catecholamines pcol exam 3

Which dopamine receptor subtype is linked to Gs proteins and causes smooth muscle relaxation

D1 receptors (Gs-coupled) → ↑cAMP → smooth muscle relaxation (vasodilation)

What happens to cAMP and vascular tone when D1 receptors are activated

cAMP increases, vascular tone decreases (vasodilation)

Why is dopamine used in heart failure with oliguria

Activates D1/D2 receptors → renal vasodilation → increased renal perfusion and urine output

Which receptors are activated at low, moderate, and high dopamine infusion rates

Low: D1/D2; Moderate: β1; High: α1 (progressive activation)

Can dopamine cross the blood-brain barrier

No — it’s too polar; L-DOPA is used for CNS effects

What receptor does fenoldopam activate and what is it used for

Selective D1 agonist used for hypertensive emergencies; causes arteriolar vasodilation and natriuresis

What does raising cAMP in vascular smooth muscle cause

Smooth muscle relaxation → vasodilation → ↓TPR

What is the mechanism of reserpine in lowering BP

Irreversibly blocks VMAT → prevents NE/DA/EPI storage → depletion → ↓sympathetic tone

What is the normal function of VMAT

Transports NE, DA, EPI, and serotonin into synaptic vesicles for storage and release

How does metyrosine work and what is it used for

Inhibits tyrosine hydroxylase → ↓DA, NE, EPI synthesis; used in pheochromocytoma

Which receptors are primarily activated by norepinephrine

α1, α2, β1

Which receptors are primarily activated by epinephrine

α1, α2, β1, β2

What is the reflex response to α1-mediated vasoconstriction by NE

↑BP triggers baroreceptor reflex → reflex bradycardia (↑vagal tone)

What are NE’s effects on TPR and HR

↑TPR (α1 vasoconstriction), ↓HR (reflex bradycardia)

What are EPI’s effects on TPR and HR

↓TPR (β2 vasodilation > α1 constriction), ↑HR (β1 stimulation)

What is norepinephrine used for clinically

Shock, hypotension, septic shock (pressor to raise BP)

What is epinephrine used for clinically

Anaphylaxis, cardiac arrest, asthma; prolongs local anesthetics

How does epinephrine help in anaphylaxis

β2: bronchodilation; α1: reverses vasodilation/edema; β1: supports CO

What happens when epinephrine is given with propranolol

β-blocked → α1 unopposed → vasoconstriction → ↑BP → reflex bradycardia

What happens when epinephrine is given with prazosin

α1 blocked → β2 unopposed → vasodilation → ↓BP → reflex tachycardia

What is “epinephrine reversal”

After α1 blockade (e.g., prazosin), epinephrine causes vasodilation instead of constriction (BP ↓)

What type of antagonism occurs between histamine and epinephrine in anaphylaxis

Physiologic antagonism: epinephrine reverses histamine-induced bronchoconstriction and vasodilation

What are the main pressor agents among catecholamines

Norepinephrine, epinephrine, dopamine (dose-dependent), and phenylephrine

Which receptor type mediates the reflex bradycardia seen with NE

Baroreceptor reflex via vagus nerve (↑parasympathetic output)