DrVirgo
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26. Which of the following drugs produces vasoconstriction that is not blocked by prazosin and bradycardia that is blocked by scopolamine?
A
) Amphetamine
B
) Angiotensin
C
) Norepinephrine
D
) Phenylephrine
C> Norepi...
alpha 1--> VC --> Inc. TPR---> Inc. MAP--> Reflex Bradycardia (via Beta 1)?.
Would Prazosin (alpha 1 blocker) block the VC?
Scopolamine (muscarinic blocker) would NOT block the relfex bradycardia
What are the actions of the other choices?
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| robin082006
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B
Angiotensin causes direct vasocontriction---> increases BP--> reflex bradycardia.
Direct vasocontriction is not blocked by Prazosin.
Reflex Bradycardia (parasympathetic activation) is blocked by scopolamine.
Other choices: A and D cause tachybradia, C causes vasocontriction but blocked by prazosin.
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| r_albayunen
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 hmm
ill go with A
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| krsna
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B is right i thnk
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| yasmeen
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B IS RIGHT GO THROUGH KAPLAN PHARMA MANY QS LIKE THIS
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| r_albayunen
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ok .. let say that amphetamines enhances the release of NE from mobile pool .. NE go to its alpha 1 to promote VC .. why would prazozin not blocke it?????
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| yasmeen
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THAT IS WHY AMPHETAMINE IS WRONG Q IS EXEPT
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| mjl1717
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this is how Id think (after the fact). angio II- potenet vasoconstrictor has its own Angio II receptor, causing a reflex bradycardia blocked by the muscarinic anticholinergic scopolamine. the other distractors have something to do with alpha 1 agony hope this helps. comments??
Edited by mjl1717 on 05/03/06 - 06:31 AM
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| DrVirgo
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You guys are right its B... I was reading the question wrong.... 
Here is the complete mechanism as I understand it:
Angiotensin-1 works on AT-II Receptors!
This causes vasoconstriction which increases TPR and Increases MAP...
This causes a reflex bradycardia.
The VC CANNOT be blocked by Prazocin (an alpha blocker), because the VC was not caused by alpha-1 stimulation to begin with.
Scopolamine (a muscarinic antagonist) CAN block the reflex bradycardia by acting on the M2 receptors of the heart.
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