Cholinergics Flashcards
M1 effects
‘neural’, slow excitation of ganglia
M2 effects
‘cardiac’, decrease in rate and force of contraction (mainly of atria), mediation of presynaptic inhibition
M3 effects
‘glandular’, cause secretions, contraction of visceral smooth muscle, vascular relaxation
Where are nAChRs found?
At the ganglia and at skeletal muscle (voluntary muscle)
What are antagonists of nAChRs?
Hexamethonium (acting at ganglia), tubocurarine (at NMJ)
Other NMJ blockers - pancuronium, vecuronium, atracurium, mivacurium, suxamethonium
nAChR agonists?
Nicotine…
What is an example of a depolarising blocking agent?
Suxamethonium
What is a depolarisation block?
It occurs at when the excitatory nAChRs are persistently activated. Its depolarising action lasts long enough to cause the endplate region to be inexcitable. It is quickly hydrolysed by ChE. If ChE is blocked, circulating [ACh] can become enough to cause a depolarisation block.
What are the dangers of suxamethonium?
Bradycardia;
potassium release (can cause hyperkalaemia and therefore ventricular dysrhythmia/cardiac arrest in individuals who have experienced trauma/burns); increased intraocular pressure;
prolonged paralysis in individuals who have ChE-deficiency (due to several reasons);
malignant hyperthermia - rare…
Muscarinic agonists?
Bethanechol, carbachol, pilocarpine, muscarine, ACh, methacholine
Muscarinic antagonists?
Atropine, hyoscine, ipratropium, pirenzepine, tiotropium
What is pilocarpine used for clinically?
Eye drops to cause miosis, glaucoma treatment; increased lacrimal secretion and salivation for dry mouth/dry eyes (Sjogren’s syndrome)
What is bethanechol used for clinically?
Rarely used but stimulant laxative, bladder emptying stimulation
What is an example of cardiovascular antimuscarinic?
Atropine - treatment of sinus bradycardia
Opthalmic antimuscarinics (2)?
To dilate pupils (mydriasis) - tropicamide, cyclopentolate
