The antiplatelet aggregatory activity of Acacia nilotica is due to blockade of calcium influx through membrane calcium channels

1. The extract of Acacia nilotica (A. nilotica) blocked platelet aggregation mediated by platelet agonists, arachidonic acid (0.75 mM), ADP (4.3 μM), platelet activating factor (800 nM) and collagen (638 nM) in a dose dependent manner. 2. The extract (0.21-1.4 mg/ml) blocked the platelet aggregation induced by Ca²⁺ ionophore, A-23187 (6 μM), in a dose-dependent manner, indicating that the Ca²⁺ influx is involved in aggregation. 3. The plant extract also inhibited aggregation in platelets pretreated with phorbol, 12-myristate, 13-acetate (196 nM) alone or in combination with ADP (4.3 μM), indicating an effect on protein kinase C. 4. These results indicate that the antiplatelet aggregatory activity of the extract of A. nilotica is mainly due to blockade of Ca²⁺ channels, although evidence also suggests the involvement of protein kinase C.