Adrenergic Drugs (Exam 1) Flashcards
Picture of Sympathetic (Adrenergic) and Parasympathetic (Cholinergic) Nervous System
Norepinephrine
Main adrenergic mediator (Sympathetic)
-Purpose is to maintain a constant internal environment
Epinephrine
- Also known as adrenaline
- Fight or flight
Synthesized and released from the adrenal medulla
Dopamine
Reward system contributes to survival
-Feel good, food, sex, drugs
*Abusive drugs release dopamine
Examples: amphetamine, opiates, nicotine, caffeine
Autonomic Nervous System breakdown
- CNS Outflow
- Ganglia
- Pre/post-ganglionic fiber length
- Postganglionic fiber distribution
- Response to stimulation
- Postganglionic neurotransmitter
Catecholamines (adrenergics)
Epinephrine, Norepinephrine, and dopamine
-Rapid onset of action/brief duration of action
Not orally active
Direct adrenergic agonist
Compounds that mimic the action of epinephrine
Ex. dopamine (binds to dopinergic, alpha, and beta receptors)
Indirect acting compounds
Release norepinephrine, which acts on the adrenergic receptors
Ex. amphetamine, tyramine (wine/cheese/sausage) or methylphenidate (Ritalin)
Mixed acting compounds
Have two actions:
1) Direct action to stimulate the receptors
2) Indirect action to release NE, which also acts on the receptors
Ex. pseudoephedrine (Sudafed)
What are the enzymes involved in adrenergic neurons? Cholinergic?
Adrenergic: MAO and COMT
Cholinergic: acetylecholinesterase
What is biosynthesis of catecholamines? (photo)
What is the rate limiting enzyme?
Tyrosine hydroxylase (Tyrosine to Dopa)
What can cause the accumulation of tyramine in humans?
MAO inhibitors
Consumption of food/beverages containing it (Wine/sausage/cheese)
When in the pre-synaptic neuron, what prevents MAO from breaking down all the adrenergic catecholamines (dopamine/NE)?
Dopamine and NE are stored in nerve vesicles, which prevent MAO from breaking them down
-Reserpine is an old drug that would prematurely release them from their vesicles, where they would be broken down and the neuron would be unable to release them upon arrival of an action potential (major side-effect: depression)
Catecholamine Release Sequence
Tyramine transported into a nerve ending by a Na+-dependent carrier
Converted to dopamine and transported into the vesicle by VMAT
Converted in the vesicle into NE by dopamine beta hydroxylase
NE physiologically released from nerve terminal (Dependent on Ca++ and an action potential)
What are some substances that can inhibit the recycling of NE back into the pre-synaptic neuron?
Cocaine and tricyclic anti-depressants (amitriptyline, nortriptyline, doxepin, etc.)
-Acts as an indirect agonist, inhibiting NET from bring NE back in and prolonging NE’s presence in synaptic cleft
Catecholamine Termination
Active reuptake (90%)
- NET carries NE back into the pre-synaptic neuron cell cytoplasm
Simple Diffusion (10%)
- NE diffuses into surrounding glial cells and smooth muscles, where it is eventually metabolized (plasma or liver)
What are examples of MAO inhibitors and what have they been used for?
- Phenelzine, selegiline, tranylcypromine, isocarboxazid
- Treat Parkinson’s disease (since NE/dopamine isn’t being metabolized by MAOs)
- Old treatment for depression; not used anymore
*Tyramine can cause a hypertensive crisis while using these
What should be generally associated with a1 receptors? How about ß2 receptors?
a1: Vasoconstriction
ß2: Vasodilation
Alpha1 receptor
- Location (2)
- Function (6)
Adrenergic
Located on blood vessels and smooth muscle (GI, mucosa, skin)
Control vasomotor tone (BP), vasoconstriction, pupil dilation (mydriasis)
Increased: peripheral resistance, BP, and closure of internal sphincter of bladder
Alpha2 receptor
- Location
- Function
Adrenergic
-Located at terminal ending of NE-releasing neurons
Stimulation will inhibit release of:
1) NE (via negative feedback)
2) Insulin
ß1 receptor
- Location (3)
- Function (3)
Adrenergic
- Located in Brain, heart and kidneys
1) Tachycardia - Increased:
2) Myocardial contractility
3) Renin secretion (which ultimately increases BP)
ß2 receptors
- Location (3)
- Function (7)
-Located in the lung, pancreas and smooth muscle
Vasodilation, bronchodilation, relaxed uterine smooth muscle
Slight decrease in peripheral resistance (counters a1)
Increased:
1) muscle/liver glycogenolysis
2) glucagon release
3) insulin secretion
Affinity of NE and Epinephrine for receptors (tie in Local Anesthetics)
NE: 90% alpha
Epi: 50:50* (Prefer alpha at high concentrations)
*Problematic if ß1 receptor (heart concerns)
For local anesthetics we want:
1) Localized high dose: vasoconstricts to keep LA @ site
2) Systemic low dose: minimal vasodilation/heart concerns; therefore it is critical that we have negative aspiration
Dopamine receptors
- Locations (4)
- Type and function (2)
-Located in CNS, kidney, heart and vasculature
DA1-like: control movement, cognitive function
- Positive inotropic effect (CV function; stronger contractions)
- Decreased renin and Na+ reabsorption (Decr. BP)
- Vasodilation (vasculature)
DA2-like: control movement, cognitive function, and prolactin secretion
Ropinorole
What receptor does it have affinity for? What is its function?
Ropinirole (Requip)
DA2 in brain (dopamine agonist)
Treatment of Parkinson’s and restless-leg syndrome
What is an example of a dopamine-antagonist? What is its function?
haloperidol (Haldol) and chlorpromazine (Thorazine)
Depleting DA in CNS; anti-psychotics
What are the receptor types in the eye for the radial muscle (iris) and the ciliary muscle?
Radial muscle: alpha1
Ciliary muscle: ß2