Drugs of the Parasympathetic NS

Drugs of the Parasympathetic NS

1. Cholinergics/Parasympathomimetics: Stimulate the parasympathetic NS

   • Rest and digest response
   • Direct acting: Bind to cholinergic receptors to produce rest and digest resposne
     • Relatively resistent to achetylcholenesterase, so they last longer than Ach
     • Poorly absorbed in Gi tract, do not cross blood-brain barrier
     • Also called muscarinic agonists
   • Indirect acting: Inhibit action of AchE, allowing endogenous Ach to avoid rapid destruction and bind with cholinergic receptors for longer
     • Also called cholinesterase inhibitors
     • Affects a lot more sites.
   • Very few of these are widely used because of high potential for serious adverse effects
     • Some are used for affect on skeletal muscle (see pg. 135)
     • Can cause a cholinergic crisis

2. Cholinergic blocking/Anticholinergics: Inhibits the parasympathetic nervous systm

   • Fight or flight respose
   • Called muscarinic antagonists b/c they're selective for Ach muscarinic receptors
   • Competes with Ach for binding with muscarinic receptors,
     • Causes sympathetic NS actions to dominate
   • Relatively high incidence of side effects