Protamine enhances fibrinolysis by decreasing clot strength: role of tissue factor-initiated thrombin generation.
BACKGROUND
Excessive protamine administration to neutralize heparin after cardiopulmonary bypass has been implicated as a cause of postoperative hemorrhage. Protamine directly inhibits thrombin and tissue factor (TF)-mediated activation of factor VII. However, the half-life of protamine is only 4.5 minutes; thus the purpose of this study was to determine if protamine could enhance fibrinolysis, explaining the delayed, protamine-associated hemorrhage observed in the postoperative period.


METHODS
Human plasma containing 0, 6.25, 12.5, or 25 microg/mL of protamine (n = 6 per condition) was exposed to 0.01% tissue factor and tissue-type plasminogen activator (tPA, 100 U/mL) for 30 minutes, with clot growth and disintegration measured by Thromboelastograph (Haemoscope Corp, Skokie, IL). The TF was increased to 0.1% in additional experiments with plasma containing protamine (25 microg/mL) and tPA.


RESULTS
Protamine significantly (p < 0.05) delayed the time to clot initiation, decreased the speed of clot propagation, and diminished clot strength in a concentration-dependent fashion. The onset of fibrinolysis was significantly (p < 0.05) increased only in samples with 25 microg/mL of protamine, and the rate of clot lysis was not different among the conditions. The clot duration time (from initiation to disintegration) was significantly (p < 0.05) decreased in a concentration-dependent manner by protamine. Increased TF concentration (0.1%) significantly improved clot growth kinetics and prolonged clot duration in samples with 25 microg/mL of protamine compared with samples activated with 0.01% TF.


CONCLUSIONS
Protamine enhanced fibrinolysis by decreasing clot strength by diminishing TF-initiated thrombin generation. Additional, clinical investigation is warranted to mechanistically implicate protamine-mediated enhancement of fibrinolysis to delayed bleeding after cardiopulmonary bypass.
Nielsen
Vance G
VG
Department of Anesthesiology, The University of Alabama, Birmingham, Alabama 35249-6810, USA. vnielsen@uab.edu
D001777:Blood Coagulation / Q000502:physiology*; D007692:Diatomaceous Earth; D005342:Fibrinolysis / Q000187:drug effects*; D006494:Heparin Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D010949:Plasma / Q000502:physiology; D011479:Protamines / Q000008:administration & dosage / Q000494:pharmacology*; D013916:Thrombelastography; D013917:Thrombin / Q000032:analysis*; D013925:Thromboplastin / Q000502:physiology*
D006494:Heparin Antagonists; D011479:Protamines; D007692:Diatomaceous Earth; D013925:Thromboplastin; D013917:Thrombin