title: Mode of action of unfractionated and low molecular weight heparins on the generation of thrombin in plasma.
abstract: Heparins, unfractionated and low molecular weight, act primarily by their scavenging of thrombin (S-type heparins). Via the feedback effect on factor VIII this has a secondary effect on prothrombin conversion in the intrinsic pathway (activated partial thromboplastin time). The anti-Xa action of a heparin will not significantly inhibit prothrombin conversion, except in the case of ultra low molecular weight heparins (P-type heparins) that have no significant antithrombin activity. These P-type heparins need, therefore, be given at high doses to have an antithrombotic effect. In platelet-rich plasma heparins retard platelet activation by lowering thrombin levels. Activated platelets neutralize up to 0.5 U/ml of unfractionated heparin, but low molecular weight heparin is much less affected.
authors.affiliation: Department of Biochemistry, University of Limburg, Maastricht, The Netherlands.
authors.forename: H C
authors.initials: HC
authors.lastname: Hemker
authors.forename: S
authors.initials: S
authors.lastname: Béguin
mesh_terms: D000818:Animals; D005246:Feedback; D006493:Heparin / Q000494:pharmacology*; D006495:Heparin, Low-Molecular-Weight / Q000494:pharmacology*; D006801:Humans; D013917:Thrombin / Q000096:biosynthesis* / Q000187:drug effects
chemical_list: D006495:Heparin, Low-Molecular-Weight; D006493:Heparin; D013917:Thrombin