Cholinergic stimulation of the GI tract and uterus depends on activating muscarinic receptors to increase smooth muscle motility and contractions. Carbamylcholine (carbachol) is a direct cholinergic agonist that acts on both muscarinic and nicotinic receptors and, importantly, is relatively resistant to acetylcholinesterase, giving a longer duration of action. This combination makes it effective at promoting GI motility and uterine contractions in swine. Bethanechol is muscarinic-selective and can stimulate GI motility, but it lacks the nicotinic component that can enhance overall smooth muscle responsiveness, and in swine the preferred agent for uterine stimulation can be carbamylcholine. Pilocarpine is mainly used for muscarinic effects in the eye and salivation, not for GI atony or labor induction. Neostigmine increases acetylcholine levels indirectly by inhibiting acetylcholinesterase, but its broad activity and longer systemic effects make it less specific for these swine indications.