A 25-year-old machinist is injured by a metal sliver in his left hand. Over the next few days, the wounded area becomes reddened, tender, swollen, and feels warm to the touch. The patient goes to the emergency room to have the sliver removed. Twenty-four hours later, endothelial cells at the site of injury in the patient release a chemical mediator that inhibits further platelet aggregation. Name this mediator of inflammation.

Prostaglandin (PGI2 ). PGI2 is a derivative of arachidonic acid that is formed in the cyclooxygenase enzyme pathway. It promotes vasodilation and bronchodilation and also inhibits platelet aggregation. It activates adenylyl cyclase and increases intracellular levels of cAMP. Its action is diametrically opposite to that of thromboxane A2 (choice E), which activates guanylyl cyclase and increases intracellular levels of cGMP. Plasmin (choice A) degrades fibrin. Serotonin (choice C) is a vasoactive amine. Thrombin (choice D) is a protease that mediates the conversion of fibrinogen to fibrin.Diagnosis: Acute inflammation