Bethanechol is a muscarinic cholinergic antagonist with no action on nicotinic ACh receptors. Bethanechol is commonly used to treat urinary retention by activating bladder smooth muscle via M3 Gq receptors that function by increasing phospholipase C conversion of PIP2 (phosphoinositide) to IP3 and DAG (FA2020 p240, p237, p238).

Wrong answers:

• Atropine is a muscarinic antagonist which would non increase phosphoinositide turnover but decrease it (FA2020 p241)
• Neostigmine is an indirect cholinergic agonist that works by inhibiting acetylcholinesterase that does work at the muscarinic synapse as well and is used for myasthenia gravis as well as postoperative ileus and urinary retention
• Succinylcholine is a depolarizing muscarinic agonistnthat causes sustained depolarization and prevents contraction, used as a paralytic in anesthesia (FA2020 p551)
• Trimethaphan is a drug that counteracts cholinergic transmission at the nicotinic receptors of the autonomic ganglia and therefore blocks both the sympathetic nervous system and the parasympathetic nervous system. It is used to treat hypertension