This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Pharmacology
[{'content': 'What is the important action of nitrates in angina? \nSelect and explain. \nA. Coronary vasodilation, B. Decreases preload, C. Decreases afterload, D. Decreases heart rate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B. Decreases preloadNitrates cause release of nitric oxide which causes activation of guanylyl cyclase and through series of steps (via activation of protein kinase and phosphatases) activate myosin light chain through dephosphorylation which causes smooth muscle relaxation and hence vasodilatation. This decreases systemic vascular resistance and there will be increased pooling of blood. All of these events can lead to decrease in preload.', 'role': 'assistant'}]