Inhibition of Thrombin Induced Aggregation of Human Platelets by Heparin

Washed human platelets were aggregated by heparin in the presence of divalent cations. Heparin inhibited the thrombin induced platelet aggregation and release of platelet adenine nucleotides. The inhibition was maximal at low thrombin concentrations, and increased with increasing heparin concentrations. The inhibition was immediate and reversible. Protamine and polybrene per se inhibited the aggregation induced by thrombin.