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What is the source of norepinephrine (NE) in adrenergic neurons?
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Tyrosine taken up from the diet which is then converted to L-Dopa, then Dopamine, and finally NE in vesicles.
Which enzymes are responsible for the breakdown of norepinephrine (NE)?
Catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO).
What is the function of Beta 1 (β1) receptors in the heart and kidneys?
Beta 1 (β1) receptors cause contraction, increasing heart rate (HR) and contractility.
How do adrenergic neurons release norepinephrine (NE)?
An action potential triggers voltage-gated calcium channels, leading to fusion and release of NE via exocytosis.
What clinical uses and adverse effects are associated with alpha 1 (α1) agonists?
Used for hypotension and nasal congestion. Adverse effects include reflex bradycardia and rebound congestion.
What distinguishes selective from non-selective direct agonists?
Selective agonists bind to specific receptor types, while non-selective agonists can bind to multiple types of receptors.
What are the primary receptor types for adrenergic agonists?
Alpha receptors (α1, α2) and Beta receptors (β1, β2, β3).
What are mixed adrenergic agonists and provide two examples?
These agonists show both direct and indirect actions. Examples include Ephedrine and Pseudoephedrine.
What are the clinical uses and adverse effects associated with beta 2 (β2) agonists?
Used for asthma and COPD. Adverse effects include tremors, hypokalemia, and hyperglycemia.
How is norepinephrine (NE) reabsorbed back into neurons?
Via the norepinephrine transporter (NET).
Compare the sources and receptor actions of norepinephrine (NE) and epinephrine (Epi).
Both act on α and β receptors, but NE is primarily from neurons while Epi is mainly from the adrenal medulla.
What is the mechanism of action for indirect adrenergic agonists like cocaine and amphetamines?
They inhibit NE breakdown/reuptake and increase NE vesicle release, raising NE levels in synapses.
What is the primary clinical use for beta 3 (β3) agonists and an example drug?
Used for overactive bladder. An example is Mirabegron.
What intracellular mechanism is associated with alpha 2 (α2) receptors?
Alpha 2 (α2) receptors inhibit adenylate cyclase, which decreases cyclic AMP (cAMP).
How do alpha 2 (α2) agonists function and what are their clinical uses?
They inhibit NE release and provide sedation. Clinically used for hypertension, ADHD, and withdrawal symptoms.
Describe the dose-dependent effects of dopamine as a mixed agonist.
At low doses, dopamine stimulates β1 receptors; at high doses, it affects α receptors.
How does norepinephrine (NE) affect blood pressure and heart rate?
NE increases systolic and diastolic BP and can cause reflex bradycardia, often maintaining a neutral cardiac output.
Describe the intracellular mechanisms for alpha 1 (α1) receptors.
The α1 receptors work through the Phospholipase C pathway.
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