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': 'Nitroprusside active metabolite acts by: \nSelect and explain. \nA. Phosphokinase 1,2, B. Guanylyl cyclase, C. Phospholipase A, D. Phospholipase B', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B. Guanylyl cyclase* Nitrovasodilator (arteriodilator + venodilator)* Sodium nitroprusside is metabolized into nitric oxide, which activates guanylyl cyclase (directly or through release of NO) which leads to increase in cyclic GMP levels* Cyclic GMP activates protein kinase G which dephosphorylates MLCP (myosin light chain phosphorylase) and relaxes the smooth muscles of blood vessels* Vasodilatation occurs* Dose: 0.3mcg/kg/min* Onset of action: 30 sec* Therapeutic uses: Severe hypertension with acute myocardial infarction or left ventricular failure', 'role': 'assistant'}]