Peripheral Nervous System- SNS Flashcards
What adrenergic receptors are most common on vascular smooth muscle
A1
What adrenergic receptors are most common in the brain and spinal cord
A2
What adrenergic receptors are most common in myocardium
B1
What adrenergic receptors are most common in airway smooth muscle
B2
What receptors are on smooth muscle of blood vessels, direct vasodilation, and kidney?
D1 (dopamine)
What receptors are most common of post-ganglionic sympathetic nerve terminals, glomeruli, renal cortex and renal tubules, adrenal cortex, chemoreceptor trigger zone, and indirect vasodilation?
D2 dopamine
What are the direct acting sympathoMIMETICS
*Catecholamines* Epinephrine Norepinephrine Isoproterenol Dopamine Dobutamine
How should catecholamines be administered?
By injection
Absorbed from respiratory tract
Poorly absorbed after oral administration-> high first pass effect
Do catecholamines cross the BBB?
No
What is the onset and duration of Catecholamines ?
Rapid
Emergency use
What are the adverse effects of catecholamines ?
Narrow safety margin
Short half life
Predispose myocardium to tachycardia and tachyarrhythmias
Anxiety, restlessness, tremors
Altered perfusion-> direct to “flight tissue”
Extravasation of Norepinephrine or Dopamine can cause tissue damage and sloughing
Cerebral hemorrhange
What adrenergic receptor does epinephrine not have affinity for?
Dopamine
What receptor does norepinephrine not have receptor affinity for ?
B2 and Dopamine
What receptors does Isoproterneol have affinity for?
B1 and B2
What receptors does dopamine have affinity for?
Dopamine (low dose)
B1 (med dose)
A1 (high dose)
How is norepinephrine degraded/removed form the nerve endings?
Active uptake (50-80%) Diffusion Destruction -MAO= mono-amine oxidase (nerve endings) -COMT= catecholamine O-methyl transferease (tissue)
How is norepinephrine / epinephrine removed from the circulation
COMT destroy in tissues
Liver
Effects peak 10-30seconds, absent by 1 min
What is the mechanism of action of epinephrine
Direct acting catecholamine sympathomimetic
Competitive agonist at all alpha and beta receptors
Epinephrine will cause _________ at the B1 receptors
Cardiac contraction
Epinephrine will cause _________ at B2 receptors
Bronchodilation and vasodilation
Epinephrine will cause ___________ at a1 receptors
Vasocontriction
Epinephrine can be administered by what routes?
IV, IM, SQ, inhaled, IO
What are the systemic indications for using Epinephrine?
- *Cardiopulmonary arrest (CPA)
- *Anaphylaxis
- *Increase mean arterial pressure by increasing systolic arterial pressure (SAP)
Vasopressor
Positive inotrope
What local effects can epinephrine be used for?
Local anesthetic (i.e. Lidocaine) to produce regional vasoconstriction -> delay systemic absorption
Topically to treat local hemorrhage
What are precautions to using epinephrine?
Causes massive sympathetic output
-increase myocardial workload and oxygen demand
–> increased myocardial oxygen consumption (MvO2)
Can result in myocardial ischemia
Cardiac arrest is possible
What is the MOA of norepinephrine
Direct catecholamine sympathomimetic
Mainly through a1 agonism
What are the indications for using Norepinephrine ?
Vasopressor support of CV is needed
Treat hypotension
Eg. Septic shock = sepsis and hypotension leading to refractory volume expansion
What is the main clinical effect of using Norepinephrine
Vasocontriction (a1 agonist-> MOST important catecholamine vasopressors)
Less of an increase in MvO2 than with epinephrine
What re the precautions and contraindications to using Norepinephrine
Cardiac arrhythmias/ tachyarrhythias -> major adverse effect of concern
-> used cautiously and with ECG
Do not use in hypertensive patients
What is the MOA of isoproterenol
Direct acting catecholamine sympathomimetic
Potent non specific beta agonist
What are the main indications to using isoproterenol
Cardiac stimulators effects
-increase coronary, skeletal, renal, and mesenteric blood flow (positive inotropic effect)
Bronchodilation
What are the contraindications to using isoproterenol
Side effects= tachycardia, anxiety, tremors, and arrhythmias
IV infusion must be titrated to effect
ECG monitoring and BP monitoring required
What is the MOA of dopamine
Direct acting sympathomimetic
Dose-dependent effect
Dopamine receptors -low dose
Beta1 receptors- med dose
Alpha1 receptor- high dose
A low does of dopamine will have what effect?
Acts on D1 and D2 receptors
Dilation of renal, mesenteric, coronary and intracerebral vascular beds
A med-low dose of dopamine will have what effects?
Positive inotrope
A med-high dopamine dose will have what effects?
Positive chronotrope
Increase cardiac automaticity
A high dose of dopamine will have what effect
Vasoconstriction
What are the indications to using dopamine
Post-arrest vasopressor of choice
Vasopressor support
Treat hypotension due to inadequate vascular tone
What are precautions and contraindications to using dopamine
IV infusion has potential for necrosis Monitor for -tachycardia -tachyarrhythmias -change in BP
Contraindicated in hypertensive patients
What is the MOA of Dobutamine
Direct acting catecholamine sympathomimetic
B1 agonist
(Mimi also B2 and a1 agonist and NO dopamine receptor activity)
What are the main indications to using dobutamine
Patients requiring inotropic support
Treat anesthesia associated hypotension
Maintain CO and tissue organ perfusion
What are precautions to using dobutamine
Side effect= tachycardia and tachyarrhythias
Tachyphylaxis
Contraindicated with left atrial rupture or in cases where myocardial integrity is a concern
Which of the following will result in the least amount of vasodilation ? A. Epinephrine B. Norepinephrine C. Isoproterenol D. Dopamine E. Dobutamine
B. Norepinephrine
what drugs causes D1 receptor mediated vasodilation at low doses
Dopamine
What is the MOA of phenylephrine
Direct acting a1 selective agonist
What are the indications to using phenylephrine
Increase peripheral vascular resistance through systemic vasoconstriction
Treat hypotension in cats and dogs
Vasopressor effects are Short lasting (IV)
Control hemorrhange (local/topical use)
Mydriatic for open-angle glaucoma
What are the precautions and contraindications to using phenylephrine
Renal and GI vasocontriction may be undesirable
Chronic use => nasal congestion
Contradicted in hypertension
What are the non-selective Beta agonists and what are their main indications
Ractopamine and Zilpaterol
Increase rate of weight gain, feed efficiency, and Caracas leanness in food animals
What agent is primarily used as bronchodilators in treatment of lower airway diseases like asthma and COPD
Selective B2 agonist
What are the selective B2 agonists in order of most selective to least selective
Albuterol
Terbutaline
Clenbuterol
What drug would you most likely see some B1 side effects like tachycardia
A. Terbutaline
B. Albuterol
C. Clenbuterol
C. Clenbuterol
What are precautions and contraindications to using selective B2 agonists
Cardiac stimulation -> tachycardia Uterine relaxation (can cause fetal retention ).
Vasodilation
Contraindicated in patients with cardiovascular disease
What is the drug of choice for treatment of bronchial asthma?
Albuterol
Indirect/mixed sympathomimetic are mainly used for their ___________ effects
CNS
What is the main drug used for behavior modification and in old dogs for cognitive dysfunction
Selegiline
-> monoamine oxidase inhibitor (MAOI)
What is the MOA of phenylpropanolamine
Mixed (direct and indirect) sympathomimetic
Indirect increase in NE in bladder neck/urethra (primary action) and direct alpha 1 agonist
What are the indications to using Pehnylpropanolamine
Urinary incontinence due to urethral sphincter hypotonia/incompetence
What drug synergistically works with phenylpropanolamine to increase tension in the urinary spinchter
Estrogens -> upregulate a1 receptors
What are the precautions to using phenylpropanolamine
Restlessness Urine retention Tachycardia Hypertension Occasionally anorexia
What is the MOA of ephedrine
Mixed (direct and indirect ) sympathomimetic
Indirectly increase NE release and direct a1 and B activation
What are the main effects of ephedrine
CRI to maintain BP under anesthesia
Increase BP> vasoconstriction and direct cardiac stimulation
Bronchodialtion
Urinary sphincter contraction-> urinary retention
Mydriasis
What are precautions of using ephedrine
Hypertension
Arrhythmias
What are the direct acting sympatholytics ?
Phenoxybenzamine -alpha Prazosin - alpha Propranolol -non selective Beta Atenolol -selective Beta Esmolol -selective Beta
What is the MOA phenoxybenzamine
Non specific alpha antagonist
-binds irreversibly -> lasts lifetime of receptor (3-4day)
What are the indications to use phenoxybenzamine
Treat urinary retention due to urethral hypertonicity
Treat pheochromocytoma-> prior to surgery you to treat associated hypertension caused by clamping the vena cava
What are the precautions to using penooxybenzamine
Excessive alpha blockage
- hypotension
- reflex tachycardia
- miosis and change in IOP
- GI signs
What is MOA of propranolol
Non selective B-antagonist
Decrease SA firing and AV conduction
=>bradycardia and decrease CO
Increased airway resistance
T/F: Propranolol crosses the BBB
T
Significant first pass effect
Indications to using propranolol
Treat tachyarrhythmias
- > supraventriclular tachyarrhythmias
- > methylxanthine (chocolate) toxicosis
Feline hyperthyroidism
- > CV effects - arrhythmia and hypertension
- > antagonize T4->T3 conversion in peripheral tissue
Precautions to using propranolol
Bradycardia, hypotension, brochospasm
Receptor desensitization and upregulation
Contraindicated with overt heart failure, sinus bradycardia, and heart block (neg inotrope)
Contraindicated with bronchospastic lung disease (B2 effect)
What are the selective B1 antagonists and what is their effects?
Atenolol -longer half life than propranolol and more selective for B1-receptors
Esmolol -ultra short acting (rarely used)
Negative inotrope-> bradycardia
What is an indirect acting sympatholytic that blocks NE uptake into vesicles. What species is it used in?
Reserpine
Used in equine for calming
Blocked uptake =. Reduced storage and mediation depletion
What drug is used in the treatment of methylxanthine (chocolate) toxicity
Propranolol
What drug acts by inhibiting the reuptake of norepi into the presynaptic vesicles?
Reserpine
