Pharm 504: Neuroeffector Junction Iii

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PHARM 504: NEUROEFFECTOR JUNCTION III

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PHARM 504: NEUROEFFECTOR JUNCTION III

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What is cholinomimetic?

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Drugs that mimic the effects of parasympathetic nerve stimulation by activation or potentation of cholinergic receptor responses.

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Two classes of direct acting agonists?

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1. choline esters
2. natural plant compounds

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What are some examples of choline esters?

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1. ACh
2. methacholine
3. carbachol
4. bethanecol

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Describe char of bethanecol

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1. Not an esterase
2. has muscarinic receptor
3. no nicotinic receptor

Not hydrolyzed by cholinesterase. Very weak agonist and it's primarily a muscarinic agonist.

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Examples of natural plant compounds as direct acting agonists?

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1. pilocarpine
2. muscarine

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Pilocarpine

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1. alkaloid primarily with muscarinic actions
2. lipophilic

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Muscarine

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Muscarinic agonist

From mushrooms

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Atony

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Muscles that lost their strength and tone.

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Bethanecol's therapeutic role in intestinal atony?

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Increase peristalsis and micturition (urination) by activation of muscarinic receptors.

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Pilocarpine's therapeutic role in glaucoma? Mechanism of action?

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Lowers pressure

Glaucoma: buildup of pressure due to problem with secretion of aqueous humor or its drainage--> inc intraoccular pressure.

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Muscarinic receptor activation's effect on the eye?

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Widens angle of eye by contraction of iris and ciliary muscles--> promotes drainage of aqueous humor through canal of schlemm.

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Example of indirect acting agonist?

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Reversible inhibitors of ACh-esterase--> indirectly increases conc of ACh and prolongs lifetime.

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Organophosphates

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1. insecticides
2. ecothiophate
3. military nerve gases

Very lipophilic

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Physiostigmine

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1. An indirect acting agonist
2. competes with muscarinic blockers and overcomes blockade.
3. increases ACh

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Myasthenia gravis

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Autoimmune disease with antibodies to nicotinic receptors

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Edrophonium

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Reduces muscle weakness by increasing amount of ACh.

Used as diagnostic of myasthenia gravis.

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Muscarinic receptor antagonist

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Competitive antagonists of muscarinic receptors.

Act at agonist binding site to induce surmountable block.

An agent that reduces the activity of the muscarinic acetylcholine receptor.

Basically functions mediated by muscarinic receptors are blocked!

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Examples of muscarinic receptor antagonist

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Atropine

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Atropine

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Causes tachycardia but no change in MAP.

Opposes the actions of the vagus nerve, blocks acetylcholine receptor sites, and decreases bronchial secretions.
In general, atropine lowers the parasympathetic activity of all muscles and glands regulated by the parasympathetic nervous system. This occurs because atropine is a competitive antagonist of the muscarinic acetylcholine receptors (acetylcholine being the main neurotransmitter used by the parasympathetic nervous system).

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High doses of atropine can cause/

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1. hallucinations
2. disorientation
3. respiratory depression

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Functions of atropine?

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1. decreases
2. pupil dilatation (mydriasis)

Atropine induces mydriasis by blocking contraction of the circular pupillary sphincter muscle, which is normally stimulated by acetylcholine release.