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FNP > GPCR > Flashcards

GPCR Flashcards

1
Q

What is the sympathetic nervous system?

A

Sympathetic nerves release noradrenaline.
Adrenal medullae release adrenaline and noradrenaline - catecholamines

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2
Q

What are the types of receptor which catecholamines binds?

A

a-adrenoceptors
b-adrenoceptors

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3
Q

What is the agonist potency order of a1 adrenoceptors?

A

Noradrenaline >adrenaline&raquo_space; isoprenaline

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4
Q

What is the agonist potency order of a2 adrenoceptors?

A

Adrenaline > noradrenaline&raquo_space; isoprenaline

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5
Q

What is the agonist potency order of b1 adrenoceptors?

A

Isoprenaline > noradrenaline > adrenaline

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6
Q

What is the agonist potency order of b2 adrenoceptors?

A

Isoprenaline > adrenaline > noradrenaline

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7
Q

What is the agonist potency order of b3 adrenoceptors?

A

Isoprenaline > noreadrenaline = adrenaline

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8
Q

What are adrenergic receptors?

A

Part of the family of G protein coupled receptors.
Recruit G proteins to produce cellular effects
Integral membrane protein

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9
Q

What is the structure of adrenergic receptors?

A

Single polypeptide chain.
Extracellular N-terminus, intracellular C-terminus (carboxylic acid end)
7 transmembrane a helices
Binding site buried within a cleft between the a helices

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10
Q

What is the specificity of G-protein coupled receptors?

A

a, and b-adrenoceptors recruit different intracellular G proteins.
So, a and B adrenoceptors utilise different intracellular messaging systems to produce their cellular effects.
The long third cytoplasmic loop is the region of the receptor that couples to the G protein.

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11
Q

What are G-protein coupled receptors?

A

Have 3 subunits - alpha, beta and gamma
When bound to receptor, it is in GDP form.
When an agonist binds, it causes the G protein to be phosphorylated and GDP forms GTP.
This makes the G protein unstable, so a-subunit dissociates from beta-gamma subunit and moves in membrane to act on target protein, to mediate effects in the cell.

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12
Q

What is the mechanism of a1 adrenoceptors on G-proteins?

A

a1 adrenoceptors are coupled to Gq proteins.
Noradrenaline binds to receptor, which phosphorylates Gq protein.
The a-subunit dissociates and activates phospholipase C, which acts on the phospholipid PIP2.

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13
Q

What are the effects of the a1 adrenoceptor?

A

PIP2 produces inositol triphosphate (IP3) and diacylglycerol (DAG).
IP3 releases Ca2+ from the endoplasmic reticulum, which will have an effect depending on the cell type - smooth muscle contracts, secretory organ secretes.
DAG activates protein kinase C, which phosphorylates proteins.

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14
Q

What is the mechanism of a2 adrenoceptors?

A

Noradrenaline binds to a2-adrenoceptors, which is coupled to Gi protein.
a-subunit binds to adenylyl cyclase, and inhibits it.

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15
Q

What is the effect of a2-adrenoreceptors?

A

Adenylyl cyclase is inhibited so it cannot convert ATP to cyclic AMP, so cAMP levels are decreased.
cAMP can not activate protein kinase A, so there is reduced activity of PKA.
Therefore there is reduced phosphorylation of proteins.

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16
Q

What is Yohimbine?

A

Blocks the a2 adrenoceptor antagonist, which inhibits the inhibitory affect of the a-subunit, so amplifies sympathetic function.

17
Q

What is the mechanism of B-adrenoceptors?

A

Noradrenaline binds to B-adrenoceptor, which is coupled to Gs protein.
The a-subunit binds and stimulates adenylyl cyclase.
This converts ATP to cAMP, which activates protein kinase A, so there is increased phosphorylation of intracellular proteins.

18
Q

What is the relationship between a2 and B adrenoceptors?

A

They have an opposing effect.
a2 adrenoceptor effect on smooth muscle will cause contraction.
b adrenoceptor effect will cause relaxation.

19
Q

What are the B1 adrenoceptors that act on the heart?

A

Sino-atrial node - increased heart rate.
Atrio-ventricular node - increased conduction velocity.
Atria - increaed contractility
Ventricles - increased contractiliity, enhanced automaticity.

20
Q

How does the sino-atrial node increase heart rate?

A

Sympathetic nerves release noradrenaline whcih acts on the b1 adrenoceptors.
These activate the Gs pathway, and increases heart rate.

21
Q

What are adrenoceptors in the smooth muscle?

A

Blood vessels - a1 causes constriction, b2 causes dilation
Bronchi - b2 dilation
GI tract - a1 and a2 contraction of sphincters, b2 relaxation.
Uterus - b2 relax
Adipose tissue - b3 lipolysis, thermogenesis.

22
Q

What agonists act on adrenoceptors?

A

Phenylephrine on a1 adrenoceptors for cold remedies
Clonidine acts on a2 in brain
Dobutamine increases force of contraction on heart by b1 adrenoceptors.
Salbutamol for asthma on b2.
Mirabegron on b3.

23
Q

What is isoprenaline?

A

A non-selective b-adrenoceptor agonist.

24
Q

Where are the b adrenoceptors?

A

B1 receptors are in the heart, so drugs acting on b1 will affect the heart.
B2 are in the lungs.
B3 in bladder and fat.

25
Q

Where are a-adrenoceptors found?

A

a1 are found in the blood vessels.
a2 are found in the brain and in the periphery.

26
Q

What antagonists act on adrenoceptors?

A

a1 - prazosin and doxazosin.
a2 - yohimbine and idazoxan
b1 - atenolol, slows down heart rate.
b2 - butoxamine.

27
Q

What is doxazosin?

A

A hypotensive drug.
It inhibits the a1-adrenoceptors on blood vessles, which stops activation of the a1-Gq pathway, and causes relaxation of the heart.

28
Q

What is propranolol?

A

A non-selective B-adrenoceptor antagonist.

29
Q

What is Adrenaline?

A

Mixed a and b receptor agonist.
Uses:
Cardiac arrest
Acute anaphylaxis
Severe asthma
Prolongation of local anaesthetic action.

30
Q

What are characteristics of adrenaline?

A

Poorly absorbed by GIT, so given intramuscularly or subcutaneously.
Rapidly removed by tissues.
Metabolised by MAO and COMT.

31
Q

What is dobutamine?

A

Selective B1 receptor agonist
Cardiogenic shock.
Given intravenously
Plasma half-life 2 minutes
But can cause arrythmia

32
Q

What is salbutamol?

A

Selective b2 receptor agonist - lungs.
Opens up airways - used for asthma, delay of premature labour.
Gs pathway, acts on adenylyl cyclase, increases cAMP levels, causes relaxation.

33
Q

What is mirabegron?

A

Prodrug for a selective B3 receptor agonist.
Used for treatment of overactive bladder syndrome.

34
Q

What is phenylephrine?

A

Selective a1-adrenoceptor agonist.
For nasal decongestion.
Metabolised by MAO.

35
Q

What are a2 receptor agonists?

A

Clonidine - hypertension, migraine.
Dexmedetomidine - IV sedation without respiratory depression.

36
Q

What are the uses of a-adrenoceptor antagonists?

A

Hypertension - a1-antagonists. Prazosin short acting, doxazosin long acting, reduces blood pressure.
Benign prostatic hypertrophy - a1 receptor antagonist - tamsolusin.
Phaeochromocytoma - tumour of adrenal gland, non-selective a antagonist, by phenoxybenzamine.

37
Q

What are the uses of B-adrenoceptor antagonists?

A

Cardiovascular - hypertension, ischaemia, angina.
Glaucoma - drainage of aqueous humour by timolol.
Thyrotoxicosis
Anxiety - palipitations by propranolol

38
Q

What are the adverse effects of B-adrenoceptor antagonists?

A

Bronchoconstriction - avoid using in asthmatic patients
Worsens pre-existing cardiac failure as slows heart rate
Bradycardia
Hypoglycaemia
Physical fatigue
Cold extremities

FNP (12 decks)

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