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Discussion Starter · #1 ·
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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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.:confused:
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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Discussion Starter · #5 ·
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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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.:confused:
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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Discussion Starter · #7 ·
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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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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