Thromboxane A, is produced mainly by

Platelet Activating Factor(PAF) secreted by platelets act G protein-coupled receptor to produce arachidonic acid derivative like Thromboxane A2 Ref: Ganong's Review of Medical Physiology Twenty-Third Edition pg no:75 Thromboxane A2 is produced by activated platelets during hemostasis and has prothrombotic activity. It activates new platelets and increase platelet aggregation.