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
At low infusion rates of 3-5 mcg/kg/min, what action is produced by dopamine? 
Select and explain. 
A. Vasoconstriction, B. Increased renal blood flow, C. Increased cardiac contractility, D. Decreased blood pressure
B: Increased renal blood flow
Answer: B: Increased renal blood flow 
Explanation: Ans: B. Increased renal blood flow(Ref: Goodman Gilman 12/e p355; KDT 7/e p134. 6/e p507)Action of dopamine:At low concentrations (2 to 5 mcg/kg per minute):Primarily acts on vascular D1 receptors.Mainly renal, mesenteric & coronary beds.By activating adenylyl cyclase a raising intracellular cyclic AMP concentrations.D1 receptor stimulation a Vasodilation.Increases in glomerular filtration rate, renal blood flow & Nat+ K+ - ATPase pump.