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Old 04-16-2016
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Default B2 agonist confusion

Plz help with this question :
Mr. Green, a 54 year old man, had a cardiac transplant 6 months ago. His current bp is 120/70 and HR is 100 bpm.which of the following drugs would have least effect on Mr. Green's heart rate?
(A) Albutetol
(B) Epinephrine
(C) Isoproterenol
D nor epi
E. Phenylephrine
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Old 04-16-2016
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E. Phenylephrine
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Old 04-16-2016
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Originally Posted by dr.Irina View Post
E. Phenylephrine
I know this is the correct answer but can you explain why not albuterol? Its reflex tachycardia action also cannot be possible in transplanted heart.
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Old 04-16-2016
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Originally Posted by ashubutwal View Post
I know this is the correct answer but can you explain why not albuterol? Its reflex tachycardia action also cannot be possible in transplanted heart.
Yes I believe after transplantation the heart is denervated, so sympathetic response to baroreceptors (from decreased or increased BP) won't work as it would in a normal heart.
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Old 04-16-2016
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Originally Posted by hraza2222 View Post
Yes I believe after transplantation the heart is denervated, so sympathetic response to baroreceptors (from decreased or increased BP) won't work as it would in a normal heart.
But according to answer in tha katzung after transplantatio autonomic nervous system nerve is cut. It memtions that beta 1 snd beta 2 receptors go up after transplantation. so I believe b2 receptors also go up after transplantation in the heart . because both reflec bradycardia and reflx tachycardia is blocked after transplantation.
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Old 04-18-2016
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Originally Posted by ashubutwal View Post
I know this is the correct answer but can you explain why not albuterol? Its reflex tachycardia action also cannot be possible in transplanted heart.
While we say that albuterol is b2 selective, it can still activate b1 receptors. Phenylephrine only works on a1 and can only affect the heart through a reflex (as mentioned above, not possible on a denervated heart). So albuterol's expected reflex tachycardia will not be seen, but at high enough doses it will work on b1 and certainly have a greater effect than phenylephrine.
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Old 04-18-2016
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Originally Posted by Nodo View Post
While we say that albuterol is b2 selective, it can still activate b1 receptors. Phenylephrine only works on a1 and can only affect the heart through a reflex (as mentioned above, not possible on a denervated heart). So albuterol's expected reflex tachycardia will not be seen, but at high enough doses it will work on b1 and certainly have a greater effect than phenylephrine.
But I think I found several research papee stating the upregualation of b2 receptors in transplanted heart. And even the explanation in katzung states about the upregualation. so, I think upregualation part should be considered more.
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Originally Posted by ashubutwal View Post
But I think I found several research papee stating the upregualation of b2 receptors in transplanted heart. And even the explanation in katzung states about the upregualation. so, I think upregualation part should be considered more.
Yes but there are no b2 receptors in heart. The only adrenergic receptor anywhere in the heart is b1.
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