ABNORMALITIES OF PLATELET AGGREGATION AND ENHANCED FACTOR X ACTIVATOR ACTIVITY OF WASHED PLATELETS IN SICKLE CELL DISEASE

The occurence of microvascular occlusion is one of the most prominent pathologic features of sickle cell anemia. The mechanism of vaso occlusion has generally been attributed to the abnormal shape and reduced deformability of the sickled erithrocy tes. However, the involvement of vascular endothelium, platelets and their interactions with coagulation factors may also be of pathogenic significance in microvascular occlusive crises.

We investigated the interaction between vascular endothelium, platelets and blood coagulation factors in 23 patients with Sickle Cell Disease (SCD) and in normal volunteers.

Factor X activator activity in washed platelets was performed according to Semeraro and Vermylen (1977), thromboxane B₂ (TXB₂) and 6-keto-PGF₁β were determined using specific radioimmunoassays.. PAF-acether from platelets was determined according to Chignard et al (Nature, 1979, 279:799). Platelet aggregation was performed with a Chrono-Log Aggregometer (Model 440) on platelet rich plasma (PRP) using the Born method. Prostacyclin release from endothelium was performed according to Mon-cada et al (Lancet i:18, 1977).

Our results showed that platelets from patients with SCD ha ve enhanced factor X activator activity (p < 0.0001), produce mo re PAF-acether than controls (p < 0.02) and showed hyperaggregability in these patients as compared to normal volunteers (p < 0.00001).

We concluded that platelets from homozygous sicklers have enhanced factor X activator activity as well as increased capacity for PAF-acether production. These abnormalities may contribute to the incidence of vaso occlusive crises in these patients.