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LIFE207 > SAR At Adrenoreceptors > Flashcards

SAR At Adrenoreceptors Flashcards

1
Q

What is the synapse bridging a neuron and a muscle?

A

A neuromuscular junction

Broad term is ‘neuroeffector junction’

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2
Q

What’s the benefit of ACh being synthesised in the neuron?

A

Rapid response

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3
Q

What combines to form ACh?

A

Acetyl CoA and choline

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4
Q

What enzyme catalyses the formation of ACh?

A

Choline acetyl transferase

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5
Q

What’s the benefit of ACh being packaged in vesicles?

A

Protects ACh from degradation

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6
Q

What’s the mechanism of releasing ACh?

A

ACh is stored into vesicles

Action potential releases ACh

ACh acts on nicotinic receptors - opening ion channel and causing a response

2 ACh molecules are required at nicotinic receptors for a response

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7
Q

How is ACh action terminated? What happens?

A

Acetylcholine esterase enzyme breaks ACh down into acetic acid and choline, ceasing a response

This is done rapidly, 10,000s of ACh broken down per second

Choline is reclaimed by nerve ending through a choline carrier protein - rate limiting step in ACh synthesis

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8
Q

What drugs interfere with processing of ACh? How do they work?

A

Vesamicol - blocks transfer of ACh into vesicles

Botulinum toxin - blocks release of ACh from nerve endings

Anticholinesterases - prevents hydrolysis of ACh by AChE in synapse

Hemicholinium - blocks reuptake of choline by NMJ

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9
Q

What is the synthesis of noradrenaline?

A

Tyrosine is SM

Tyrosine converted to DOPA by tyrosine hydroxylase

DOPA converted to Dopamine by Dopa decarboxylase

Dopamine converted to noradrenaline by Dopamine ß hydroxylase

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10
Q

Where does noradrenaline synthesis occur and what is RDS?

A

Occurs in noradrenergic nerves

Tyrosine hydroxylase is RDS

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11
Q

How is NA stored?

A

NA is co-packaged with ATP into vesicles - co-transmission

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12
Q

What is the process of NA release?

A

Ca2+ enters nerve ending which activates exocytosis of NA from storage vesicles

NA is released and acts on alpha or ß receptor on post-synaptic membrane

It also acts on alpha2 on pre-synaptic nerve which inhibits cAMP production, which inhibits Ca2+ ion channel uptake into nerve ending

It is a negative feedback loop, inhibition of transmitter release.

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13
Q

What is the negative feedback loop of NA release described as?

A

Autoinhibitory feedback mechanism

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14
Q

What drugs affect the release mechanism of NA?

A

Disulfuram - inhibits dopamine hydroxylase, hence inhibiting NA synthesis. Mainly used for its action of alcohol, causing worse hangovers

Reserpine - blocks mechanism that transports NA into vesicles

Tyramine/amphetamine - increase release of NA from vesicles

Nimodipine - reduces release by blockade of Ca2+ channels in nerve terminals

Any alpha2 adrenoreceptor-agonist

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15
Q

What are the different subtypes of the adrenoreceptors?

A

Alpha1 and alpha2

ß1, ß2, ß3

Different subtypes can mediate similar or different responses

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16
Q

Where are alpha1 adrenoreceptors found?

A

Blood vessels
Gut smooth muscle
Uterus
Liver

17
Q

Where are alpha2 adrenoreceptors found?

A

Blood vessels

Gut smooth muscle

18
Q

Where are ß1 adrenoreceptors found?

A

Heart - betablockers

19
Q

Where are ß2 adrenoreceptors found?

A

Blood vessels
Lungs
Gut smooth muscle
Uterus
Kidney
Liver

20
Q

What’re the main effects of alpha1 adrenoreceptors?

A

Contraction of smooth muscle - relaxation in gut

Salivary secretion

Hepatic glycogenysis

21
Q

What’re the main effects of alpha2 adrenoreceptors?

A

Inhibition of transmitter release

Platelet aggregation

Contraction of vascular smooth muscle

Decreases insulin release

22
Q

What’re the main effects of ß1 adrenoreceptors?

A

Cardiac rate and force

23
Q

What’re the main effects of ß2 adrenoreceptors?

A

Bronchodilation
Vasodilation
Relaxation of gut smooth muscle
Hepatic glycogenolyis
Muscle tremor

24
Q

What’re the main effects of ß3 adrenoreceptors?

A

Lipolysis - lipid breakdown

25
Q

What receptor subtypes does adrenaline act at?

A

Alpha1, alpha2, ß1, ß2

26
Q

What receptors does NA act?

A

Alpha1, alpha2, ß1 and B2

27
Q

What receptors does isoprenaline act?

A

ß1 and ß2

28
Q

Name an alpha1 and alpha2 agonist.

A

Alpha1 = phenylephrine

Alpha2 = clonidine - high blood pressure, not used clinically so much anymore

29
Q

Name a ß1 and ß2 agonist.

A

ß1 = dobutamine - heart failure
ß2 = salbutamol, terbutaline - asthma

30
Q

What’re 2 non-selective alpha antagonists?

A

Phentolamine and phenoxybenzamine

31
Q

Name an alpha1 and alpha2 antagonist.

A

Alpha1 = prazosin - antihypertensive

Alpha2 = yohimbine

32
Q

Name a non-selective ß1 and B2 agonist

A

Propranolol - cardiovascular, glaucoma, thyrotoxicosis, tremor, migraine prophylaxis and anxiety

33
Q

Name a ß1 and ß2 antagonist

A

ß1 = atenolol - cardiovascular, antihypertensive

ß2 = butoxamine

34
Q

By what processes is NA removed from the synapse?

A

Uptake 1 - neuronal re-uptake in presynaptic membrane, relatively selective for NA (tyramine)

Uptake 2 - extraneuronal re-uptake in post-synaptic tissue, takes up noradrenaline, adrenaline ans isoprenaline

35
Q

What enzymes metabolise endo/exogenous catecholamines?

A

Monoamine oxidase (MAO) - pre-synaptic nerve

Catechol-O-methyl transferase (CMOT) - post synaptic tissue

36
Q

What is the relative abundance distribution of MAO and COMT?

A

MAO is abundant in sympathetic nerve endings

COMT is widely distributed in effector cells and also present in extracellular space
- more important for metabolism of circulating adrenaline and some drugs, i.e. isoprenaline

37
Q

What’s the relative efficientcy of MAO and COMT compared to AChE?

A

AChE&raquo_space; MAO/COMT

38
Q

What drugs affect the uptake of NA? What pathway?

A

Cocaine/desipramine blocks uptake 1

Phenoxybezamine and other steroid hormones block uptake 2 - extraneuronal re-uptake

MAO is inhibited by Tranylcypromine and Iproniazid

MAOIs used in treatment of depression

LIFE207 (9 decks)

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