This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: A.N.S., Subject name: Pharmacology
Vagal stimulation causes bradycardia, which can be blocked by 
Select and explain. 
A. atenolol, B. atropine, C. doxazosin, D. phenylephrine
B: atropine
Answer: B: atropine 
Explanation: Bradycardia due to vagal stimulation is elicited by activation of muscarinic receptor in the heart. Atropine, which is an antagonist at M receptors, blocks bradycardia elicited by stimulation of the vagus, including reflex bradycardia due to increases in mean BP caused by vasoconstrictors.