Low-affinity heparin potentiates the action of high-affinity heparin oligosaccharides.

Previous studies have shown that high-affinity (HA) heparin oligosaccharides, with molecular weights of 3,000-5,000, were less effective than unfractionated heparin in preventing serum-induced venous thrombosis in rabbits, using a Wessler stasis model. In the present study, a larger high-affinity fragment (M.Wt. 6,000-6,500) was also found to be less effective than unfractionated heparin as an antithrombotic agent. However, addition of 80 micrograms/kg low affinity (LA) heparin to 80 micrograms/kg of this HA fragment significantly potentiated its antithrombotic activity, and the antithrombotic action of the mixture was equivalent to that of unfractionated heparin. Significant potentiation of antithrombotic activity was also observed on the addition of LA heparin to a HA decasaccharide (M.Wt. 3,000-3,500) with anticoagulant activity only against Factor Xa. The LA heparin content of low molecular weight heparin fractions appears to be an important determinant of their antithrombotic activity.