Which of the following prevents platelet aggregation?

Prostacyclin plays a key role in the regulation of platelet function and serves as a potent inhibitor of platelet aggregation. It is produced by endothelial cells and acts on the vascular smooth muscle to induce vasodilation. This compound works by binding to specific receptors on platelets, leading to an increase in cyclic adenosine monophosphate (cAMP) levels. Elevated cAMP levels result in the inhibition of the activation processes that facilitate platelet aggregation, ultimately reducing the ability of platelets to clump together.

In contrast, Thromboxane A2 is a pro-aggregatory substance released by activated platelets, promoting aggregation and vasoconstriction. While Thromboxane B2 is a stable metabolite of Thromboxane A2 and does not possess platelet-activating properties, it does not inhibit aggregation either. Antithrombin is a natural anticoagulant that inhibits several enzymes in the coagulation cascade, but it does not specifically prevent platelet aggregation. Thus, prostacyclin is uniquely positioned as the primary compound within this context that effectively prevents platelet aggregation.