Summary
The effects of GPIIb/IIIa blockade on clot retraction were studied utilizing an instrument
which directly measures force produced by platelets. GPIIb/IIIa disruption by calcium
chelation, and GPIIb/IIIa blockade by peptides and anti-GPIIb/IIIa antibodies were
investigated. One mM EDTA suppressed ADP-induced platelet aggregation by 72% and reduced
force developed at 1200 s by 33%. At 234 μM, the tetrapeptide Arg-Gly-Asp-Ser (RGDS)
suppressed platelet aggregation by 74%, reduced force at 1200 s by 45% and reduced
gel elastic modulus by 19%. At 10 μM, the peptide D-Arg-Gly-L-Asp-L-Try (D-RGDW) completely
suppressed platelet aggregation, reduced force development by 38% and reduced gel
elastic modulus by 29%. At 0.133 μM, monoclonal anti-GPIIIa antibody (AP-3) reduced
force development by 74% and reduced gel modulus by 60%. Murine antiGPIIb/IIIa antibodies
10E5 and 7E3 markedly suppressed force development. At 0.133 μM, 10E5 reduced force
by 89% and reduced gel modulus by 67%. At 0.053 μM, 7E3 completely stopped force development
and reduced gel modulus by 46%. Platelet aggregation was blocked by 0.027 μM 7E3.
Selective GPIIb blockade by antibodies did not affect force development. None of the
agents studied altered fibrin structure as monitored by effects on fibrin mass/length
ratios. Suppression of platelet aggregation occurred at inhibitor concentrations substantially
lower than those required to suppress force development. Complete suppression of platelet
aggregation did not assure inhibition of clot retraction probably due to profound
platelet activation by thrombin. These results indicate that inhibition of fibrin(ogen)
binding to GPIIb/IIIa, either by disruption of GPIIb/IIIa or by competitive blockade,
inhibits platelet mediated force development and results in clot structures which
are substantially less resistant to deformation by outside forces.
