In vitro measurement of platelet adhesion to intact endothelial cells under low shear conditions

BACKGROUND: Prediction of thrombus formation at intact arterial walls under low shear flow conditions is clinically important particularly for better prognoses of embolisation in cerebral aneurysms. Although a new mathematical model for this purpose is necessary, little quantitative information has been known about platelet adhesion to intact endothelial cells. OBJECTIVE: The objective of this study is to measure the number of platelets adhering to intact endothelial cells with a focus upon the influence of the shear rate. METHODS: Endothelial cells disseminated in mu-slides were exposed to swine whole blood at different shear rates. Adenosine diphosphate (ADP) was used as an agonist. Adherent platelets were counted by means of scanning electron microscopy. RESULTS: At an ADP concentration of 1 mu M, 20.8 +/- 3.1 platelets per 900 mu m(2) were observed after 30-minute perfusion at a shear rate of 0.8 s(-1) whereas only 3.0 +/- 1.4 per 900 mu m(2) at 16.8 s(-1). CONCLUSIONS: The number of adherent platelets is determined by a balance between the shear and the degree of stimulation by the agonist. At an ADP concentration of 1 mu M, a limit to the shear rate at which platelets can adhere to intact endothelial cells is considered to be slightly higher than 16.8 s(-1).