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AC Cox, P Inyangetor, CT Esmon and BN White
Platelets provide a procoagulant activity for the conversion of prothrombin
to thrombin during normal hemostatis. This activity designated as platelet
prothrombin-converting activity (PPCA) was monitored as rate of thrombin
production in a two-stage assay using gel- filtered bovine platelets,
factor Xa, and prothrombin. Expression of PPCA was not associated with
ADP-induced release or platelet shape change but was associated with
aggregation. Release of the contents of dense bodies, measured by release
of 14C-5-hydroxytryptamine, was not required for expression of PPCA during
platelet aggregation. During the PPCA assay, 5-hydroxytrypamine was
released, but only after onset of thrombin production. Furthermore, the
release of 5-hydroxytryptamine was retarded during the assay by the
addition of 2 mM theophylline and 100 nM prostaglandin E1 without a
comparable reduction in PPCA. In addition, 125I-factor-Xa was bound in
greater amounts to platelets (aspirin-treated) after ADP-induced
aggregation (without detectable release) than to unactivated control
platelets. Finally, the PPCA of the ADP-activated platelets was saturated
with respect to factors Xa and Va at less than 1 nM concentrations,
indicating that the aggregation induced by ADP leads to the exposure of
specific procoagulant sites by some process other than dense body
secretion.
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| Copyright © 1979 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
