A drug X reverses the actions produced by parasympathetic nervous system in the body but is not able to reverse the actions of exogenously administered acetylcholine in in-vitro experiments. The mechanism of drug X can be: (A) Acetylcholinesterase inhibitor, (B) Muscarinic receptor antagonist, (C) Muscarinic receptor agonsit, (D) Inhibitor of release of Ach from synaptic vesicles
Answer is D. Muscarinic receptor antagonist and agonists acts on receptor. Acetylcholine esterase inhibitor inhibits acetylcholinesterase enzyme leading to increase in the levels of acetylcholine. Inhibitor of release of acetylcholine will inhibit the release of endogenous acetylcholine from synaptic vesicles. This will not interfere with exogenously administered acetylcholine.