This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
Platelet aggregation is caused by all, except 
Select and explain. 
A. Thromboxane A2, B. Epinephrine, C. Prostacyclin (PGI2), D. Thrombin
C: Prostacyclin (PGI2)
Answer: C: Prostacyclin (PGI2) 
Explanation: ADP, Thrombin, Epinephrine, TxA2 promote platelet aggregation whereas ADPase, NO, PGI2, PGE2 inhibit platelet aggregation. All of the aggregating agents, including thrombin, collagen, ADP, and others such as platelet-activating factor, an inside-out signaling pathway, modify the platelet surface glycoprotein complex GPIIb-IIIa (aIIbb3) so that the receptor has a higher affinity for fibrinogen or von Willebrand factor. Molecules of divalent fibrinogen or multivalent von Willebrand factor then link adjacent activated platelets to each other, forming a platelet aggregate. von Willebrand factor-mediated platelet aggregation occurs under conditions of high shear stress. Some agents, including epinephrine, serotonin, and vasopressin, exe synergistic effects with other aggregating agents.