[From heparin to heparins: toward new therapeutic perspectives?]

Heparin is mainly known for its anticoagulant action, but today other biological effects are investigated. With the low molecular weight heparin fractions (LMWH), more homogenous, a more detailed study of the mechanism of action of heparins can be made. The anticoagulant action of heparin is mainly antithrombin III (AT III) dependent and the binding site of AT III on the heparin molecule has been recently identified. LMWH have a lower anticoagulant (anti-IIa) activity, and a relatively higher anti-Xa activity (ratio anti-Xa/anti-IIa = 5 to 10 for LMWH and 1 for standard heparin). The antithrombotic action of heparins is not strictly correlated to their anticoagulant activity. Other mechanisms of action, such as interactions with vascular endothelial cells and the fibrinolytic system may contribute to the antithrombotic action of heparins. New therapeutical possibilities are currently under investigation. Inhibition of vascular smooth muscle cells growth by heparin suggest a possible control of the atherosclerotic process by heparin. Moreover, heparin and its derivatives might be involved in the regulation of the cellular growth process.