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Questions and Answers
Which type of adrenergic agonists work by promotion of norepinephrine release?
What is the defining feature that differentiates catecholamines from noncatacholamines?
Why can't catecholamines be used orally?
Which enzyme quickly metabolizes catecholamines?
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What is the mechanism of action for direct adrenergic agonists?
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What class of adrenergic agonists cannot cross the blood-brain barrier?
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Which group contains dopamine, epinephrine, isoproterenol, and ephedrine?
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Which enzymes are present in the liver and in the intestinal wall?
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Why are catecholamines ineffective when given orally?
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What causes the pink or brown pigmentation of catecholamine-containing solutions over time?
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How do noncatecholamines differ from catecholamines in terms of metabolism?
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What allows noncatecholamines to be given orally?
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Why do noncatecholamines have longer half-lives compared to catecholamines?
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What makes noncatecholamines less polar than catecholamines?
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Study Notes
Adrenergic Agonists
- Alpha-2 agonists work by promoting norepinephrine release.
Catecholamines
- Defining feature: presence of a catechol group (3,4-dihydroxyphenyl) in their structure.
- Cannot be used orally because they are rapidly metabolized by COMT (catechol-O-methyltransferase) and MAO (monoamine oxidase).
- COMT quickly metabolizes catecholamines.
Mechanism of Action
- Direct adrenergic agonists work by directly binding to adrenergic receptors.
Classification
- Catecholamines: dopamine, epinephrine, isoproterenol, and ephedrine.
- Noncatecholamines: cannot cross the blood-brain barrier.
Enzymes
- COMT and MAO are present in the liver and intestinal wall.
Ineffective Oral Administration
- Catecholamines are ineffective when given orally due to rapid metabolism by COMT and MAO.
Pigmentation
- Catecholamine-containing solutions turn pink or brown over time due to oxidation.
Metabolism
- Noncatecholamines differ from catecholamines in that they are not metabolized by COMT.
Oral Administration
- Noncatecholamines can be given orally because they are not rapidly metabolized by COMT and MAO.
Half-Lives
- Noncatecholamines have longer half-lives compared to catecholamines due to slower metabolism.
Polarity
- Noncatecholamines are less polar than catecholamines, making them more capable of crossing the blood-brain barrier.
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Description
Test your knowledge on adrenergic agonists and the mechanisms of adrenergic receptor activation, including direct and indirect agonists. Learn about the effects of these drugs and how they mimic sympathetic nervous system activation.
