This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemical mediators in plasma: Kinin system, Subject name: Pathology
[{'content': 'A 59-year-old man experiences acute chest pain and is rushed to the emergency room. Laboratory studies and ECG demonstrate an acute myocardial infarction; however, coronary aery angiography performed 2 hours later does not show evidence of thrombosis. Which of the following mediators of inflammation causes relaxation of vascular smooth muscle cells and vasodilation of aerioles at the site of myocardial infarction in this patient ? \nSelect and explain. \nA. Bradykinin, B. Histamine, C. Leukotrienes, D. Nitric oxide', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Nitric oxide (NO), which was previously known as endothelium-derived relaxing factor, leads to relaxation of vascular smooth muscle cells and vasodilation of aerioles. NO also inhibits platelet aggregation and mediates the killing of bacteria and tumor cells by macrophages. Histamine , leukotrienes and thromboxane A2 stimulate the contraction of smooth muscle cells.', 'role': 'assistant'}]