Vagal stimulation causes bradycardia, which can be blocked by: (A) atenolol, (B) atropine, (C) doxazosin, (D) phenylephrine
Answer is B. 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.