PLATELET-AGGREGATION AT HIGH-SHEAR IS IMPAIRED IN PATIENTS WITH CONGENITAL-DEFECTS OF PLATELET SECRETION AND IS CORRECTED BY DDAVP - CORRELATION WITH THE BLEEDING-TIME

Techniques measuring platelet aggregation in vitro under the high shear rate conditions that can be found in the microcirculation could reflect the status of primary hemostasis better than the turbidimetric technique. We studied platelet aggregation at high shear in patients with prolonged bleeding time caused by congenital platelet secretion defects such as delta-storage pool deficiency and primary secretion defect. Two different techniques were used: shear-induced platelet aggregation in a cone-and-plate viscometer and the filter aggregation test. With both techniques, platelet aggregation at high shear rate was defective in 14 patients with delta-storage pool deficiency and in 8 with primary secretion defect. There was a statistically significant correlation between platelet aggregation at high shear rate and the bleeding time. In patients with delta-storage pool deficiency, platelet aggregation at high shear rate and the bleeding time were significantly correlated with the platelet serotonin content. The intravenous infusion of 1-deamino-8-D-arginine vasopressin (DDAVP) (0.3 micrograms/kg) increased the plasma concentration of von Willebrand factor (vWf), shortened the bleeding time, and potentiated platelet aggregation at high shear rate in all patients. Because platelet aggregation at high shear rate requires vWf, the effect of DDAVP is probably due to the induced increase in plasma vWf. Therefore, platelet aggregation at high shear rate is defective in patients with congenital defects of platelet secretion and is potentiated by DDAVP. Potentiation of platelet aggregation at high shear rate may be one mechanism by which DDAVP shortens the prolonged bleeding time of patients with congenital defects of platelet secretion.