ANS and Pharmacokinetics -- 10.1 & 10.2 Flashcards
Describe some characteristics of the parasympathetic nervous system
Long, myelinated pre-ganglionic neurones
Short unmyelinated post-ganglionic neurones
Oppose sympathetic actions
Originate in medulla and sacral regions
Ganglia located in tissue innervated by para. fibres
Describe some characteristics of the sympathetic nervous system
Short, myelinated pre-ganglionic neurones
Long, unmyelinated post ganglionic neurones
Ganglia located close to spinal cord in paravertebral cord
Fight or flight response
Originate from lumbar and thoracic vertebrae
What type of neurones are pre-ganglionic neurones?
Cholinergic
– ACh
What type of neurones are parasympathetic post-ganglionic neurones?
Cholinergic with muscarinic AChR
G protein coupled
What type of neurones are sympathetic post-ganglionic neurones?
Noradrenergic with alpha 1 and beta 1 adrenoceptors
G protein coupled
Which receptors are G protein coupled?
M1, M2, M3, alpha1, alpha2, beta1, beta2, eta3
What type of transmitters are used for sweat gland and follicle innervation?
Non-adrenergic, non-cholinergic transmitters (NANC) transmitters
e. g. nitric oxide, ATP, 5-hydroxytryptamine (seratonin)
- - Usually co-released with NA or ACh
Describe the sympathetic innervation in adrenal glands
Have chromaffin cells
“postganglioninc sympathetic neurons that do not project to a target tissue”
Stimulated by nAChR which causes the release of adrenaline in to the bloodstream
What is familial dysautonomia?
Autosomal, recessive disorder affecting the development and survival of
sensory, sympathetic and (some) parasympathetic neurones
Symptoms of familial dysautonomia?
Dysautonomic crises - response to physical or emotional stress included vomiting, increased HR and BP, sweating and drooling
Spinal curvature
Poor growth
Cardiovascular and respiratory dysfunction
Altered sensory perception
Why are cholinergic therapeutic interventions not commonly used?
The drugs are not very selective for their target receptors, so multiple side effects ail arise.
What do acetylecholinesterase inhibitor do?
Enhance the effects of acetylcholine
e.g. pyridostigmine in myasthenia gravis
donepezil in Alzheimers
What are some possible side effects for cholinergic drugs?
Bradycardia and decreased cardiac output
Increased bronchoconstriction in smooth muscle
Increased peristalsis
Increased sweating and salivation
How are some cholinergic drugs used clinically?
Are administered locally in order to limit side effects and increase effectivity
Describe some mAChR agonists
Pilocarpin and bethanechol for glaucoma and to stimulate bladder emptying
Describe some mAChR antagonists
Ipratropium and tiotropium for asthma and COPD
Tolterodine for overactive bladder
What type of receptors do you usually find in post-ganglioninc sympathetic neurones?
Noradrenergic
What is a particular characteristic of innervation around smooth muscle?
A highly branched axonal network with variscosities (beads along axons) overlies the entirety of smooth muscle. These are specialised for Ca2+ dependent noradrenaline release
How is noradrenaline synthesised?
Tyrosine to DOPA (tyrosine hydroxylase)
DOPA to dopamine (DOPA carbosylase)
Dopamine to noradrenaline (dopamine beta-hydroxylase)
Where does noradrenaline synthesis take place?
Takes place in variscosities over smooth muscle cells. Tyrosine to dopamine stage takes place in cell cytosol whilst dopemine conversion to noradrenaline takes place in vesicles
How is noradrenaline removed from post-synaptic adrenoceptors?
Noradrenaline transporter proteins
What are the two methods of re-uptake of noradrenaline?
Uptake One
– uses Na+ dependent, high affinity transports to take NA back into presynaptic cells (takes place for majority of noradrenaline)
Uptake Two
– uses a lower affinity, non-neuronal mechanism for NA not taken up by uptake one, into the post-synaptic cells
Describe NA metabolism
Some NA which has been brought back into the cell is taken up by vesicles.
The NA which has not been taken up by vesicles is metabolised by:
Monoamine oxidase (MAO)
Catechol-O-methyltransferase (COMT)
What regulates the release of noradrenaline?
Inhibition and activation of Ca2+ dependent exocytosis
– inhibit VOCCs
less Ca2+ in the cell leads to less neurotransmitter release
What are the classes of drugs that have an effect on adrenergic receptors?
Indirectly acting sympathomimetic agents
and
Uptake One inhibitors
Describe “indirectly acting sympathomimetic agents”
The drug is taken up into the synaptic vesicles and cause NA to leak from those vesicles.
NA then leaks into the synaptic cleft without being exocytosed.
– They mimic the actions of sympathetic transmitters (allows them to be taken up into vesicles)
E.g. Tyramine, amphetamine (rapidly penetrates blood-brain barrier – drug of abuse), ephedrine
Describe “uptake one inhibitors”
Inhibit the re-uptake of noradrenaline into the pre-synaptic cells
eg. Tricyclic antidepressants and selective noradrenaline re-uptake inhibitors
Where do uptake one inhibitors have their main effect and what side effects can they causes?
How can these side-effects be limited?
Mostly effect the CNS
Can cause tachycardia and cardiac dysarrythmias
– minimised by the specific drug used and the therapeutic dose of the drug
Name two beta2 selective agonists and describe what they do
Salbumatol and salbumetrol
Activate bronchodilation in the lungs by opposing bronchoconstriction
What is the advantage of selectivity of drug for certain receptors?
Specificity of drug action to limit side effects in other parts of the body
What is the purpose of alpha 1 selective and beta 1 selective antagonist?
Treat CVS disorders such as hypertension
Alpha one – doxazosin
Beta one – atenolol
What drugs are usually combined to treat congestive heart failure?
Diuretic (lower blood volume & BP) ACE inhibitor (reduce fluid retention) Beta blocker (reduces force of contracion and cardiac output)
