This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Mechanism of action of nifedipine is: \nSelect and explain. \nA. It has a prominent smooth muscle relaxant action causes arteriolar dilation leading to fall in blood pressure, B. Nifedipine depresses the SA node thus decreasing myocardial excitability, C. Mainly depression of A-V conduction, D. Decrease cardiac output thus decreasing load on myocardium', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Nifedipine It is the first and the prototype\xa0DHP, but infrequently used now. The overriding\xa0action is arteriolar dilatation → t.p.r. decreases,\xa0BP falls. The direct depressant action on heart\xa0is significant. As described above,\xa0it does not\xa0depress SA node or A-V conduction. Nifedipine\xa0acts rapidly, due to which reflex sympathetic\xa0stimulation of heart predominates producing tachycardia, increased contractility and CO. No\xa0decrease in venous return along with lowering\xa0of afterload aids increase in CO. Coronary flow\xa0is increased. The duration of action is short\xa0(3-6 hours).\nDose: 5-20 mg BD-TDS oral.\nt.p.r = total peripheral resistance.\nCO =\xa0Cardiac output.\nReference: Essentials of Medical Pharmacology Eighth Edition KD\xa0 TRIPATHI\xa0 page no 595', 'role': 'assistant'}]