ANS Pharmacology - Kelly 1 Flashcards
ANS Pharmacology
Study of drugs that act on receptors and neurotransmitters in the ANS
Somatic NS
Controls voluntary movement of skeletal muscle
One efferent motor neuron that is cholinergic and releases ACh in the NMJ
Autonomic NS
Controls involuntary actions of internal organs and glands
Parasympathetic and sympathetic
Enteric NS
3rd division of ANS
Network of ANS neurons in the walls of the gut that regulate gut activities
Motor, secretory
Parasympathetic NS
Rest and digest
Cranial and sacral regions, ganglion are located close to target area
Slows HR and reduces BP
Simulates digestive tract to process food and eliminate waste
Controls erections
Sympathetic NS
Fight or flight Thoracic and lumber regions, ganglia located close to spinal cord Increases HR and force of contraction of heart Increases basal metabolic rate Increases sweating Widens airways to make breathing easier Decreases digestion/urination Controls ejaculation
Organization of efferent ANS
Preganglion neuron is in brain or spinal cord
Synapses on postganglionic neuron in an autonomic ganglion
Axon of postganglionic neutron innervates the target organ
Pupil regulation
Acetylcholine causes sphincter pupillae to contracts (PNS)
NE causes dilator pupille to contract (SNS)
ACh
In PNS and SNS
PNS: Pre (nicotinic) and post (muscarinic) - synaptic ganglia are cholinergic
SNS: only presynaptic ganglia (nicotinic) - post are adrenergic
Somatic: nicotinic receptor in NMJ
Adrenal medulla cells
Innervated by preganglionic fibres that release ACh and stimulate release of NE and EN
Exceptions to Sympathetic NTs
Sweat glands: nicotinic, then muscarinic
Renal vascular smooth muscle: nicotinic then dopamine
Presynaptic modulation
NT release is modulated by receptors on the presynaptic membranes of neurons
Presynaptic receptors respond to primary NT of nerve
Receptors can be positive or negative modulators of NT release
G protein coupled receptors
Gq coupled
Gi coupled
Gs coupled
Gq
Increase 2nd messengers IP3, DAG, increase Ca
Gi
Decrease cAMP, open K channel, decrease Ca influx
Gs
Increases cAMP
Ligand-gated ion channels
Nn: ganglionic
Nm: NMJ
Activation by ligand opens a cation channel and allows Na influx, depolarization
Cholinergic Agonists
Cholinomimetics, parasympatomimetic
Drugs that mimic the action of ACh at cholinergic receptors and increase parasympathetic nervous system responses
Cholinergic Antagonists
Cholinolytic, parasympatholytics
Drugs that inhibit the action of ACh at cholinergic receptors and decrease parasympathetic nervous system responses
Cholinergic Nerve
ACh is made from choline and acetyl CoA
In synaptic cleft, ACh is rapidly broken down by AChE
Choline is transported back into the axon terminal and used to make more ACh
Cholinergic Receptors
Muscarinic and nicotinic receptors
ACh binds equally with both receptor types
Muscarinic Receptors
Bind muscarine with very high affinity
Do not bind nicotine
M1, M2, M3
M1
CNS, Gq
M2
Heart, decrease HR
Gi
M3
Smooth muscle contraction, exocrine gland increased secretion
Gq
Nicotinic receptors
Nn: autonomic ganglia stimulation of SNS and PNS, Adrenal medulla release of NE, EN
Nm: skeletal muscle contraction
Muscarinic agonists
Agents that activate muscarinic receptor directly: post-synaptic receptors
Glaucoma, dry mouth, stimulate tone in bladder, increase gut motility
Non-selective muscarinic agonist
ACh
Selective muscarinic agonist
Naturally occurring alkaloids: muscarine, pilocarpine
Synthetic analogues of ACh: bethanechol
Muscarine
Can find in mushrooms
Can cross into the CNS
In periphery, mimics effects of parasympathetic nerve stimulation
Glaucoma: use of direct muscarinic agonist
Constricts ciliary muscle of eye and increase aqueous humour drainage
Uses as eyedrops
Activate M3 receptors
Side effects of muscarinic agonists
Stimulates all muscarinic receptors GI disturbances CNS effects Effects on HR Salivation and bronchoconstriction
Muscarinic competitive antagonists
Bind to muscarinic receptors preventing ACh from binding
Naturally occurring alkaloids: atropine
Synthetic analogue: ipratropium bromide
Atropine
Naturally occurring alkaloid Muscarinic competitive antagonist Dilates eye pupil for ophthalmic exam (relaxes iris sphincter and ciliary muscle) Treats bradycardia Reduces secretion during surgery
Ipratoprium bromide
Synthetic analogue
Muscarinic competitive antagonist
Treats asthma, COPD
Pilocarpine
Muscarinic agonist
Constricts iris sphincter muscle and constricts pupil
Contracts ciliary muscle to relax suspensory ligaments to increase lens thickness and refractory power
Cycloplegia
Paralysis of ciliary muscle of the eye
Bethanechol
Selective muscarinic agonist used to increase GI motility and bladder tone after surgery
Nicotinic receptor agonists
Nn and Nm
Selective Nicotinic receptor agonists
Nicotine
Used in nicotine addiction
Side effects tend to be CNS: tremor, concussions, coma
Non-selective Nicotinic receptor agonists
ACh
Nicotinic receptor antagonists
Ganglionic blockers: block Nn receptors at autonomic ganglia
Antagonists at NMJ: Nm at NJM
Depolarizing and non-depolarizing
Non-depolarizing nicotinic antagonists
Competitive
Can overcome by increase [ACh]
ie. Curare
Curare
Non-depolarizing nicotinic antagonists
Used to produce skeletal muscle paralysis during surgery and ICU
Depolarizing nicotinic antagonists
Non-competitive
Cannot overcome blockage by increase [ACh]
ie. Succinylcholine
Succinylcholine
Used to produce skeletal muscle paralysis during surgery and ICU
Cholinesterase Inhibitors
Inhibit metabolism of ACh in synapse: enhance duration of action
Mimics affect of PNS stimulation
Reversible Cholinesterase Inhibitors
Weakly bind to AChE
ie. Neostigmine, physostigmine
Loss of tone in bladder and gut, glaucoma (lowers intraocular pressure), myasthenia gravis
Myasthenia gravis
Autoimmune disease
Body makes antibodies to Nm
Want to prolong ACh at functional synapses
Irreversible Cholinesterase Inhibitors
Covalent bond with AChE - irreversible
Insecticides, nerve gasses
Effects on both N and M receptors
Initial signs muscarinic followed by central and peripheral nicotinic signs
Organophosphates
Treatment: support respiration, decontamination, muscarinic antagonist, compound that can break covalent bond with enzyme inhibitor
Adrenergic pharmacology
Antagonists and agonists
Adrenergic Agonists
Sympathomimetics, adrenergic
Mimic action of EN and NE at adrenergic receptors and increase sympathetic nervous system responses
Adrenergic Antagonists
Sympatholytics, anti-adrenergic
Inhibit action of NE at adrenergic receptors and decrease SNS responses
beta1
Predominant receptor in heart
alpha1
Important in controlling peripheral blood vessel resistance
Adrenergic nerves
Tyrosine is taken into the nerve and converted to L-DOPA by tyrosine hydroxyls
L-DOPA is converted to DA by dopadecarboxylase
DA is taken into vesicle by VMAT and converted into NE
MAO metabolizes NE in nerve that isn’t taken up
AP triggered release of NE and co-transmitter into synapse
NE/co-NT bind to pre-post synaptic receptors
NE taken up by reuptake transporter
alpha2
Presynaptic transporter
Adrenergic agonists
Drugs that mimic actions of NE by:
- Direct acting
- Indirect acting
Direct acting adrenergic agonists
Bind to pre or postsynaptic receptors
alpha1 direct acting agonists
Prototype: phenylephrine
To treat: nasal congestion, dilate pupils, combine with local anesthetics
alpha2 direct acting agonists
Presynaptic nerve terminal
Decrease NE release via inhibition of AC and cAMP signalling
ie. clonidine
Clonidine
alpha2 direct acting agonist
Used to treat hypertension, reduces SNS outflow from brain to periphery
CNS side effect: sedation
beta1 direct acting agonist
In heart
Increase force of contraction of cardiac muscle
ie. dobutamine
Dobutamine
beta1 agonist
Used to treat heart failure
Increases ability of the heart to contract: phosphorylation of Ca channels and increase Ca influx
Increase Ca can cause arrhythmias
beta2 direct acting agonist
In airway smooth muscle
Decreased contraction of smooth muscle
ie. salbutamol
Salbutamol
beta2 agonist
Used to treat asthma (relax airway smooth muscle via inhibition of MLCK phosphorylation)
Used to prevent premature labor
Side effect: increases heart rate
Indirect acting adrenergic agonists
- Inhibit NE uptake (cocaine)
2. Cause NE release (amphetamine, ephedrine)
Cocaine
Indirect acting adrenergic agonist
Used as anesthetic (blocks Na channels in nerve)
Drug of abuse
Used as topical anesthetic in nasopharyngeal surgery
Powerful CNS stimulant, increased HR, BP and force of contraction, arrhythmias
Amphetamine, ephedrine
Used to treat narcolepsy, ADHD, used as an appetite suppressant
Powerful CNS stimulant, increased HR, BP and force of contraction, arrhymias
Mechanism for amphetamine
Enters nerve terminal via NET
Competes with NE for uptake in synaptic vesicles via ventricular monoamine transporter and causes NE to accumulate in cytosol
NE is degraded by MAO and some escapes via reversal of NET transport
Competes for uptake with NE and prolongs action of released NE
Tyramine
By product of tyrosine metabolism, can be produced in high concentrations in protein-rich foods by decarboxylation of tyrosine
Metabolized by MAO in liver
Indirect sympathomimetic causing release of stored NE
Inhibition of MAO produces increased tyramine levels and release of NE
Patients taking MAO inhibitor should avoid tyramine-rich food
Direct alpha adrenergic antagonists
Block alpha receptors in the SNS
ie. Phenoxybenzamine, prazosin
Phenoxybenzamine
Direct alpha adrenergic antagonists
Non selective for alpha1 and alpha2
Decrease BP
Prazosin
Direct alpha adrenergic antagonists
Selective for alpha1 and used to treat high BP
Direct beta adrenergic antagonists
Drugs that block beta receptors in the SNS
Used to treat high BP, angina, arrhythmias, glaucoma
Side effects: exercise tolerance, asthma
ie. Proproanolol, metoprolol
Propranolol
Non selective direct beta adrenergic antagonists
Hypertension, glaucoma
Metoprolol
Cardioselective beta 1 direct beta adrenergic antagonists
Angina, hypertension
Beta-AR blockers and glaucoma
Aqueous humour is secreted by ciliary epithelium
- Passive spaces between ciliary muscle via the trabecular meshwork tissue
- Act on beta-AR receptors on epithelium and decrease aqueous humour secretion decreasing pressure in the eye