Summary
Amounts of human brain thromboplastin that do not stimulate thrombin generation in
platelet poor plasma, were shown to advance by about 4 min an explosive formation
of thrombin that occurs after recalcification in the presence of blood platelets.
This synergistic effect is inhibited by the specific thrombin inhibitor hirudin and
mimicked by adding low concentrations (< 5 nM) of thrombin to platelet rich plasma.
It is our conclusion that, small amounts of thrombin, generated under the influence
of thromboplastin induced procoagulant activity in the blood platelets. This activity
is most likely mainly due to procoagulant phospholipids. Heparin inhibits this effect
and retards the explosive thrombin formation. It does not, however, diminish the peak
amount of thrombin eventually formed, because heparin neutralizing material released
from the activated platelets quenches the heparin effect.
Key words
Platelets - Tissue factor - Thrombin - Heparin
