plateletactivating

Platelet activating is a descriptor used for substances, signals, or conditions that stimulate platelets to respond, initiating the process of activation. Platelet activation is central to hemostasis and thrombosis; it involves changing shape, releasing granule contents, and enabling platelet aggregation to form a clot.

Common pathways: Activation is mediated by receptors on the platelet surface that respond to agonists such as thrombin, ADP, collagen, ristocetin, and thromboxane A2. Thrombin engages PAR receptors, ADP via P2Y1/P2Y12, collagen through GPVI and integrins, TXA2 through the TP receptor, and vWF via GPIb-IX-V under high shear.

Consequences: Activated platelets express activated integrin αIIbβ3, secrete pro-aggregatory mediators, and expose P-selectin; they recruit additional platelets and support fibrin formation.

Platelet activating substances include platelet-activating factor (PAF), a potent phospholipid mediator that acts through the PAF receptor to promote aggregation; other triggers include cytokines and immune complexes in inflammatory states.

Clinical and research relevance: Assessing platelet activation can be done with aggregometry, flow cytometry for activation markers, or thromboelastography. Abnormal platelet activation contributes to bleeding disorders when insufficient and to thrombotic diseases when excessive; antiplatelet therapies target these pathways to reduce cardiovascular risk.