Platelet interaction with subendothelium in flowing rabbit blood: Effect of blood shear rate

An annular perfusion chamber was utilized to expose subendothelium from everted rabbit aorta to blood flowing under controlled conditions. Initial platelet contact (C), platelet spreading (S), and the formation of platelet microthrombi (T) were evaluated by a morphometric technique for exposure times ranging from 1 to 40 min and flow rates of 10, 20, 40, and 160 ml/min (comparable to vessel wall shear rates of 650, 1300, 2600, and 10,000 sec^-1). Analysis of the platelet adhesion results (C + S) with available mass transport theory indicated that, under these shear conditions, both platelet transport to the vicinity of the subendothelium and platelet reactivity with the vessel wall influenced the platelet attachment rate. At the highest shear rate studied (10,000 sec^-1) an inhibition of platelet adhesion was observed which may be due to the effect of shear on either platelet transport or reactivity. The rate of formation of platelet microthrombi increased sharply between shear rates of 650 and 1300 sec^-1 and continued to increase up to 10,000 sec^-1 even though platelet adhesion was inhibited at this shear rate. Below 1000 sec^-1 thrombi were always transiently formed, disappearing after exposure times of 20 min. Above 1000 sec^-1 platelet thrombi formed from the blood of certain experimental animals had not disappeared at exposures as long as 40 min. The mechanisms governing the inhibition of platelet adhesion and the stabilization of platelet thrombi by shear rates encountered in certain areas of the microcirculation are currently unknown.