Which one of the following is released by blood platelets during haemorrhage to produce vasoconstriction?

The initial event is constriction of the vessel and formation of a temporary hemostatic plug of platelets that is triggered when platelets bind to collagen and aggregateThis is followed by conversion of the plug into the definitive clotThe constriction of an injured aeriole or small aery may be so marked that its lumen is obliterated, at least temporarily.The vasoconstriction is due to serotonin liberated from platelets that adhere to the walls of the damaged vesselsRef: Ganong's Review of Medical Physiology Twenty-Third Edition Page No: 531