SHEAR-INDUCED PLATELET ACTIVATION AND PLATELET MICROPARTICLE FORMATION AT BLOOD-FLOW CONDITIONS AS IN ARTERIES WITH A SEVERE STENOSIS

In the present study, we investigated whether high arterial shear stre sses at various exposure times or a sudden increase in shear stress in troduced by a stenosis affect platelet activation and platelet micropa rticle formation in native human blood. We used a parallel-plate perfu sion chamber device through which nonanticoagulated human blood was dr awn (10 mL/min) by a pump directly from an antecubital vein through th e flow channel of a perfusion chamber at wall shear rates of 420, 2600 , and 10 500 s(-1). In another set of experiments, an eccentric stenos is was introduced into the flow channel. Wall shear rates of 2600 or 1 0 500 s(-1) at the stenosis apex were maintained at the same flow rate . The wall shear rate upstream and downstream of these stenoses was 42 0 s(-1). A shear rate of 420 s(-1) is within the range of those encoun tered in healthy small coronary arteries, whereas those of 2600 and 10 500 s(-1) are representative for vessels with various degrees of sten otic lesions. The blood was exposed to these shear rates for periods v arying from 0.075 to 3.045 seconds. Platelet activation was assessed a s activated glycoprotein (GP) IIb/IIIa by FITC-labeled monoclonal anti body (MAb) PAC-1 and aminophospholipid translocation by FITC-labeled a nnexin V. Microparticle formation was quantified by FITC-labeled MAb Y 2/51 directed against GP IIIa. Significant platelet activation and for mation of microparticles were observed at 10 500 s(-1) only (P<.008). This shear-induced platelet activation and microparticle formation wer e enhanced by introduction of a thrombus-promoting surface consisting of type III human collagen fibrils. Introduction of the most severe st enosis at 10 500 s(-1) further increased platelet activation (P<.017). The collagen-induced thrombus formation increased the platelet thromb us volume at 10 500 s(-1) from 16.5 to 33.8 mu m(3)/mu m(2) (P<.003) o n the stenosis apex when the most severe stenosis was used. A correlat ion (P<.0001) between platelet thrombus volume and platelet microparti cle formation was observed in the presence of the eccentric stenoses. Apparently, high shear stress (315 dynes/cm(2) at 10 500 s(-1)), as en countered in severe atherosclerotic arteries, activated platelets and triggered platelet microparticle formation. In contrast, no significan t platelet activation or formation of platelet microparticles was obse rved at physiological shear (420 s(-1)) or at the shear condition simu lating shear in arteries with a less severe stenosis (2600 s(-1)). The data imply that platelets are activated and form microparticles in na tive blood at very high shear stresses. These events are potentiated b y prolonged exposure to the high shear or by a sudden change of increa sing shear due to the stenosis. The latter situation apparently enhanc es platelet thrombus formation at the stenosis.