DGN - Adrenoceptor Subtypes Flashcards
What is the evidence for adrenoceptor subtypes at the noradrenergic synapse?
Neurochemical experiments by S Langer
What is an important concept related to feedback inhibition at the synapse?
There is feedback inhibition of neurotransmitter release at the synapse mediated by AUTORECEPTORS (a2)
What are the 2 types of α adrenoceptors?
α1 - predominantly postsynaptic
α2- predominantly presynaptic
Which drug will have antihypertensive action?
Agonists:
- Phenylephrine α1> α2
- Methoxamine α1
- Clonidine α2
Clonidine α2
- Inhibits noradrenaline release
Which drug(s) will be antihypertensive?
Antagonists:
- Phentolamine α1 = α2
- Phenoxybenzamine α1
- Prasozin α1 > α2
- Yohimbine α2 > α1
Phenoxybenzamine α1
- blocks noradrenaline binding to postsynaptic membrane
Name the β adrenoceptors and their associated effects (8)
β1
- Cardiac acceleration
- Lipolysis
- Decreased gut motility & secretion
- Renin release
β2
- Bronchodilation
- Vasodilation of blood vessels to skeletal muscle
- Glycogen breakdown
Which drug is used for the treatment of asthma and is associated with a high incidence of heart failure ?
Isoprenaline
β1 > β2
Which drug is an effective bronchodilator by inhalation ?
Salbutamol
β2 > β1
More effective treatment of asthma as does not result in a high incidence of heart failure
Which drug is used as a cardiac stimulant ?
Dobutamine
β1 > β2
Name some β Adrenoceptor antagonists (2)
PROPRANOLOL
- Non-selective beta blocker
- Antihypertensive
Has local anaesthetic action; can cause bronchoconstriction
ATENOLOL
- β1 antagonist
- Cardioselective
How is acetylcholine synthesised?
Substrates are:
- Choline
- AcetylCoA
Choline is taken up into the nerve terminal by the choline transporter
- This is the rate-limiting step for the synthesis
The enzyme is choline acetyltransferase (CAT)
AcetylCoA + choline Acetylcholine + CoA
What process takes up acetylcholine into presynaptic vesicles?
An active transport process
- Blocked by vesamicol
What breaks down ACh in the synaptic cleft?
Acetylcholinestrase
ACh —> choline and acetic acid
How is choline taken back up into the nerve terminal?
By the choline transporter
- Blocked by hemicholinium
What effects does ACh have on muscarinic receptors Cardiovascular, Gastrointestinal and Exocrine gland secretion?
CARDIOVASCULAR
- Decreased HR, CO
- Vasodilation
GASTROINTESTINAL ACTIONS
- Increased activity
EXOCRINE GLAND SECRETION
- Increased sweating
- Lacrimation
- Salivation
