxiparin in minimal dose 16 aXa/kg and UFH in minimal dose 15 IU/kg 30 min after i.v. injection to the rats markedly inhibited thrombus formation in small mesenteric venules. Antithrombotic effect of the administration of minimal effective doses of both glycosaminoglycans lasted longer than 4 hours but less than 6 hours. Protamine injected in a dose 1 ml per 5000 U/heparin neutralized anticoagulant activity of both heparins in rat plasma but did not inhibit the antithrombotic effect in laser thrombosis model. After the injection of protamine antithrombotic effect of the investigated glycosaminoglycans was weaker but still observed. Further studies are needed to clarify the factors which are responsible for the antithrombotic effect of heparins after neutralization of their anticoagulant activity (inhibition factors: IIa and Xa).