Mechanisms of Platelet Function as Revealed by the Retention of Platelets in Glass Bead Columns*

Summary In von Willebrand's disease, the onlyin vitroabnormality of platelet function is reduced retention of platelets in glass bead columns. Although this finding suggests that the test reflects an important function in normal hemostasis, its mechanism is poorly understood. The method developed by Bowie and colleagues7has been used to elucidate some of the variables affecting the test. Heparinized blood is passed rapidly through the column and the percentage of platelets retained in the fourth and fifth ml is calculated. In normal subjects, more than 90% is usually retained. Disturbing the blood markedly decreases retention. Retention spontaneously returns to normal in about 45 minutes after disturbance or within ten minutes after addition of apyrase. Addition of 0.1 μM ADP decreases retention with a maximum effect at ten minutes. The lowered retention caused by disturbing blood appears to result from ADP probably sequestered in the platelet membrane. Slow centrifugation and remixing of blood also reduces retention which is restored by apyrase. Platelets in platelet‐rich plasma are not retained in the column even after incubation with apyrase or apyrase plus adenosine deaminase, or after adding ADP. Adding red cell ghosts to platelet‐rich plasma improves retention, although not as effectively as erythrocytes. Since ghosts contain virtually no ADP, it is suggested that they act by altering hemodynamics, either causing platelets to enter the marginal zone of plasma so that they contact the beads and tubing, or increasing the turnover of plasma in this zone to permit greater interaction of plasma components with the foreign surfaces.