Exam 5 - Cholinergic Antagonists & Adrenergic Receptors Flashcards
Cholinergic agonists site of action
- Pre-ganglion of adrenal medulla/sympathetic/parasymp
- Post-ganglion of parasympathetic
- skeletal muscle
Cholinergic antagonist site of action
- Same as cholinergic agonists...but in sub-groups Sub-groups: - Selective muscarinic blockers - Ganglionic blockers - Neuromuscular blockers
Cholinergic antagonist
- bind to cholinoceptors and prevent effects of Ach/cholinergic agonists
Selective muscarinic blockers
- Most clinically useful
- Block at post-ganglion of parasympathetic
- anticholinergic/muscarinic agents
- parasympolytics
- sympathetic stimulation not interrupted
Ganglionic blockers
- block nicotinic receptors of sympathetic and parasymp preganglia
- are not selective…block all ANS
Neuromuscular blockers
- block impulses to skeletal muscles
Antimuscarinics
- one of selective muscarinic blockers
- most can selectively block (except Atropine)
- block sympathetic cholinergic neurons (sweat/salivary glands)
- No action at NMJ
- No action at autonomic ganglia
Atropine
- Belladonna alkaloid
- Competitive
Actions: - eye dilation (like at eye doctor)
- GI relax
- dry mouth/ no sweat/ no tears
- high dose: increase HR (block SA node)
- low dose: decrease HR (block autoreceptors)
Uses:
- Relax GI for IBS
- treat bradycardia
- block respiratory secretions for pre-op
- antidote for organophosphate poisoning or agonist overdose
- AV block
- Pulseless electrical activity
- ENTERS CNS
Dose: 1.0 mg/ml
Scopolamine
Like atropine but…
- longer duration
- better on CNS
Uses:
- motion sickness
- nausea / vomiting
Ipratropium (Atrovent)
- Derivative of atropine
- Bronchodilator for COPD
- Inhaled
- Positive charge…can’t enter systemic circulation
Emphysema
- destruction and enlargement of air spaces
Bronchitis
- increased mucosa and inflammation
COPD
- Emphysema w/ chronic bronchitis
- Irreversible block of airflow
- smoking greatest risk factor
- therapy aimed at symptoms and prevention of progression
Benztropine (Cogentin)
- centrally acting
- treat Parkinson’s tremors
Parkinson’s Disease
- Decrease in dopaminergic activity
- leads to imbalance with cholinergic activity
- too much Ach activity in Parkinson’s
Glycopyrrolate (Robinul)
- for peptic ulcers
- pre-op to reduce secretions in mouth/throat/airway
- prevent aspiration
Adverse effects of antimuscarinics
- blurred vision
- confusion
- mydriasis (eye dilation)
- tachycardia
- constipation
- urinary retention
- bad for glaucoma (stops drainage of vitreous)
- blocks parasympathetic outflow
Atropine poisoning
- Hot as a hare
- Dry as a bone
- Blind as a bat
- Red as a beet
- Mad as a hatter
Ganglionic blockers
- block entire ANS at nicotinic receptors (symp/para preganglion)
- RARELY used therapeutically…not selective enough
Nicotine
- poison w/ no therapeutic benefit…bad for health
- no effect at NMJ
- depolarizes autonomic ganglia
- low dose: stimulate
- high dose: block
- Increases release of neurotransmitters
Neuromuscular blockers
- block Ach at NMJ
- similar to Ach and can be:
- antagonist: nondepolarizing/competitive
- agonist: depolarizing
- useful for surgery…muscle relaxation
- intubation
- lower anesthesia dose needed
- less post-op respiratory depression
Nondepolarizing neuromuscular blockers
- started as Curare….poison darts to paralyze prey
- block post-synaptic receptors (nicotinic)
- increase safety for anesthesia…but NO substitute
Mechanism:
-low dose: competitively block Ach at receptor / no depol
overcome w/ ACE inhibitors (neostigmine, edrophonuium)
-high dose: block ion channels of motor end plate
Cannot be overcome w/ ACE inhibitors - Not effective orally….IV or IM
- Cannot enter cells or BBB
Muscle recovery of Nondepolarizing blockers
- Face/eye (first to paralyze)
- Fingers/limbs/neck/trunk
- Intercostals
- Diaphragm
- Recover in reverse order
Nondepolarizing blockers drug interactions
- Cholinesterase inhibitor: antagonize effect if not in ion channel
- Halogenated hydrocarbon anesthetics: enhance
- Aminoglycoside antibiotic: enhance effect
- Ca channel blockers: enhance effect
- Last two block Ca from entering neuron
Nondepolarizing blocker drugs
- Vecuronium 45 min - Cisatracurium (Nimbex) 90 min - Pancuronium (Pavulon) 90 min - Rocuronium (Zemuron) 45 min
- decrease O2 consumption on CPB…Venous sats will tell
Nondepolarizing blocker reversal drug
Sugammadex (Bridion)
- reverses Roc / Vecuronium / Pancuronium
- does not inhibit ACE
- no cholinergic side effects
- surrounds blocker and prevents its interaction
Depolarizing neuromuscular blocker
- Depolarize muscle fiber like Ach
- resistant to ACE and remains attached to receptor
- constant stimulation and persistent depolarization
- prevents repolarization
- removed by psuedocholinesterase in plasma (not at NMJ)
- patient will convulse first….then paralyzed
Succinylcholine (Anectine)
- Sux
- rapid onset (good for intubation)
- last only minutes
- IV
- Respiratory muscles last to be paralyzed
- May cause muscle soreness (initial convulsions)
- can deliver nondepolarizer first to help with this
Side effects:
- Hyperthermia (can induce malignant hyperthermia)
- Apnea (in Persian Jews / Indian Hindu)
- Hyperkalemia (increased K)
- burn patients susceptible
Malignant hyperthermia
- extra metabolism in muscles….life threatening
- inherited disorder
- triggered by sux and volatile anesthesia
- increase CO2 / heat production
- activates SNS
- DIC: disseminated intravascular coagulation
- multiple organ dysfunction
- death
Depolarizing vs Nondepolarizing blockers
- Depolarizing cause persistent contraction…NonD stop depolarization altogether
- Depolarizing paralyze large muscles -> short -> resp
NonD paralyze short muscles -> large -> resp - Depolarizing irreversible…NonD reversible
- Depolarizing stimulate first, then flaccid…NonD just flaccid
Antimuscarinics
- Atropine
- Glycopyrrolate (Robinul)
- Benztropine (Cogentin)
- Scopolamine
- Ipratropiuim (Atrovent)
Ganglionic Blcokers
- Nicotine
Nondepolarizing NM Blcokers
- Vecuronium
- Cisatracurium (Nimbex)
- Pancuronium (Pavulon)
- Rocuronium (Zemuron)
Nondepolarizing NM Blocker Reversal
- Sugammadex (Bridion)
Depolarizing NM Blocker
- Succinylcholine (Anectine)
NE
- primary transmitter released by adrenergic neurons
- CNS and sympathetic
Epi
- released from adrenal medulla as hormone
Sympathomimetics
- drugs that activate adrenergic receptors
- can be direct or indirect acting
Sympatholytics
- drugs that block activation of adrenergic receptors
Steps of adrenergic neurotransmission
- similar to cholinergic, except NE is neurotransmitter Steps: - synthesis - storage - release - receptor binding - removal - metabolism
Step 1 of NE transmission
- Tyrosine is co-transported into neuron
- Tyrosine converted to DOPA (via tyrosine hydroxylase)
- RATE LIMITING
- DOPA converted to dopamine inside neuron
Step 2 of NE transmission
- Dopamine moved into vessicle
- Dopamine into NE (via dopamine B-hydroxylase)
- step inhibited by Reserpine
Step 3 of NE transmission
- Action potential causes influx of Ca
- Vessicle fuses w/ membrane
- Exocytosis release NE and cofactors into synapse
- Release blocked by Guanethidine
Step 4 of NE transmission
- NE binds to receptors on effective organ and auto-receptors
- NE is metabotropic….2nd messenger system
Step 5 of NE transmission
NE removed from synapse via:
- diffuses out
- taken back into neuron
- metabolized by COMT into inactive metabolites into urine
Step 6 of NE transmission
- COMT metabolizes in cleft
- MAO metabolizes once taken back into neuron
- Both convert to inactive metabolites into urine
Adrenergic receptor location
- post-synaptic ganglia of sympathetic and adrenal medulla
Alpha adrenoreceptors affinity
Epi
NE
Isoproterenol
- High down to low…EPI/NE much higher than Iso
- divided into a1 and a2
Beta adrenoreceptor affinity
Isoproterenol
Epi
NE
High down to low…Iso much higher than Epi/NE
Divided into B1/B2/B3
Alpha 1 adrenoreceptor
- high affinity for phenylephrine
- mostly affects vasculature
- postsynaptic membrane of effector organ
- Smooth muscle constriction (adrenergic effects)
- activates G-protein 2nd messenger systems
- DAG: turns on other proteins
- IP3: release of Ca into cytosol
- further divided into A/B/C/D
Alpha 1 effects
- increase vascular tone -> increase BP
- increase PVR
- mydriasis
- increase bladder tone
- increase tension in prostate
- Think fight or flight
Alpha 2 adrenoreceptors
- high affinity for clonidine
- affects CNS feedback loops for HTN and sedation
- sympathetic PREsynaptic nerve ending (also PRE para)
- control release of NE (inhibitory autoreceptors)
- effect mediated by inhibition of adenylyl Cyclades / drop in cAMP
- divided into A/B/C
Alpha 2 effects
- blocks NE release / sympathetic tone
- blocks Ach release
- blocks insulin release
- used as sedative in CV surgery
B1 adrenoreceptor
- Equal affinity for NE/Epi (both much less than iso)
- major role on heart
B1 effects
- tachycardia
- increase contractility
- increase in renin from kidneys (increase BP…hold water)
- increase in lipolysis (for energy)
B2 adrenoreceptors
- higher affinity for EPI over NE
- mostly in lungs
B2 effects
- relaxation of pulmonary smooth muscle (airway open)
- vasodilation of skeletal muscles (more flow)
- decrease PVR
- increase glucagon release (for energy)
- uterine muscle relaxation
B3 adrenoreceptors
- involved in lipolysis
- effects muscles of bladder
- not big player
Dopaminergic Receptors
5 subtypes:
- D1/D2: peripheral mesenteric and renal beds
- D2: presynaptic adrenergic neurons
- Dopamine can bind to all other adrenergic receptors (a/B)
- interfere with release of NE
Dopamine sites of action:
- brain
- renal/visceral arterioles (dilation/natriuresis…Na in urine)
- CV system (activate B receptors…HR/contractility up)
- Vascular PVR (up or down depending on dose)
Receptor desensitization
- prolonged exposure to catecholamines reduces responsiveness (NE/Epi/Dopa) Via: - sequestration of receptors - down-regulation - deactivation of G protein