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Autonomic Pharamcology 2 2016
Acetylcholine receptors and their drugs
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Occur in ANS ganglia and parasympathetic targets
Neuromuscular blocking drugs
Two categories: non-depolarising and depolarising blocking drugs
These use different mechanisms to achieve the same aim

Non-depolarising blockers
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Tubocurarine extracted from curare (mixture of plant alkaloids)
Synthetic drugs: gallamine, pancuronium and atracurium
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Blocking receptors causes a decrease in end-plate potential

Effect of tubocurarine
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There is still a response in the presence of tubocurarine because a few neurons can still
release AP’s
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Low-blood pressure is a side-effect (less so with synthetic drugs) when it acts on ganglia
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Depolarising blocking drugs:
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Decamethonium – more complex actions than non-depolarising blockers
Inject chicks 0 initial muscle spasms, then flaccid paralysis
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Uses of non-depolarising blockers:
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Anaesthesia (suxamethonium is shorter acting, more useful)
Depolarising blockers ineffective in Myasthenia Gravis ( autoimmune disease where
antibodies cause fewer nicotinic receptors at the end-plate)
o These patients are hypersensitive to non-depolarising blockers since they need less
antagonist to block fewer receptors

Can we overcome depolarising and non-depolarising blockers
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Drugs that clock AChE overcome non-depolarising but not depolarising blockers
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Ganglion-activating drugs
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Decamethonium and suzamethonium stimulate NMJ (Nm receptors)
Nn receptors stimulated by nicotine and lobeline which cause depolarisation at autonomic
ganglia
Almost no clinical uses since they stimulate most ANS nerves
Inhibit post-synaptic actions of Ach at Nn receptors (non-depolarising)
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Increase carbon length and you change the effects
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However, heart rate and postural reflexes are blocked
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Slow Heart rate, exocrine secretion (salivation etc)
All bind M receptor subtypes

Uses of muscarinic antagonists
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Premedication in anaesthesia (inhibit bronchial and salivary secretions, and reflex
bronchoconstriction
GI disorders (reduce gastric secretions in peptic ulcers) Pirenzipine is the most selective for
this
Ophthalmology exams (pupil dilation)
Reduce motion sickness (hyoscine effective as it can get across blood-brain barrier to have
CNS actions



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