Summary
Human endothelial cell monolayers prepared from umbilical veins have been incubated
with aspirin (1–2 mM) dissolved in Hepes modified solution and in platelet-rich plasma.
They have also been incubated with plasma prepared from subjects before and after
intake of aspirin giving a mean plasma concentration of 0.5 mM. The effects of the
endothelial cells on ADP and collagen-induced platelet aggregation and malondialdehyde
production in platelet-rich plasma have been tested. The endothelial cells had a spontaneous
inhibitory effect on all three parameters. This effect was abolished when the cells
were incubated with aspirin dissolved in MHS for 20 min and the increase in effect
observed when platelet-rich plasma was incubated with endothelial cells for a period
of 30 min was similarly inhibited when aspirin was dissolved in plasma or when plasma
prepared from subjects who had taken aspirin were used. Aspirin had no inhibitory
effect on prostacyclin (PGI2) with regard to the effect of PGI2 on platelets. On the contrary, the two compounds had an additive inhibitory effect
on platelet aggregation induced by ADP and collagen. These findings should be considered
with regard to the use of aspirin as an antithrombotic agent.
