muscarinic pharmacology Flashcards

1
Q

what concentrations of Ach are required for muscarinic action

A

low concentrations of Ach are required for muscarinic activation, nicotinic actions requier high Ach concentrations

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2
Q

what is dale’s experiment?

A

dale measured blood pressure in response to different concentrations of Ach and presence of hexamothonium and atropine

small dose of Ach causes muscarinic actions; vasodilation

this is repeated in presence of atropine, no change in blood pressure seen

larger dose of Ach in presence of atropine stimulates ganglia, causes increase in blood pressure.

a secondary peak is also seen due to delayed action on adrenal medulla; causing vasoconstriction and tachycardia

hexamethonium is then added, reducing blood pressure to normal by inhibiting Ach nicotinic action

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3
Q

how are muscarinic receptors activated endogenously and what is their effect?

A

muscarinic receptors are innervated except in most blood vessels excluding genitals

stimulation of muscarinic receptors causes smooth muscle in eye, bronchi, GIT, and bladder to contract

in blood vessels including genitals muscarinic receptors cause smooth muscle relaxation/ vasodilation

in glands they cause secretion

in heart they slow rate via the vagus nerve which innervates SAN and AVN and conduction, but no effect on force of contraction

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4
Q

what are agonists of acetylcholine receptors and which ones do they work on, and what is rate of hydrolysis by cholinesterase

A

Ach: agonist for both N and M, quickly hydrolysed by cholinesterase

methacholine: agonist only for M, slowly hydrolysed by cholinesterase
carbachol: agonist for both N and M, resistant to cholinesterase

bethanechol, pilocarpine and muscarine: all only M agonists, and resistant to cholinesterase

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5
Q

what is the effect of atropine? and how is it used therapeutically

A

atropine is muscarinic antagonist

may increase heart rate, cause pupil dilation and paralysis of eye accommodation

is an antiemetic (used to treat motion sickness), used to treat parkinsons to reduce tremor,

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6
Q

what happens when muscarinic receptors in eye are activated

A

pupil constriction, ciliary muscles contract causes lens to relax into fat shape which accomodates for near vision

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7
Q

what are muscarinic agonists used for therapeutically?

A

treatment of glaucoma, since ciliary eye spasm helps drain aqueous humour

treatment of dry mouth

to relieve paralytic ileus after surgery

to relieve urinary retention

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8
Q

what are muscarinic antagonists used for therapeutically and what are main 3 drugs used

A

anaesthesia

to reduce the effects of cholinesterase inhibitors, such as in anticholinesterase poisoning

used to induce mydriasis and ciliary muscle paralysis

relief of smooth muscle spasm such as in COPD

treatment of parkinsons, motion sickness, urinary incontinence

main 3 drugs used: atropine, hyoscine and homatropine, all competitive antagonists

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9
Q

what other drugs can block muscarinic receptors

A

antipsychotics, antidepressants and antihistamines may sometime block muscarinic receptors

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10
Q

how do parasympthamimetic drugs act on muscarinic receptors

A

stimulate them, either via direct stimulation of by inhibiting ChE

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11
Q

what main agonist drugs of MAchRs are used clinically and why?

A

methacholine and carbachol since they have a longer duration of action than Ach since no cholinesterase hydrolysis

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12
Q

how are muscarinic agonist drugs administered

A

methacholine and carbachol are fully ionised, so not given orally

pilocarpine only partially ionised at physiological pH so is absorbed topically

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13
Q

what are physiological effects of muscarinic antagonist drugs in periphery

A

resembles activation of sympathetic system:

block of secretions

tachycardia: due to block of vagal inhibition of heart, no change in blood pressure since most blood vessels do not have parasympathetic innervation

pupillary dilation (mydriasis), cycloplegia (cilliary muscle paralysis)

inhibition of motility and secretions of GIT

other smooth muscle relaxed

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14
Q

what are physiological effects of muscarinic antagonists on CNS

A

atropine has no great effect in small doses, but at high doses causes stimulation, restlessness, hallucinations and disorientation

hyoscine is powerful CNS depressant, causing sleep and amnesia, also an anti-emetic

atropine like drugs supress tremor in parkinsons

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15
Q

how are muscarinic receptors characterised

A

they are blocked by atropine

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