Adrenergics Flashcards
Where do you find Alpha 1 receptors and what do they do?
Generally they CONSTRICT.
You find them in blood vessels and sphincters. They are also in charge of ejaculation and orgasm and the contractions of labor.
Where do you find Beta 2 receptors and what do they do?
Generally they DILATE.
You find them in blood vessels. They are also in charge of uterus relaxation and DECREASED GI motility and tone.
(decreased uterine motility/tone during labor)
Where to you find Beta 1 receptors and what do they do?
You find them in the heart (“B my number 1”)
They are in charge of the heart’s fight or flight response: increased heart rate (SA and AV nodes), increased contractility, increased renin release in the kidneys.
How are norepinephrine and epinephrine synthesized?
Dietary Tyrosine into sympathetic neuron transporter --> Dopa --> Dopamine into vesicle --> Norepinephrine --> Epinephrine (adrenal medulla only!)
How is Norepinephrine regulated?
Calcium entry –> NE release from neuron to synapse
Inhibited by Alpha 2 and Prostaglandin E2 receptors
Enhanced by Angiotensin II in its receptors
How are catecholamines metabolized?
MAO and COMT metabolize them in the liver, kidney and GI tract
MAO is also in the presynaptic terminals of noradrenergic neurons.
What happens to extra norepinephrine?
90% of extra NE in the synapse is taken up/recycled by the NE transporter (NET)
Extra NE in the cell is stored in vesicles for later or metabolized by MAO.
What do adrenergic agonists do, and name some examples
Short term: they activate alpha and beta receptors
Chronic: they desensitize/downregulate the receptors
Examples: phenylephrine, isoproterenol
What to adrenergic antagonists do, and name some examples
Short term: block alpha and beta receptors
Chronic: super-sensitize/up-regulate receptors
Examples: phentolamine, propranolol
What are four ways that the chemical structure of a drug can predict its action?
- Increasing SIZE of the amino group tail will increase Beta receptor affinity (eg: Isoproterenol)
- Hydroxyls at positions 3 and 4 will cause alpha and beta activity (eg: catecholamines)
- Removing hydroxyls will increase CNS penetration (eg: ephedrine, amphetamine)
- Noncatecholamines are NOT metabolized by COMT, and a substitution of the alpha carbon will also stop MAO metabolism (thereby increasing half-life)
Which catecholamine prefers alpha 1 and beta 1 receptors? (Which one “likes the 1s”?)
Norepinephrine
Which catecholamine prefers Beta 1 and Beta 2 receptors (“likes the betas”)?
Isoproterenol
Which catecholamine is nonselective/promiscuous for the alpha and beta receptors?
Epinephrine
Low doses: B1=B2>A1
Hi doses: B1=B2=A1
Which catecholamine is very promiscuous for all receptors at a high dose?
Dopamine
Low doses: DA>B1>B2
Hi doses: DA=B1=B2=A
Which drug is selective for contractility at low doses?
Dobutamine
Low doses: B1»>B2
Hi doses: B1»B2=A1
Which catecholamine will increase heart rate and decrease blood pressure at a low dose, but increase blood pressure at a high dose?
What is this used for?
Dopamine will increase heart rate (B1) and decrease blood pressure at a low dose (DA, B2), but increase blood pressure at a high dose (A1)
Used for shock, especially cardiogenic.
Which catecholamine will initially increase systolic BP but decrease diastolic BP?
What is this used for?
Epinephrine will initially increase systolic BP (B1 increases HR) but decrease diastolic BP (B2 vasodilation decreases total peripheral resistance and thus diastolic BP). Later A1 will “win” over B2, cause vasoconstriction and increases diastolic BP.
Used for anaphylaxis, asthma (bronchodilation), cardiac arrest (B1 stimulation), topical hemostasis (shrinks mucosa of nose/throat/larynx for surgery)(alpha 1 vasoconstriction)
Which catecholamine will increase heart contractility but not affect the heart rate?
What is this used for?
Dobutamine due to its selectivity for B1 at low dose (with some A1 and B2 at high dose).
Used for heart failure re open heart surgery, acute MI