This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hematology and CVS, Subject name: Pharmacology
[{'content': 'Mechanism of action of atorvastatin is:- \nSelect and explain. \nA. HMG-CoA synthase stimulator, B. HMG-CoA reductase stimulator, C. HMG-CoA synthase inhibitor, D. HMG-CoA reductase inhibitor', 'role': 'user'}, {'content': 'Answer: D \nExplanation: HMG CoA reductase catalyses the rate limiting step in cholesterol biosynthesis (conversion of HMG CoA to mevalonate). Statins act by inhibiting this enzyme competitively and result in decreased cholesterol synthesis in the liver. As liver requires cholesterol for synthesis of bile acids and steroid hormones, it responds by increasing the uptake of LDL from the plasma. This is done by increasing LDL receptors on its surface. Statins are most powerful LDL lowering agents.', 'role': 'assistant'}]