Propranolol causing bronchodilation and vasodilation?

[Rogue_Leader]

---

Members do not see this ad.

I got Lange's Pharmacology cards and was flipping through the cards and I got to the Propranolol card. This is what is says under the mechanism of action

"Propranolol is a B1 and B2 receptor antagonist. By blocking the B1 receptor, HR and contractility are decreased, thereby leading to decreased cardiac output. By blocking the B2 receptor, vascular and respiratory smooth muscle constriction is decreased, which results in peripheral vasodilation as well as bronchodilation."

That part about B2 receptor antagonism causing vasodilation and bronchodilation seems totally wrong, and I was willing to write it off as a publishing error, however on the same card it lists bronchoconstriction as a side effect, so that got me thinking that maybe there's some kind of reflex vasodilation that I can't think of. Any thoughts on what's correct?

 

[JulianCrane]

Propranolol should bronchoconstrict because of the B2 blockade. This is why it should not be given to an asthmatic. Remember, that generally whatever vasodilates in the systemic vasculature will cause vaso/bronchoconstriction in the pulmonary vasculature. One reason that propranolol causes vasodilation is because it works on B1 receptors to slow down heart rate and contractility of the heart to lead to a decreased afterload, aka, blood pressure. Hope that helps.

 

[mickdogg81]

I got Lange's Pharmacology cards and was flipping through the cards and I got to the Propranolol card. This is what is says under the mechanism of action

"Propranolol is a B1 and B2 receptor antagonist. By blocking the B1 receptor, HR and contractility are decreased, thereby leading to decreased cardiac output. By blocking the B2 receptor, vascular and respiratory smooth muscle constriction is decreased, which results in peripheral vasodilation as well as bronchodilation."

That part about B2 receptor antagonism causing vasodilation and bronchodilation seems totally wrong, and I was willing to write it off as a publishing error, however on the same card it lists bronchoconstriction as a side effect, so that got me thinking that maybe there's some kind of reflex vasodilation that I can't think of. Any thoughts on what's correct?

B2 adrenergic/sympathetic receptor stimulation in the bronchial smooth muscle normally produce vasodilation.....block the B2 with non-selective beta-blocker=vasoconstriction. Bronchial B2 receptors do basically the oppo of what B2 receptors normally do to skeletal blood vessels (dilate).

 

[Rogue_Leader]

Propranolol should bronchoconstrict because of the B2 blockade. This is why it should not be given to an asthmatic. Remember, that generally whatever vasodilates in the systemic vasculature will cause vaso/bronchoconstriction in the pulmonary vasculature. One reason that propranolol causes vasodilation is because it works on B1 receptors to slow down heart rate and contractility of the heart to lead to a decreased afterload, aka, blood pressure. Hope that helps.

Wouldn't the decreased CO cause a sympathetic baroreceptor reflex with peripheral vasoconstriction through A1 receptors?

 

[seasurfer]

I got Lange's Pharmacology cards and was flipping through the cards and I got to the Propranolol card. This is what is says under the mechanism of action

"Propranolol is a B1 and B2 receptor antagonist. By blocking the B1 receptor, HR and contractility are decreased, thereby leading to decreased cardiac output. By blocking the B2 receptor, vascular and respiratory smooth muscle constriction is decreased, which results in peripheral vasodilation as well as bronchodilation."

That part about B2 receptor antagonism causing vasodilation and bronchodilation seems totally wrong, and I was willing to write it off as a publishing error, however on the same card it lists bronchoconstriction as a side effect, so that got me thinking that maybe there's some kind of reflex vasodilation that I can't think of. Any thoughts on what's correct?

According to Lipittcott Illustrated Pharmocology 3rd (2006) edition, propanolol causes BOTH bronchoconstriction and reflex peripheral vasoconstriction. Hence, propanolol must never be used in treating patients with COPD. Hope it helps.

 

[Rogue_Leader]

According to Lipittcott Illustrated Pharmocology 3rd (2006) edition, propanolol causes BOTH bronchoconstriction and reflex peripheral vasoconstriction. Hence, propanolol must never be used in treating patients with COPD. Hope it helps.

That's what I thought. I have the Lippincott book too, so I did see that propranolol would peripheral vasoconstriction and bronchoconstriction. I just wanted to make sure that the Lange pharmcard was blatently wrong in the B2 blockade would increase (not decrease) vascular and bronchiolar smooth muscle constriction, and there wasn't some subtle reflex that I was missing.

 

[seasurfer]

That's what I thought. I have the Lippincott book too, so I did see that propranolol would peripheral vasoconstriction and bronchoconstriction. I just wanted to make sure that the Lange pharmcard was blatently wrong in the B2 blockade would increase (not decrease) vascular and bronchiolar smooth muscle constriction, and there wasn't some subtle reflex that I was missing.

I think those cards could be wrong, well sometimes, I even came across mistakes in books like BRS pathology, Trevor and Katzung pharmacology...etc. So I believe it could be mistake. You have to make a decision what you want to believe. If the questions in USMLE is asking "What is the adverse effect of propranolol?" After reading all the posts here, what will you answer?

 

[JulianCrane]

Wouldn't the decreased CO cause a sympathetic baroreceptor reflex with peripheral vasoconstriction through A1 receptors?

I see what you saying, but wouldn't that defeat the purpose of using a beta blocker as an anti-hypertensive?

 

[tupac_don]

I got Lange's Pharmacology cards and was flipping through the cards and I got to the Propranolol card. This is what is says under the mechanism of action

"Propranolol is a B1 and B2 receptor antagonist. By blocking the B1 receptor, HR and contractility are decreased, thereby leading to decreased cardiac output. By blocking the B2 receptor, vascular and respiratory smooth muscle constriction is decreased, which results in peripheral vasodilation as well as bronchodilation."

That part about B2 receptor antagonism causing vasodilation and bronchodilation seems totally wrong, and I was willing to write it off as a publishing error, however on the same card it lists bronchoconstriction as a side effect, so that got me thinking that maybe there's some kind of reflex vasodilation that I can't think of. Any thoughts on what's correct?

Its a typo for sure. Believe you me beta blockers are antagonists not agonists. I would go with bronchoconstriction.

 

[uacharya]

I got Lange's Pharmacology cards and was flipping through the cards and I got to the Propranolol card. This is what is says under the mechanism of action

"Propranolol is a B1 and B2 receptor antagonist. By blocking the B1 receptor, HR and contractility are decreased, thereby leading to decreased cardiac output. By blocking the B2 receptor, vascular and respiratory smooth muscle constriction is decreased, which results in peripheral vasodilation as well as bronchodilation."

That part about B2 receptor antagonism causing vasodilation and bronchodilation seems totally wrong, and I was willing to write it off as a publishing error, however on the same card it lists bronchoconstriction as a side effect, so that got me thinking that maybe there's some kind of reflex vasodilation that I can't think of. Any thoughts on what's correct?

Yeah, there's definately some type of a typo. Propanalol is a nonselective beta blocker and as a result would cause a decrease a cardiac output (B1 blockade) and cause vasoconstriction (B2 blockade of smooth muscle which will cause increased activity of MLCK); this is why it is contraindicated in asthma patients. Due to its side effect of bronchoconstriction.

B1 --> Increase cAMP --> Protien Kinase A --> L-type Ca++ channels Release Ca++ --> Contraction
B2 --> Increased cAMP --> Inhibition of MLCK --> Muscle Relaxation

So it would make sense if you nonselectively blockade both B-receptors, you are going to cause a decreased Cardiac Output but might increase your Systemic Vascular Resistance.

 

[tupac_don]

Yeah, there's definately some type of a typo. Propanalol is a nonselective beta blocker and as a result would cause a decrease a cardiac output (B1 blockade) and cause vasoconstriction (B2 blockade of smooth muscle which will cause increased activity of MLCK); this is why it is contraindicated in asthma patients. Due to its side effect of bronchoconstriction.

B1 --> Increase cAMP --> Protien Kinase A --> L-type Ca++ channels Release Ca++ --> Contraction
B2 --> Increased cAMP --> Inhibition of MLCK --> Muscle Relaxation

So it would make sense if you nonselectively blockade both B-receptors, you are going to cause a decreased Cardiac Output but might increase your Systemic Vascular Resistance.

Being a pharmacist I can safely tell you that it is a typo and that it doesn't have bronchodialating effect, its a typo.