Summary
The assumption that fibrin and crosslinked fibrin impart irreversibility to arterial
thrombi is explored with procedure developed for measuring changes in platelet function,
morphology and fibrinogen metabolism in aging occlusive thrombi, in which the condition
of stasis is imposed uniformly. Arterial thrombi containing autologous 111In labeled platelets were generated in vivo by bilateral mechanical injury of porcine carotid arteries. Vessels containing the
platelet-rich thrombi were harvested and incubated intact (37° C) for intervals ranging
from 30 min to 12 h. The isolated vessels were then bisected and agitated in culture
medium containing tick anticoagulant and hirudin for 60 min. Disaggregated platelets
were evaluated for yield (from 111In radioactivity) viability (dense body ATP secretion)
and morphology (electron microscopy). Western analysis of fibrin(ogen) in thrombus
extracts was performed using anti-fibrinogen Bβ- and γ-chain monoclonal antibodies
for thrombi at each time point. A stable recovery of nearly 50% of platelets was observed
during 12 h of thrombus aging. As thrombi aged, viability of disaggregated platelets
gradually decreased with platelet necrosis the predominant feature beyond 6 h. By
western analysis of thrombus extracts, nearly 50% of fibrinogen was cleaved to fibrin
and extensively crosslinked within 30 min of injury with no evidence of fibrinolysis.
With the exception of a declining proportion of γ-monomer, these features remain relatively
constant during 12 h of thrombus maturation. It is concluded that neither fibrin nor
crosslinked fibrin are dominant factors imparting cohesion within platelet thrombi.
Furthermore, under conditions of complete arterial occlusion imposed by this experimental
design, there is no evidence of endogenous fibrinolysis.
Keywords
Fibrin - crosslinked fibrin - fibrinolysis - platelets - arterial thrombosis
