Summary
Fibrinogen is a cofactor in the aggregation of human platelets and must be added to
suspensions of washed human platelets forextensive aggregation to occur in response
to ADR Although thepatterns of fibrinogen binding and dissociation during plateletaggregation
and deaggregation are similar for human and rabbitplatelets, washed rabbit platelets
aggregate extensively whenstimulated with ADP even in the absence of added fibrinogen.
Todetermine whether secreted fibrinogen was present on the surfaceof ADP-stimulated
platelets and available to support aggregation, the binding of 125I-F(ab’)2 fragments of anti-fibrinogen antibodiesto formaldehyde-fixed platelets was measured.
Although nofibrinogen was detected on human platelets either before or aftertreatment
with ADP, fibrinogen was expressed on the surface ofrabbit platelets after stimulation
with ADP. However, thissecreted fibrinogen did not dissociate during deaggregation
of theplatelets. Thus, the aggregation of rabbit platelets in the absenceof exogeneous
fibrinogen may be supported by secreted fibrino-gen, but a fibrinogen-independent
component has not beencompletely ruled out.
Keywords
Human platelets - Rabbit platelets - Fibrinogen - ADP
