Adrenergic effects Flashcards
What are the nerve fibres like in the sympathetic nervous system
There are short pre-ganglionic nerve fibres and long post-ganglionic nerve fibres
What receptors do sympathetic nerves have
nicotinic acetylcholine receptors
What is the main neurotransmitter in the sympathetic nervous system and where does it act
Noradrenaline
It acts on the adrenergic G coupled receptors
How is DOPA (dihydroxyphenylalanine) made
Tyrosine is converted to DOPA by the action of tyrosine hydroxylase
This is the rate determining step
How is dopamine made
DOPA is converted to dopamine by the action of DOPA decarboxylase
What is dopamine used for
Its a neurotransmitter in the brain
Its involved in many pathways especially reward-motivated behaviour
How is noradrenaline made
Dopamine is converted to noradrenaline by the action of dopamine beta-hydroxylase
Where and how is adrenaline made
In the adrenal medulla, noradrenaline is converted to adrenaline by the action of phenylethanolamine N-methyltransferase (PNMT)
What is sympathomimetics
A drug that mimics or looks like you’ve stimulated the sympathetic nerves
What is indirect sympathomimetics
These drugs overstimulate the sympathetic nervous system
What is direct sympathomimetics
When the drug is an agonist which will bind to the receptor taking the place
What is isoprenaline
A synthetic stimulator
What is the order in sensitivity of stimulators on alpha receptors
- Noradrenaline
- Adrenaline
- Isoprenaline
What is the order in sensitivity of stimulators on beta receptors
- Isoprenaline
- Adrenaline
- Noradrenaline
What type of receptor is an alpha 1 receptor
Gq protein coupled receptor
What happens when alpha 1 receptors are activated
Phospholipase C is activated
Splits PIP2 into IP3 and DAG
IP3 causes calcium release from smooth ER
DAG causes kinase C production
What are the physical outcomes of alpha 1 receptor stimulation
Vascular smooth contraction; vasoconstriction in blood vessels
Contraction of seminal vesicles; iris muscle (pupil dilation) and pilomotor muscle
What are alpha 1 agonists
Phenylephrine and oxymetazoline
What are alpha 1 antagonists
Prazosin, doxazosin and tamsulosin
What type of receptor is an alpha 2 receptor
Gi protein coupled receptor
What happens when alpha 2 receptors are activated
Inhibits adenylate cyclase
therefore decreases cAMP production so protein kinase A production reduced
What are the physical outcomes of alpha 2 receptor stimulation
Inhibition of transmitter release from sympathetic nerves
The likely hood of the calcium channels on the adrenergic neurone opening is less even if depolarisation occurs since there is a lack of protein kinase A
What are alpha 2 agonists
Clonidine
What are alpha 2 antagonists
Yohimbine
What type of receptor is a beta 1 receptor
Gs protein coupled receptor
What happens when beta 1 receptors are stimulated
Activates adenylate cyclase therefore increases cAMP production so protein kinase A production is increased
What are the physical outcomes of beta 1 receptor stimulation
Positive chronotropy - Heart rate increases
Positive inotropy - Force increases
Positive lusitropy - Rate of relaxation increases
Positive dromotropy - Conduction velocity of atrioventricular node increases
What does cAMP do after beta 1 stimulation
Will interact with a pacemaker channel in the SAN that open up by hyperpolarisation
What does protein kinase A do after beta 1 stimulation
Makes calcium channels have a higher sensitivity to voltage therefore there is a larger influx of calcium ions
Stimulates potassium channels so the action potential depolarises quicker therefore there is a shorter action potential
Will affect calcium release channels, increases the uptake of calcium back into the sarcoplasmic reticulum - contraction is bigger but briefer
Where is the juxta glomerular apparatus (JGA) located
Between afferent and efferent renal arteries
What does the JGA do
- Increases renin release
- Renin converts inactive angiotensinogen to active angiotensin I
- This is turned into angiotensin II
What are the effects of angiotensin II
- Contracts vascular smooth muscle itself
- Increases the release of noradrenaline from sympathetic nerves
- Stimulates aldosterone which reabsorbs more water so you have an increase in circulating volume
What type of receptor is a beta 2 receptor
Gs protein coupled receptor
What happens when beta 2 receptors are stimulated
- Increased cAMP production
2. Increased K+ channel activity and decreased Ca release
What are the physical outcomes of beta 2 receptor stimulation
- Vascular dilation/airway relaxation
2. Decreased myosin light chain kinase and decreased contraction
What are beta 2 agonists
Salbutamol, salmeterol and clenbuterol
What are beta 2 antagonists
Propanolol
What type of receptor is a beta 3 receptor
Gs protein coupled receptor
What are beta 3 agonists
Mirabegron
What are the physical outcomes of beta 3 receptor stimulation
Enhancement of lipolysis in adipose tissue
Whats the treatment of an overreactive bladder
The beta 3 agonist mirabegron
What is a nasal decongestant
The alpha 1 agonist phenylephrine and ephedrine
Use of adrenoreceptor blockers
- Heart
- Kidneys
- Eye drops
- Atenolol
- Atenolol, less renin production
- Timolol
