Exam 2 Flashcards
Catecholamines are named for their
structure
General term for neurotransmitters/hormones in sympathetic NS
Catecholamines
Three major catecholamines/neurotransmitters
Dopamine, Norepinephrine, + Epinephrine
Norepinephrine is located
On effector organs at adrenergic receptors of the sympathetic NS
Four basic categories of adrenergic receptors
- Alpha 1 type (a1a,b,c)
- Alpha 2 type (a2a,b,c)
- Beta type (b1,2,3)
- Dopamine type (d1,2,3,4,5)
Adrenergic receptors (alpha1, alpha2, beta, + dopamine) are all
G-protein coupled cell membrane bound receptors
What increases of complexity of the NS by adrenergic receptors (alpha1,alpha2,beta,dopamine)
Various subtypes differing by potency + type of response
Number of factors can alter degree to which any adrenergic receptors respond to a stimulus
- Selectivity
- Regulation
- Polymorphisms
- Catecholamines
- Why we see effect in one person but not others
Receptor selectivity allows
sympathomimetic drugs to bind to one subgroup of receptors w/out binding to others
-Drug X binds to a1 receptors but not a2/B
Selective binding results in
selective actions
Degree of binding in receptor selectivity is
concentration-dependent
Receptor selectivity at low concentrations allow for
selective binding
Receptor selectivity at high concentration cause
Non-selective binding
- larger concentration floods receptors that usually don’t bind drug
- high dose of drug X bind to both a + b
- more unintended effects
Receptor regulation
Response inc./dec. over time
*usually due to changes in number of receptors/Up-down regulation
Receptor regulation can result in
Changes of observed response to sympathomimetic drugs
Example of receptor regulation
Desensitization
Desensitization AKA
- Tolerance
- Refractoriness
- Tachyphylaxis
Desensitization occurs after
long term exposure to catecholamines/drugs
Desensitization results in
Dec. responsiveness of that cell/tissue to additional stimulation
Mechanisms of desensitization
- Altered transcription/translation of DNA+/RNA
- Modifications of receptors by interaction w/enzymes/other proteins
- Long term exposure to agonist often w/ long-term drug use
- Interactions/messages from other receptors
* Results in less effect
Sometimes desensitization of receptors is the
Desired effect of drug b/c increased response followed by the desired decreased physiologic action
Example of therapeutic desensitization
Drug z binds to a1 receptors + causes exaggeration of expected physiologic response but the body doesn’t like that and wants to maintain homeostasis so the body dec. production of a1 receptors in the target organ (down regulation) so less neurotransmitter available to bind to a1 receptors result in in desired effect of drug which is dec. in a1 activity in specific target organ
All people have a and B receptors but slight changes in ______can occur in different people
amino acid sequences
Amino acid differences in receptors can
Alter receptor response
- Inc./dec. risk to develop dz
- Degree of susceptibility to desensitization
- Degree of responsive to drug
- May be why some therapeutic drugs work in some patients but not others which is a key area of future genetic investigations
Termination of neurotransmitter action
- Norepinephrine transporter (NET) protein responsible for vaccum to suck up norepinephrine
- Movement NE out of synaptic cleft + into blood stream (diffusion to area w/out receptors)
- Metabolism by catecholamine-O-methyl transferase (COMT)
- Metabolism by monoamine oxidase (MAO)
Norepinephrine Transporter (NET) targets
norepinephrine released into synaptic cleft
Major method of NE clean-up
NET removes 90% of released NE
NET acts as
a pre-synaptic pump to move NE out of synapse + back into neuron (vacuum)
Therapeutic NET
- Some drugs bind + inhibit NET action (atomoxetine (ADHD), cocaine)
- NET inhibition prolongs presence of NE in synaptic cleft increasing stimulation of adrenergic receptors
- Reverse NET action and inc. release of NE that had been taken up leading to enhanced action of NE
What metabolizes all catecholamines
Catechol-O-Methyl transferase (COMT)
What assists in terminating the actions of NE, Epi, + DA?
Cetechol-O-methyl transferase
Example of drugs that inhibit COMT + prolong the effect of catecholamines
Entacapone
What drug is used in Parkinson’s + inhibits the metabolism of levodopa, which is the precursor drug for dopamine, which is deficient in patients with parkinson’s (increases dopamine)
Entacapone
What metabolizes endogenous monoamines?
Monoamine oxidase
Examples of monoamines
NE, epi, serotonin, DA
Two forms of monoamine Oxidase
A +B
Monoamine oxidase is susceptible to _____ by many drugs which leads to ____ levels of these neurotransmitters and the ____ levels can actually be very _______
inhibition, increased, increased , dangerous
What used to be used for depression but now use SSRI’s?
Monoamine oxidase
Drugs that mimic actions of norepinephrine, epinephrine, + dopamine the three neurotransmitters?
Sympathomimetics
Sympathomimetic direct agonists
structure allows for binding to adrenergic receptors resulting in activation
Indirect agonists of sympathomimetics
Multiple mechanisms: cause release of stored catecholamines + inhibit reuptake of catecholamines already released which interferes w/ metabolism of norepinephrine
Medical chemistry of direct sympathomimetics
Able to create drugs w/ similar structural highlights to catecholamines
Provide enough similarly o be able to bind to adrenergic receptors
_____ alter affinity for a/b receptors yielding compounds w/ various levels of ____ or ____ activity in sympathomimetic drugs. This is based on where the change is out of the four key areas
Modifications, agonist, antagonist
Four key areas of sympathomimetic drugs
Benzene ring
Beta carbon
Amino group
Alpha carbon
Key focus of the pharmocological effects of sympathomimetics
Cardiovascular
pulmonary, ocular, GU, Salivary glands, apocrine, metabolism, hormone release, + CNS
Cardiovascular effects of Sympathomimetics: ___ and ____ receptors are present in the heart, blood vessels, + other systems that regulate BP.
a, B
Cardiovascular effects of sympathomimetics: Outcome of a given drug is dependent upon ____ for a + b receptors, _____ action at the receptors, action of the _______ to maintain homeostasis (desensitization)
Selectivity, pharmacologic, body’s compensatory mechanisms
*This complicates our predictions of what effect is observed when administer a drug
Key sympathomimetic effects on the cardiovascular system
Heart rate
Cardiac output
Peripheral vascular resistance
Venous return
B2 receptors of sympathomimetics in the cardiovascular system is _____ and A1 receptors ____
vasodilation, vasoconstriction (decrease/increase BP)
a1 agonist cardiovascular effects of sympathomimetics causes _____ resulting in ____ BP _____ vascular resistance which may cause a reflex _____ of HR which should ____ CO but venous return also ____ which ___ stroke volume + _____ CO (CO=HR*SV)
vasoconstriction resulting in INC BP and INC peripheral vascular resistance w
Example of an a1 cardiovascular agonist
Phenylephrine
Used to maintain BP in a pt w/ poor organ perfusions like vascular shock (IV drip for very low BP) + also used for stuffy nose by constricting blood vessels in the nasal passage ways
Phenylephrine an a1 agonist
A1 receptors are present in _____ of the cardiovascular system
vascular beds
a2 receptors are present ____ and ___ in the cardiovascular system
vascular beds, CNS
Activation of PERIPHERAL receptors by a2 agonists cause _____ but only when given_____, ______, or in very _____ doses
vasoconstriction, locally, IV push, high
Systemic administration results in activation of _____ a2 receptors which _____ sympathetic vascular tone which causes a ____ in sympathetic activity and a ___ in BP which can treat ______ (Clonidine)
central, inhibits, decreases, decrease, hypertension
Effects of B cardiovascular sympathomimetic ______ depending on which ____ receptors are activated
vary, B
B1 receptors in the heart ______ contractility + ____ HR causing an ____ in cardiac output
increase, increase, increase
B2 receptors in the VASCULATURE _____ peripheral resistance (_______) resulting in ____ BP
decrease, vasodilation, dec.
Stimulation of D1 receptors causes ______ in some areas (renal, splanachnic,coronary, cerebral)
vasodilation
Dopamine also binds to ___and ___ receptors + response is ______
a, b, dose dependant
Low dose of dopamine (<5mcg/kg/min)
activates B2 receptors causing vasodilation
Medium doses of dopamine (5-10mcg/kg/min)
activates B1 receptors increasing HR + contractility
High doses of dopamine >10mcg/kg/min activates
a1 receptors causing vasoconstriction + inc. BP
____ receptors in the lung cause ______
B2, bronchodilation
A receptors in the radial muscle of the eye cause ____ and a agonists also cause _____ outflow of aqueous humor + can _____ IOP in glaucoma
Mydriasis, inc., reduce
____ receptors in the bladder, urethral sphincter, prostate + more _____ urine retention + ______ ejaculation
A, promote, mediate
___ receptors of salivary glands ____ saliva
B, inc.
Sympathomimetics: apocrine sweat glands (palms of hands) _____ sweat production in response to ____ (not temp.)
increase, stress
Sympathomimetics ___ glycogenolysis in the liver via ____ receptors that ___ serum glucose
inc., B, inc.
___ receptors inc. lipolysis + ____ receptors dec. lipolysis
a2, b
___ receptors promote K+ uptake into cells which can cause hypokalemia
B2
___ receptors increase insulin release from islet cells, ___ decrease insulin release from islet cells
Inc., dec.
Renin has an increased release by ____ and a decreased release by ___
b1, a2
*Renin mediate renal perfusion + intravascular volume
Hormones mediated by adrenergic receptors include
Insulin Renin Parathyroid hormone Calcitonin Thyroxine Gastrin
Sympathomimetics on the CNS create feelings such as
nervousness adrenaline rush feeling of impending disaster alertness + improved attention elevation of mood Euphoria Anorexia Psychosis
Endogenous catecholamines
Epinephrine, norepinephrine, dopamine
Direct sympathomimetics
a1, a2, b1, b2 agonists
Epinephrine aka
adrenaline
Epinephrine is an agonist at ___ and ___ receptors
a, b
Epinephrine is a potent ____ + ___ stimulant due to action on a1 receptors which ____ systolic BP and ___ HR+CO via B1 receptors
vasoconstrictor, cardiac, inc., inc.
Norepinephrine aka
Noradrenaline, Levophed
Norepinephrine agonist at ___, ___, and ____ (*Minimal ____)
a1, a2, B1, b2
Norepinephrine is a potent ___+_____ stimulant
vasoconstrictor, cardiac
Low dose of dopamine
b2 receptors vasodilation
Medium dose dopamine
B1 receptors inc. HR + CO
High dose dopamine
a1 receptors vasoconstriction
Phenylephrine (Neosynephrine)
direct a1 agonist
useful decongestant + to inc. BP
Midodrine (Amantine)
Increase BP + treat orthostatic hypotension
Examples of direct a2 agonists + what they do
Clonidine (Catapres) Methylopa (aidomet) pregnancy HTN Guanfacine (Tenex) Guanabenz (wytensin) *All act in CNS to reduce BP + treat HTN
Dexmedetomidine (Precedex)
Use to use clonidine but now use this
Acts in CNS + used for sedation of patients in the ICU setting
Direct a1 + a2 drug
Oxymetazoline
a1-vasoconstriction + used as a decongestant
a2-clonidine to dec. BP (don’t usually see effects b/c local)
Nonselective B1 + B2 agonists
Isoproterenol (Isuprel)
Isoproternol
B2- vasodilation dec. dystolic BP + mean arterial pressure
B1- positive chronotropic + inotropic effects on the heart inc. HR + CO
NO ____ specific agonist
B1
B1 selective agonists ____ CO + ____ HR. An example is ____
Inc., Inc., dobutamine
Dobutamine B1 selective agonist
+ isomer-potent B1 action + a1 antagonism (blocks vasoconstriction) allowing inc. CO w/out inc. BP
- isomer- potent a1 action which inc. BP
B1 selective agonists like dobutamine when given together
the results give positive inotropic action w/ little change in BP
B2 selective agonists
Causes bronchodilation + are useful to treat asthma + COPD
Examples of B2 selective agonists
Albuterol (Ventolin) Terbutaline (brethine) Metaproterenol (alupent) Pirbuterol (maxair) Salmeterol (serevent) formoterol (Foradil)
B2 selective agonists also ____ uterine smooth muscle during premature labor (aka tocolysis)
relax
B2 selective agonists to relax smooth uterine muscle
Ritodrine (yutopar)
Terulatine
Mixed acting sympathomimetics provide ___ and ___ effects
a, b
Examples of mixed-acting sympathomimetics effects
vasoconstriction, decongestion, bronchodilation, +CNS effects such as appetite suppression, stimulation, + more
Examples of mixed acting sympathomimetic drugs
Ephedrine (performance enhancing drug)
Pseudoephedrine (Sudafed)
Ephedrine
mixed acting sympathomimetic
Obtained from multiple plant sources-herbal product ma huang (ephedra) Performance enhancing banned by WADA
Provides bronchodilation in asthma pts (better agents preferred)
Ephedra sales banned in US since 2004 due to risk of death
Pseudoephedrine (Sudafed)
Decongestion-vasoconstriction
Contraindicated in high bp
Indirect acting sympathomimetics work via two potential mechanisms
Displace catecholamines increased norepinephrine,epinephrine, + dopamine
Inhibit Reuptake of released neurotransmitter by interfering w/ NET
Examples of indirect acting sympathomimetic drugs
Amphetamines
Tyramine containing compounds (aged meats, cheeses, fish)
Catecholamine reuptake inhibitors (doluxetine)
Amphetamine causes release of stored ___ and ____. It is a _____ stimulant and ___ mood + alertness and _____ appetite
Norepinephrine, dopamine, CNS, inc., dec.
Methamphetamine (crystal meth) has a similar action to ______ made from _____ and has ____ CNS actions
amphetamine, pseudoephedrine, POTENT
Phenmetrazine has actions similar to ______
amphetamine
Methylphenidate (ritalin) is a ____ derivative used in the treatment of ____ by ___ reuptake of ____ + ____ function of the brain (smooth out norepinephrine so everything can come into focus)
amphetamine, ADHD, reduces, norepinephrine, improves
Modafinial is an _____ sympathomimetic drug that ____ Norepinephrine + dopamine transporters in the CNS. The exact mechanism is more complex + poorly understood. It is used to _____ wakefulness in pts w/ _____, ___, and ____
indirect, inhibits, increase, narcolepsy, sleep apnea, shift work disorder