The effect of oscillatory flow on the release reaction and aggregation of human platelets.

Abstract The effect of variable shear rate on the thrombin-induced release of [ 14 C]serotonin from human platelets was investigated by subjecting washed suspensions containing 5 × 10 5 cells/μl to laminar oscillatory flow at 37°C in 1-meter lengths of 1.57-mm polyethylene tubing. The suspensions were prepared at 37°C in Tyrodes-albumin containing apyrase to avoid desensitization of the platelets by released ADP. After flow, the sheared sample and a control, incubated at rest at 37°C, were stirred with thrombin at concentrations of 0.04 units/ml (threshold at which aggregation just occurred) and 0.02 units/ml, and the 14 C-activity in the supernatant measured after centrifugation. At time-averaged wall shear rates G (R 0 ) = 2350 sec −1 and 20 min shear, there was no significant release of [ 14 C]serotonin due to flow alone. However, in 53 experimental runs the mean release at 0.02 and 0.04 units/ml exceeded that in the paired controls by 6.1%(±1.4%, SE) and 10.1%(±1.3%) of the total activity in the suspension. The increase in serotonin release was not significant at G (R 0 ) sec −1 . The synergistic effects of flow were also noted when [Ca 2+ ] was increased from 4 to 12 mEq, and in the presence of ASA (1 mg/ml), release being less inhibited in the sheared samples. When adrenaline (2.5 μM ) was added, the serotonin release, which increased by 26.4%(±3.8%) in 17 controls at the lower thrombin level, was further enhanced by 10.9%(±2.6%) in the paired sheared samples. However, when adrenaline was added after oscillatory flow, the reverse occurred, the sheared samples releasing 8.5% less than the controls. Studies in the aggregometer showed that the rate and extent of aggregation in the sheared samples was a little lower than that in the controls.