Autonomic pharmacology Flashcards
What are the responses to acute stress? (Sympathetic drive).
- Increased heart rate and contractility
- Bronchodilation, increased respiratory rate and depth
- Vasoconstriction of skin but vasodilation of muscle
- Mobilisation of energy sources
- Dilation of pupils, better distant vision and night vision
- Reduction in secretion production
- Increase in muscle tone
- Reduction in pain
Inhibition of digestion, urination, erection
What are the responses of the parasympathetic nervous system?
Essentially directly opposes the effect of the sympathetic N.S.
- Decreased heart rate
- Decrease in respiratory rate
- Increased blood supply to the gut
- Building energy stores
- Constriction of pupils, better close up vision
- Increase in secretion production
- Increase in GI motility
- Defecation, urination, sexual arousal
Location of parasympathetic nerves.
Cranio-caudal
Location of sympathetic nerves.
Thoraco-lumbar.
Why does a high thoracic or cervical injury cause loss of sympathetic drive?
- The sympathetic nerves in the spine are damaged.
- The vagus nerve is not damaged.
- Unopposed parasympathetic innervation causes a bradycardia.
- Loss of sympathetic tone causes vasodilation and hypotension.
How is hypotension managed in a hospital setting?
Administration of vasopressors (epinephrine, norepinephrine).
How is bradycardia managed in a hospital setting?
Administration of anticholinergics (atropine).
What is a red flag in back injuries?
Loss of pain sensation from the injuries can mask hidden (internal) bleeding.
How do synapses work?
- AP arrives at axon terminal
- VGCC open
- Ca2+ enters the presynaptic neuron
- Ca2+ signals to NT vesicles
- Vesicles move to the membrane and dock
- NT release via exocytosis
- NT binds to receptor
- Signal is initiated in postsynaptic cell.
What are the different types of receptors of the sympathetic nervous system?
Alpha1 (postsynaptic) - vasoconstriction.
Alpha2 (presynaptic) - negative FB suppresses noradrenalin realease.
Beta1 - Increased HR and contractility.
Beta2 - Bronchodilation.
Treatment of meningitis with septic shock and MOF.
IV metaraminol - acts through peripheral vasoconstriction by acting as a pure alpha-1 adrenergic receptor agonist thus increases BP.
Blood pressure is determined by (3)
HR
SV
SVR - can be increased by using vasopressors such as metaraminol.
Chronic hypertension - why is prevention important?
Alpha blockers are useful treatment for hypertension -> causes vasodilation (Alfuzosin -suffix=zosin).
Step up treatment for hypertension post MI and prevention.
ACEi
Antiplatelets (aspirin, clopidogrel)
Statins (simvastatin)
Beta blocker (-olol)
Severe asthma attack
Oxygen
Salbutamol (Inhalers with spacer; nebulisers, IV)
IV Hydrocortizone
Oral Prednisolone
Alpha 2 agonists
Act presynaptically - reduce the amount of noradrenaline released.
Receptors found in the brain and spine.
They form a negative FB loop.
They work in a counter-intuitive manner:
- antihypertensives
- sedatives
- analgesics
Clonidine - sedative on ITU, orally for drug withdrawal, menopausal flushing and certain pain conditions.
Adrenaline
Stimulates ALL sympathetic receptors. (*This can cause problems).
Used in very serious situations.
Cardiac arrest - 1mg IV 1:10000
Anaphylaxis - 0.5mg IM 1:1000
Short duration of action and can be repeated every 3-5 mins.
Adrenaline and dilated pupils
Dilated pupils after a cardiac arrest aren’t always a sign of neurological injury.
Alpha 1 and Alpha 2 antagonists
Phenozybenzamine
Phentolamine
Alpha 1 antagonists
Prazosin
Doxazosin
Beta 1 and Beta 2 antagonists
Propanolol
Carvediol
Beta 1 antagonists
Metoprolol
Atenolol
Alpha 1, Alpha 2, Beta 1, Beta 2 agonists
Adrenaline (noradrenaline is a precursor)
Alpha 1, Alpha 2, Beta 1 Agonists
Noradrenaline (Dopamine)
Beta 1 and Beta 2 Agonists
Isoprenaline
Milrinone
Alpha 1 agonists
Phenylephrine, Metaraminol
Alpha 2 agonists
Clonidine, Dexmedetomidine
Beta 1 agonist
Dobutamine
Beta 2 agonist
Salbutamol
Too much beta 1 blockade can…
Effect beta 2 leading to bronchoconstriction - careful in asthma.
Too much beta 2 stimulation can
Affect beta 1 - tachycardia and tremor.
Which of the following are clinical uses for phenylephrine?
A - Decongestant nasal spray
B - Intra-penile injection for priaprism
C - During a C-section birth to manage hypotension
D - As a cream to treat haemorrhoids
E - All of the above
E - direct alpha 1 agonist, causes constriction of arteries and veins.
Which of the following drug - action pairings are correct?
A - Metaraminol - treats hypertension
B - Tamsulosin - treats Benign Prostatic Hyperplasia
C - Salbutamol - directly acts on beta 1 receptors
D - Carvedilol - safe for use in patients with asthma
E - Isoprenaline - reduces obesity
B
A - false, its an alpha 1 agonist so treats hypotension by causing vasoconstriction
B - True, its action as an alpha 1 blocker relaxes the smooth muscle of the bladder wall
C - False, salbutamol is a beta 2 receptor agonist (2 lungs!)
D - False, beta blockers, especially non-selective ones, can exacerbate asthma
E - False, Isoprenaline is a non-selective alpha and beta agonist. Beta 3 receptor is involved in lipolysis but B2AR agonist drugs for obesity are still in research stage
Vasovagal syncope
Emotional or environmental trigger (prolonged standing, fasting, dehydration, seeing blood or needles).
Activation of PNS.
Vasovagal reaction (bradycardia and vasodilation of peripheral blood vessels.
Drop in BP and reduction in Brain’s O2 supply.
Leads to cerebral hypoperfusion and loss of consciousness.
Farmer presenting with dyspnoea, lacrimation, salivation and eye pain.
Organophosphate poisoning.
They activate the PNS by inhibiting AChE so preventing the breakdown of ACh -> accumulates and overstimulates the nAChR and mAChr.
Atropine
Competes with ACh at the muscarinic receptors.
Nicotinic cholinergic receptor
Pre-ganglionic, SNS and PNS
Ligand gated ion channels
Action increases membrane permeability to Na+ and K+
Subgroups: ganglionic, neuromuscular and CNS
Muscarinic Cholinergic Receptors
GPCR
M1 - CNS, higher cognitive
M2 - Cardiac
M3 - Exocrine glands and smooth muscle
M4 - CNS only
M5 - CNS only
Nicotinic signs of AChEi toxicity
Mydriasis - dilation of pupil
Tachycardia
Weakness
Hypertension
Fasciculations - invol, rapid muscle twitches.
Muscarinic signs of AChEi (organophosphate poisoning)
Defecation/diaphoresis
Urination
Miois - excessive constriction of the pupil.
Bronchospasm/bronchorrhea (watery sputum production)
Emesis
Lacrimation
Salivation
Physiological manifestations of atropine overdose
Hot as a hare
Blind as a bat
Dry as a bone
Red as a beet
Mad as a hatter
What medication is given during colonoscopy for bowel spasms?
IV buscopan (hyoscine butylbromide) muscarinic receptor antagonist.
Similar to atropine - does not cross BBB.
Also an antiemetic (acts on CTZ), used for abdominal cramps in irritable bowel syndrome and reduce excess respiratory secretions in CP or end of life care.
Urinary incontinence management
Oxybutinin - direct antispasmodic effect on smooth muscle and inhibits muscarinic action of ACh.
(No anti-nicotinic effect at NMJ and skeletal muscle or autonomic ganglia).
If oxybutinin treatment failed- next line treatment:
Botox - multiple uses acts pre-synaptically, prevents the release of ACh = flaccid paralysis.
Treatment for acute angle closure glaucoma
Untreated this causes blindness.
Pilocarpine is a muscarinic acetylcholine receptor agonist, it constricts the pupil, opens the trabecular meshwork and increases the drainage of aqueous humor.
The increased drainage reduces the intraocular pressure preventing further damage to the optic nerve.
A surgical procedure called a trabeculectomy can be performed later to form a permanent channel for drainage
Atropine
Atropine blocks parasympathetic action.
It crosses the blood-brain-barrier and can cause confusion. Especially in the elderly.
It is used, but only in the most serious situations.
Life threatening bradycardia - 500mcg iv
It can be repeated up to 3mg if needed
If blocking parasympathetic receptors is ineffective then the next step is stimulating sympathetic ones.
If these drugs fail then electrical pacing is used.
Nicotinic antagonists
Trimethaphan (rarely used for hypertensive crisis)
Muscarinic antagonists
M1 - increases motility and secretions in the gut, CNS effects.
M2 - bradycardia, reduced contractility.
M3 - vasodilation, bronchoconstriction, pupil constriction.
Muscarinic antagonists
Atropine (crosses BBB)
Glycopyrrolate (does not cross BBB)
Hyoscine
Ipratropium (topical effect in lungs)
Nicotinic agonists
Nicotine, ACh, Neostigmine (reversible inhibitor of AChE), organophosphates (irreversible inhibitor of AChE).
Muscarinic agonists
Pilocarpine, muscarine.
ACh, Neostigmine organophosphates.
Muscle relaxants
Most muscle relaxants used in anaesthesia block the neuromuscular junction by competing with acetylcholine for nicotinic receptors.
Neostigmine blocks the breakdown of acetylcholine so its levels increase and the muscle can work again.
Acetylcholine is found in both parasympathetic nerves and the neuromuscular junction.
Neostigmine alone would have side effects of bronchospasm, bradycardia and diarrhoea.
It comes pre-mixed with glycopyrrolate which blocks all these effects.
Which of the following is false of drugs affecting the cholinergic system?
A - Botox acts on the ACh presynaptic vesicles to treat cause intentional paralysis
B - Nicotine and pilocarpine are parasympatheticomimetics
C - Pyridostigmine treats Myasthenia Gravis by inhibiting anticholinesterase
D - Atropine has minimal side effects and is safe in the elderly
E - Research on ACh re-uptake inhibitors for Alzheimer’s is still underway
A - True - Botox has an irreversible effect on exocytosis of ACh in the pre-synaptic neurone (treating spasticity, bladder instability, wrinkles!)
B- True - they are nicotinic and muscarinic receptor agonists, respectively
C - True
D - False - Atropine crosses the BBB and can cause delirium, confusion and hallucinations
E - True
Which of the following drugs does not cause an increase in heart rate:
a) Atropine
b) Adrenaline
c) Cyclizine
d) Digoxin
e) Caffeine
Answer: D digoxin is used in the treatment of tachyarrhythmias
