Lecture 7 Flashcards
What are the catecholamines?
dopamine, noradrenaline, adrenaline
What is one example of a tryptamine?
Serotonin
What is the first step of noradrenline synthesis
Tyrosine hydroxylase converts L-tyrosine to dihydroxyphenylalanine (DOPA)
Where is tyrosine hydroxylase found?
- NA and DA neurones - adrenal chromaffin cells
What is the second step of noradrenline synthesis?
DOPA decarboxylase converts dihydroxyphenylalanine (DOPA) to dopamine
What is the final step of noradrenaline synthesis?
Dopamine-β-hydroxylase converts dopamine to noradrenaline
Where is dopamine-β-hydroxylase found?
NA vesicles
What is the role of phenylethanolamine N-methyl transferase?
- converts noradrenaline to adrenaline in adrenal chromaffin cells of adrenal medulla
What drug inhibits tyrosine hydroxylase and what does this inhibit?
- 𝛼-methylparatyrosine - inhibits DOPA production
What drug inhibits DOPA decarboxylase and what does this inhibit?
- carbidopa and benserazide - inhibits dopamine production
What drug inhibits dopamine-β-hydroxylase and what does this inhibit?
- disulfarim (antabuse) - inhibits noradrenaline production
Name examples of drugs inhibiting storage of noradrenaline
- Reserpine - 𝛼-methyl DOPA
How does reserpine work?
1) inhibits NA uptake 2) depletes monoamines 3) decrease in sympathetic function - damages vesicles - decreases HR and BP
What are side effects of reserpine?
- postural hypotension - hypothermia - sedation - depression (suicidal at high doses)
How does 𝛼-methyl DOPA work?
1) coverted to 𝛼-methyl NA 2) replaces/displaces NA 3) released instead of NA - less potent at 𝛼1 and activates 𝛼2= less NA release - decreases HR and BP
What does 𝛼-methyl DOPA treat?
Hypertension e.g. in pregancy
What is the role of 𝛼2 adrenoceptors in noradrenaline release?
Presynaptic inhibitory autoreceptors= inhibit Ca2+ release
Name a drug that inhibits noradrenaline release
Clonidine
How does clonidine work?
- 𝛼2 agonist - decreases NA release
What is clonidine used to clinically treat?
- hypertension - migraines - Tourette’s - menopausal flushing
What are the two uptake mechanisms of noradrenaline?
- norepinephrine transporter (NET) - extraneuronal monoamine transporter (EMT)
What are the enzymes involved in noradrenaline/monoamine metabolism?
- monoamine oxidase (MAO) - catechol-o-methyl transferase (COMT) - aldehyde dehydrogenase (ADH)
What are MAO inhibitors used for?
Depression
What are COMT inhibitors used for?
Parkinson’s disease
What are the subtypes of 𝛼 adrenoceptors?
𝛼1, 𝛼2
What are the subtypes of β adrenoceptors?
β1, β2, β3
Which is more effective at 𝛼 adrenoceptors- noradrenaline or isoprenaline?
Noradrenaline
Which is more effective at β adrenoceptors- noradrenaline or isoprenaline?
Isoprenaline
What is the physiological response of 𝛼1 activation?
Contraction
Where is the 𝛼1 receptor expressed?
Vascular and vas deferens smooth muscle
What is the physiological response of 𝛼2 activation?
Decreased noradrenaline release
Where is the 𝛼2 receptor expressed?
Adrenergic nerve terminals
What is the physiological response of β1 activation?
Increased heart rate and force of contraction
Where is the β1 receptor expressed?
Cardiac muscle
What is the physiological response of β2 activation?
Dilation and relaxtion
Where is the β2 receptor expressed?
- cardiac blood vessels - skeletal muscle blood vessels - bronchial smooth muscle
What is the physiological response of β3 receptor activation?
Lipolysis
Where is the β3 receptor expressed?
Adipose tissue
What G protein subtype does 𝛼1 receptors bind to?
G𝛼q
What is the physiological response of G𝛼q activation?
Contraction of vascular smooth muscle
What are the second messengers of G𝛼q?
- protein kinase C (PKC) - Ca2+
What G protein subtype does 𝛼2 receptors bind to?
G𝛼i
What is the physiological response of G𝛼i activation?
Decreased insulin and noradrenaline release
What are the second messengers of G𝛼i?
- (Reduced activity of) cAMP and PKA - Gβ𝛾 inhibits voltage gated Ca2+ channels
What G protein subtype does β1, 2 and 3 receptors bind to?
G𝛼s
What is the physiological response of G𝛼s activation?
- increased cardiac output - dilation/relaxation - lipolysis
What are the second messengers of G𝛼s?
(Increased activity of) cAMP and PKA
What are the mechanisms of G𝛼q activation?
1) stimulates phospholipase C β (PLCβ) 2) breaks down PIP2 to diacylglycerol (DAG) and IP3 - DAG activates PKC - IP3 causes influx of Ca2+
What are the mechanisms of G𝛼i activation?
1) inhibits adenylate cyclase (AC) 2) reduction in cAMP, PKA activation and Ca2+ activity 3) Gβ𝛾 activates K+ channels leading to an efflux from the cell- hyperpolarisation and reduced excitability
What are the mechanisms of G𝛼s activation?
1) stimulates adenylate cyclase 2) increased cAMP and activation of PKA
List examples of directly-acting noradrenergic agonists
- noradrenaline - adrenaline - salbutamol
What is the physiological response of noradrenaline
Increased BP due to 𝛼1 vasoconstriction
What is noradrenaline used to treat clinically?
- shock - cardiac arrest
What is the physiological response of adrenaline?
- increased heart rate - increased force of contraction - bronchodilation
What are the clinical uses of adrenaline?
- treat cardiac arrest - treat anaphylactic shock - local anaesthetics
What is the physiological response of salbutamol?
Smooth muscle relaxation e.g. bronchodilation
What is salbutamol used to treat clincially?
- asthma - inhibition of premature labour
Name an example of an indirectly-acting noradrenergic agonist
Tyramine
How does tyramine work?
- stimulates NA release - competes with NA for NET - displaces NA from vesicle
What is the cheese reaction?
- Tyramine (cheese) - normally metabolised by MAO - With MAOIs amine levels increase - act as indirect sympathomimetics - provoke hypertensive crisis
List examples of alpha adrenoceptor antagonists
- prazosin - lebatolol
What is the physiological respojnse of prazosin and labetolol?
Decreased blood pressure due to 𝛼1 block
How does prazosin work?
- treats hypertension - few side effects - no reflex increase HR
How does labetolol block a reflex heart rate increase?
Blocks β1 receptors
List examples of β adrenoceptor antagonists
- propranolol - atenolol
List an example of a β adrenoceptor partial agonist
Pindolol
Is propranolol β selective or non-selective?
Non-selective
Is atenolol β selective or non-selective?
β1 cardioselective
What is the physiological response of propranolol?
- decreased HR, BP and cardiac output
What are the side effects of propranolol?
- bronchoconstriction (β2) - sleep disturbance - hypoglycaemia - cardiac failure - cold extremities
What is propranolol used for?
- angina - dysrhythmias
What is the physiological response of atenolol?
Decreased HR, BP and cardiac output via β1 block
What is atenolol used for?
Hypertension
What is the physiological response of pindolol?
- partial agonists - don’t give max response - inhibit action of full agonists
What is pindolol used for?
hypertension