Cardiology Pharmacology, Part II: Alpha & Beta Receptors

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Where is the a1 receptor located?
On the postsynaptic membrane of effector organs, like vascular smooth muscle

Where is the a2 receptor located?
on the presynaptic nerve endings, like in smooth muscle

What is the downstream mechanism of the a1 receptor?
1 – couples to Gq
2 – GTP activates dissociation of alpha subunit
3 – binds and activates PLC
4 – activates DAG (–> PKC) and IP3 (–> other protein kinases

What is the downstream mechanism of the a2 receptor?
1 – couples to Gi
2 – alpha subunit inhibits GTP
3 – inhibition of cAMP
4 – slows down or inhibits vesicle release

What is the downstream mechanism of the β receptor?
1 – couples to Gs
2 – stimulates adenylyl cyclase
3 – increased production of cAMP
4 – biologic effect

Does B1 have a greater affinity for NE or Epi?
It has equal affinity for NE and Epi

Does B2 have a greater affinity for NE or Epi?
Epinephrine

What are the major effects of the a1 receptor?
– vasoconstriction
– increased peripheral resistance
– increased blood pressure
– mydriasis
– increased closure of internal sphincter of bladder

What are the major effects of the a2 receptor?
– inhibition of NE release (as an autoreceptor)
– inhibition of Ach release (as a heteroreceptor)
– inhibition of insulin release

What are the major effects of the B1 receptor?
– tachycardia
– increased lipolysis
– increased myocardial contractility
– increased release of renin

What are the major effects of the B2 receptor?
– vasodilation
– slight decrease in peripheral resistance
– bronchodilation
– increased muscle and liver glycogenolysis
– increased release of glucagon
– relaxed uterine smooth muscle

Which receptor causes arterial and venoconstriction on the cardiovascular system?
alpha-1 adrenergic receptor

Which receptor causes local vasoconstriction on the CV system?
alpha-2 adrenergic receptor

Which receptor causes increased contractility, stimulattion of SA node, and cardiac output to the heart?
Beta-1 adrenergic receptor

Which receptor causes decreased peripheral resistance and vasodilation on the vasculature?
Beta-2 adrenergic receptor.

Epinephrine
Direct alpha (high doses) and beta (low doses) receptors; agonist

Norepinephrine
Direct a1, a2, B1 agonist

Phenylephrine
Direct a1 agonist

Midodrine
Direct a1 agonist

Clonidine
Direct a2 agonist

Methyldopa
Direct a2 agonist

Guafacine
Direct a2 agonist

Guanabenz
Direct a2 agonist

Oxymetazoline
Direct non-selective alpha agonist

Dobutamine
Direct B1 agonist

Isoproterenol
Direct non-selective Beta agonist

Ephedrine
Direct mixed agonist

Psuedoephedrine
Direct mixed agonist

Cocaine
Indirect agonist

Amphetamine
Indirect agonist

Tyramine
Indirect agonist

What are the major effects of an alpha antagonist?
– lowers peripheral vascular resistance
– determines arteriolar and venous tone of vascular smooth muscle
– good for primary hypertension

What are the major effects of a Beta antagonist?
– lower blood pressure and negative chronotropic and ionotropic effects
– slowed AV conduction with increased PR interval
– opposes B2 vasodilation
– may increased TPR with unopposed a-receptor mediated effects
– inhibition of lipolysis

Phenoxybeazamine
Non-selective alpha antagonist

Phentolamine
Non-selective alpha antagonist

Group: Aozsins

What drugs are included in this group?

a1 antagonist (includes prazosin, terazosin, doxazosin)

Tamsulosin
a1 antagonist

Propanolol
Non-selective Beta antagonist (but B1 > B2)

Metropolol
B1 antagonist

Atenolol
Not sure

Pindolol
Non-selective beta partial agonist

Labetaolol
Non-selective beta (and some alpha) antagonist

Carvedilol
Non-selective Beta antagonist

Esmolol
B1 antagonist

What are the side effects of alpha receptor blocks (list two)
– postural hypotension
– reflex tachycardia

What are the side effects for beta receptor blocks (list 8)?
– increased triglycerides in plasma
– lowered HDL
– depresses myocardial contractility and excitability
– severe hypotension
– bradycardia
– heart failure
– fatigue
– exercise intolerance

What are contraindications for alpha receptor adrenergic drugs?
– hypertension
– patients receiving nonselective beta blockers
– caution with patients with CVD
– cardiac tachyarrythmias

What are the contraindications for beta receptor anti-adrenergic drugs?
– asthma
– nodal dysfunction in SA or AV node
– diabetic patients

What are contraindications for Beta-2 receptor adrenergic drugs?
– hypotension
– cardiac arrhythmias

What are contraindications for Beta-1 receptor adrenergic drugs?
– hypertension
– beta blockers

A patient has been diagnosed with hypertension. Which receptor medications would you likely use for treatment?
– alpha receptor antagonist
– Beta receptor antagonist (mostly B1)
– a2 agonist
– B2 agonist (maybe)

A patient has been diagnosed with congestion (non-allergenic). Which receptor medications would you likely use?
– a1 agonist
– non-selective alpha agonist
– B1 agonist

A patient has been diagnosed with asthma. Which receptor medications would you use to treat it?
– B2 agonist

A patient has been diagnosed with hypotension. Which receptor medications would you likely use for treatment?
– direct acting a1 agonist

A patient has been diagnosed with cardiac arrhythmias (supraventricular or ventricular). Which receptor medications would you likely use for treatment?
– B1 antagonist

A patient has been diagnosed with congestive heart failure. Which receptor medications would you likely use for treatment?
– B1 antagonist

A patient has been diagnosed with acute heart failure. Which receptor medications would you likely use for treatment?
Beta-receptor agonist

A patient has been diagnosed with cardiac arrest. Which receptor medications would you likely use for treatment?
B2 agonist

A patient is in anaphylactic shock. What chemical/drug would you use?
Epinephrine

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