In vivo effects of a low molecular weight heparin fragment on platelet aggregation and platelet dependent hemostasis in dogs

Plasma defibrinogenated dogs were used to study the influence of conventional heparin and a low molecular weight heparin fragment (Fragmin, mean MW 5,000 d) on platelet dependent hemostasis. The heparins were given intravenously in gravimetrically equal doses. The bleeding from standardized skin flap wounds and platelet aggregation (ADP and thrombin) was studied. In comparison, higher doses of the fragment than of heparin were required to increase the bleeding. ADP-induced aggregation in defibrinogenated platelet rich plasma (after addition of normal dog plasma) was potentiated by both heparins. After injection of heparin or the fragment, ADP induced platelet aggregation without prior addition of normal plasma to the test-tube. In conclusion the heparin fragment affected bleeding to a less extent than conventional heparin. One explanation might be a weaker inhibition of thrombin-induced platelet aggregation.