Summary
Human umbilical vein endothelial cells in culture synthesize thromboplastin upon stimulation
with phytohaemagglutinin (PHA) or the tumor promotor 12-O-tetradecanoyl-phorbol-13-acetate
(TPA). The thromboplastin activity is further strongly enhanced in a time dependent
reaction by the presence of gel-filtered platelets or platelet aggregates. This effect
was demonstrable at platelet concentrations lower than those normally found in plasma,
it may thus be of pathophysiological relevance. The thromboplastin activity increased
with increasing number of platelets added. Cycloheximide inhibited the increase, suggesting
that de novo synthesis of the protein component of thromboplastin, apoprotein III,
is necessary.
When care was taken to remove monocytes no thromboplastin activity and no apoprotein
HI antigen could be demonstrated in suspensions of gel-filtered platelets, platelets
aggregated with thrombin or homogenized platelets when studied with a coagulation
assay and an antibody neutralization technique.
Keywords
Endothelial cells - Thromboplastin synthesis - Blood platelets - Phytohaemagglutinin
- Phorbol ester
