A vasodilator released during fibrinolysis that reverses platelet effects is:

Nitric oxide (NO) is a key vasodilator released during fibrinolysis that counteracts platelet aggregation and promotes vasodilation to restore normal blood flow once clot dissolution is underway. Produced by vascular endothelial cells, NO activates guanylyl cyclase in smooth muscle and platelets, raising cyclic GMP levels, which causes smooth muscle relaxation (vasodilation) and inhibits platelet activation and aggregation. This reversal of platelet effects is essential to prevent excessive or ongoing thrombus formation after the injured vessel has been repaired. Dopamine is a catecholamine neurotransmitter and renal vasodilator but is not specifically released during fibrinolysis to reverse platelet effects. Histamine is a mediator released from mast cells and basophils during allergic and inflammatory responses, causing vasodilation and increased vascular permeability, but it is not characteristically part of the fibrinolytic phase. Bradykinin is a potent vasodilator and pain mediator generated in the kinin system and can inhibit platelet aggregation, but it is not the primary vasodilator released specifically during fibrinolysis to reverse platelet effects. Nitric oxide fits most precisely because it is produced by endothelium in direct response to fibrinolytic activity and the need to restore vascular homeostasis.