7. Pharmacology of the autonomic nervous system: Pharmacology of the parasympathetic nervous system (parasympathomimetics, parasympatholytics) Flashcards
Parasympathetic nervous system
Rest & Digest
Parasympathomimetics
Stimulants
- Cholinergic drugs (those resembling ACh)
Parasympathomimetic effect: Eye
- Iris contraction
- ↑outflow from canals of Schlemm
- ↓intraocular pressure
- ↑secretion of tears
- Myosis (excess pupil constriction)
Parasympathomimetic effect: Cardiovascular system
- Negative chronotropic effect = ↓SA node activity
- Negative dromotropic effect = ↓conduction velocity through AV node
Parasympathomimetic effect: GI tract
- ↑ SM contraction & tone, peristaltic activity & motility
- ↑ Salivation & stomach acid secretion
- Vomiting, diarrhea
Parasympathomimetic effect: respiratory tract
Bronchoconstriction & ↑ bronchial secretions
Parasympathomimetic effect: Urinary tract
- Ureter & bladder SM contractinon
- Relaxation of sphincter muscle
Direct parasympathomimetics
Act by stimulating nicotinic or muscarinic receptors
- ACh
- Carbachol
- Pilocarpine
List some direct parasympathomimetics
- Acetylcholine
- Carbachol
- Pilocarpine
Carbachol
- Nonspecific to M-ACh receptors
- Used locally in metritis & as eye drops in glaucoma therapy
Pilocarpine
- Glaucoma therapy
- Keratoconjunctivitis sicca
Indirect parasympathomimetics
Act by inhibiting cholinesterase, promoting ACh release
List some indirect parasympathomimetics
- Neostigmine
- Pyridostigmine
- Edrophonium
- Organophosphates
Neostigmine
Eye-drop for treatment of glaucoma
- IV/IM for myasthenia gravis & intestinal motility ↑
Pyridostigmine
PO for myasthenia gravis & ↑ intestinal motility
Edrophonium
Myasthenia gravis diagnosis = Tensilon test
Organophosphates
Irreversible inhibitors of AChE ectoparasiticides
Antidotes: Atropine, pralidoxime
Parasympatholytics
Anticholinergic drugs
Muscarinic receptor antagonists
Parasympatholytic effect: Eye
Mydriasis
m. constrictor pupillae inhibition
Parasympatholytic effect: Cardiovascular system
Lifting cholinergic blockade of heart → Tachycardia
Parasympatholytic effect: GI tract
- Hyposalivation
- ↑ Transit time
- Constipation
- Inhibition of:
- Peristalsis
- Segmental contractions
Parasympatholytic effect: Respiratory Tract
Bronchodilation
List some parasympatholytics
- Atropine
- Glycopyrrolate
- Homatropine
- Ipratropium
- Benzethimid
Atropine
Highly toxic
- Atropa belladonna
- Crosses BBB
- Rabbits are relatively resistant
- Liver atropinase
Glycopyrrolate
- Low BBB penetration
- Premedication
Homatropine
Diagnostic eye examination
Ipratropium
- Low BBB penetration
- COPD
- Feline asthma
Benzethimid
Antidiarrheal
