Activation Of Hageman Factor By Heparin

Exposure of plasma to certain negatively charged substances, leads through the action of activated Hageman factor (HF) to generation of bradykinin (bk), a peptide cleaved from HMW-kininogen by kallikrein. We designed a method which permits rapid measurement of plasma Bk by RIA. This method provides a specific and sensitive means to study contact activation in whole blood and plasma. Heparin (Hep) was found to be effective in the activation of HF even at low concentrations (1,25 U/ml plasma). The rate of activation was dependant on the mol. weight of the Hep studied. Upon incubation of HF deficient plasmas with high concentrations of Hep (20 U/ml), no Bk generation was observed. The capacity of Hep to induce Bk-generation in different normal plasmas varied considerably. Upon incubation of plasma from 8 individuals with Hep (5 U/ml) at 0’C for 2 h, the increase of the Bk concentrations ranged from 20 to 770 ng/ml plasma. Evidence was obtained that “cold promoted activation” (CPA) accounted for these differencies. When CPA-positive plasmas (as judged by shortening oF the thrombotesttime after incubation overnight at 4’C) were incubated with Hep (5 U/ml) for 2 h at 0’C, the Bk-concent rat ions increased from 1 to 375 ± 75 ng/ml (mean ± SEM), wheras in the absence of Hep less than 10 ng Bk/ml/2h was generated. However, when CPAnegative plasmas were incubated with Hep, the increment of Bk was only 25 ± 20 ng/ml 2h. We assume that Hep and the active principle present in CPA positive plasma act synergetically in HF activation. Similarly, the action of dextran sulphate (DS) on HF was potentiated by Hep. When plasma (CPA negative) was incubated with either low concentrations of DS (<1 μg/ml) or Hep (2-5 U/ml), only minor amounts of BK were generated. When Hep and DS were added together to plasma, the amount of Bk generated increased up to 50-fold under these conditions. We conclude that in plasma, heparin is an activator of HF, notably in the presence of other activators of the contact system.