Platelet Adhesion, Release and Aggregation in Flowing Blood: Effects of Surface Properties and Platelet Function.

Abstract

SummaryPlatelet adhesion to natural and artificial surfaces and adhesion-induced aggregation were investigated in vitro using an annular perfusion chamber. The surfaces were exposed to anticoagulated blood under identical flow conditions (~ arterial shear rates). The initial attachment of platelets (contact) appeared less surface specific than spreading and release. Fibrillar collagen was the most powerful inducer of platelet degranulation whereas elastin, microfibrils and epon were virtually inactive. Fibrillar collagen caused release also in the absence of spreading. Surface coverage with platelets did not exceed 25 % unless spreading occurred. Perfusion with platelet-free plasma or platelet-poor blood did not remove adhering platelets. However, platelets were translocated from mural thrombi to the surface by such perfusion. In addition, platelets which detached from mural thrombi adhered more readily to elastin or microfibrils than platelets from the circulating blood. The initial attachment of platelets to subendothelium was inhibited in von Willebrand’s disease, the Bernard-Soulier syndrome and at high concentrations of dipyridamole; spreading was inhibited in storage pool disease of rats, at low temperature (20° C), with EDTA (3 mM) and Prostaglandin E1 (1 μM); and adhesion-induced aggregation was inhibited in thrombasthenia, storage pool disease and after ingestion of sulfinpyrazone or Aspirin.It is concluded that the initial attachment (contact) of platelets, spreading and surface-induced release of platelet constituents are at least partially independent phenomena, the latter two being highly surface specific. At flow conditions which cause the disappearance of platelet thrombi, platelet adhesion appears as an irreversible process.

Axial dependence of platelet-collagen interactions in flowing blood. Upstream thrombus growth impairs downstream platelet adhesion.

“…Nonetheless, the observations support the theory of platelet depletion from the boundary layer of the blood flow, 59 an effect that is gradually overcome by increasing shear rates that enhance the radial transport of platelets toward the boundary layer and the surface, 625 and that may increase the translocation of platelet masses from upstream to downstream positions. 3 Thus, at low shear rates, the consumption of platelets by growing thrombi exceeds the radial platelet transport toward the boundary layer, while at higher shear rates the consumption is gradually compensated by the net increased flux of platelets to the boundary layer. Reduction of platelet consumption from the boundary layer by partial inhibition of thrombus growth with aspirin, which abolished the axial dependence, further substantiates the proposed physical explanation of axial-dependent platelet-surface interactions.…”

A Model Incorporating Some of the Mechanical and Biochemical Factors Underlying Clot Formation and Dissolution in Flowing Blood

“…The details surrounding the process of platelet activation, adhesion and aggregation can be found in Lasslo (1984), Yamazaki and Mustard (1987) and Anthony Ware and Coller (1995). Macroscopic studies of platelet adhesion, deposition and thrombus formation in annular flow chambers Baumgartner (1973) (or in the stagnation point flow chamber (Affeld et al (1995)) have shown that the rate and extent of platelet adhesion, platelet deposition and platelet thrombus (or mural thrombus) formation are affected by the flow conditions (shear rates) (Weiss et al, 1978;Tschopp et al, 1979;Turitto and Baumgartner, 1979;Turitto et al, 1980; see also Alevriadou et al (1993) for the effect of flow conditions on vWF mediated platelet aggregation), the presence of citrate , and surface properties (Baumgartner et al, 1976;Baumgartner, 1977; see also Hubbell and McIntire, 1986). Platelet activation itself (Kroll et al, 1996;Christodoulides et al, 1999), and sometimes lysis, is known to occur in response to prolonged exposure to high shear stresses (Wurzinger et al, 1985).…”

Quantification of fibrin deposition in flowing blood with peroxidase-labeled fibrinogen. High shear rates induce decreased fibrin deposition and appearance of fibrin monomers.

“…The presence of fibrin is usually demonstrated by immunofluorescence with the use of radioisotopes or by morphological quantification. 12 -15 Fibrin deposition on subendothelium in flowing blood has been studied in an ex vivo thrombosis model originally developed by Baumgartner et al 3 - 16 - 19 To study the participation of the vessel wall in thrombus formation, our laboratory recently introduced an adapted in vitro thrombosis model that permits studies of thrombus formation in flowing blood on extracellular matrixes of cultured human cells. 20 In both models, the morphometric evaluation of fibrin deposition led to semiquantitative results at best.…”

“…Fibrin dep-L osition and platelet aggregation are essential steps in thrombus formation on subendothelial surfaces or perivascular connective tissue. 1 " 3 To what extent fibrin deposition contributes to the formation of the thrombus is influenced by several parameters such as the availability of tissue factor on the vascular surface and local flow characteristics. 4 -5 Fibrin accounts for most of the mass of thrombi found in large veins; such thrombi mainly consist of fibrin and red blood cells.…”