Caffeine?

[AVPU]

I didn't know where else to post this, so I apologize upfront if it's better suited for another forum. I had a question in class the other day (I teach CPR and FA) re: caffeine intake. It was a basic question, but it got me thinking:

is caffeine a vasodilator or constrictor?

I've done all sorts of research online, and am getting both answers. I'm inclined to think it's a vasodilator, relaxes things, BP goes down, HR increases.

While we're on it, how about alcohol??

Thanks guys!!

 

[bstone]

I'm tempted to say constrictor.

 

[AVPU]

Thanks for the quick reply? Can u say why??

 

[bstone]

I think I saw it on House. In reality, caffeine is a stimulant. Stimulants constrict things and elevate pressures.

 

[Lifeguards For Life]

I didn't know where else to post this, so I apologize upfront if it's better suited for another forum. I had a question in class the other day (I teach CPR and FA) re: caffeine intake. It was a basic question, but it got me thinking:

is caffeine a vasodilator or constrictor?

I've done all sorts of research online, and am getting both answers. I'm inclined to think it's a vasodilator, relaxes things, BP goes down, HR increases.

While we're on it, how about alcohol??

Thanks guys!!

Caffeine is the prototype drug for the methylxanthines, and as such would be a vasoconstrictor. Methylzanthines as a class are very similar too amphetamines.

Alcohol is generally classified as a depressant and is a vasodilator at lower doses, but at higher doses it acts as a vasoconstrictor.

 

[Lifeguards For Life]

Thanks for the quick reply? Can u say why??

While the exact mechanism of action of methylxanthines is not clear, we think it blocks adenosine(a2) receptors. Adenosine is an endogneous neurotransitter, used clinically to treat certain tachycardias.


The way it relates to your question, basically, adenosine is created in the brain and binds to a2 receptors. The binding of adenosine causes drowsiness by slowing down nerve cell activity. In the brain, adenosine binding also causes blood vessels to dilate.

To a nerve cell, caffeine looks like adenosine. Caffeine therefore binds to the a2 receptor. However, it doesn't slow down the cell's activity like adenosine would. As a result, the cell can no longer identify adenosine because caffeine is taking up all the receptors that adenosine would normally bind to. Instead of slowing down because of the adenosine's effect, the nerve cells speed up. Caffeine also causes the brain's blood vessels to constrict, because it blocks adenosine's ability to open them up.

attached is a link with more detail.
http://www.cellscience.com/Reviews5/caffeine_adenosine_receptor.html

 

[bstone]

While I don't disagree with the above statements, I firmly believe it is the gnomes that pinch the blood vessles closed when one drinks caffeine.

 

[Lifeguards For Life]

While I don't disagree with the above statements, I firmly believe it is the gnomes that pinch the blood vessles closed when one drinks caffeine.

That is actually what i meant by a2 receptor.

 

[bstone]

That is actually what i meant by a2 receptor.

Oh good. I thought you were going to say something silly like fairies! Everyone knows fairies don't exist!

 

[Smash]

Interestingly enough antagonism of adenosine receptors is the way that cocaine exerts it's effect, which may go some way to explaining why it nearly killed me when I went from 12 espressos a day to 2.

Methylxanthines also include theophylline; caffeine I believe is sometimes used in NICU with prem babies to assist their breathing - stimulates breathing and heart rate due to the stimulant effect.

Or I might have made that all up. It's hard to tell sometimes.

 

[Lifeguards For Life]

Methylxanthines also include theophylline; caffeine I believe is sometimes used in NICU with prem babies to assist their breathing - stimulates breathing and heart rate due to the stimulant effect.

Or I might have made that all up. It's hard to tell sometimes.

No, I remember reading about that in our textbook. Theophylline's relax smooth muscles and are sometimes useful in treating asthma

 

[VentMedic]

No, I remember reading about that in our textbook. Theophylline's relax smooth muscles and are sometimes useful in treating asthma

There is a reason your grandmother made you drink hot black tea when you had some wheezey congestion.

 

[medic417]

There is a reason your grandmother made you drink hot black tea when you had some wheezey congestion.

And why you have to drop coffee if taking theophylline so you don't overdose.

 

[TransportJockey]

I always remember it's a constrictor because it helps with H/A and a lot of hte OTC migraine meds have it in it.

 

[AVPU]

Thanks for the great responses. So it seems there is a lot of incorrect statements out there, stating that caffeine is a dilator.

I have just one more question. If caffeine constricts, increasing pressure, wouldn't it lower HR? Don't the two always have an inverse relationship? Or is it b/c its a stimulant that it artificially raises BP AND HR??

 

[TransportJockey]

My thought on that is cause it's a stimulant it causes HR to rise. Probably also why you can get some arythmias from too much caffeine.

 

[mycrofft]

You're thinking and asking questions. Good.

When HR increases because of lowered BP, that is a different pathway than the actions of stimulants. Baroreceptors and other mechanisms act to increase pump pressure (chronotropic, or rate, mostly, but also inotropic, or strength, especially when adrenaline or epinephrine is involved).

That is also why you suspect toxin or chemicals when an expected physiologic picture looks daffy; something is in there screwing with receptors, cell membranes, etc.

OK...theobromine? GO!

PS: Roger the arrythmias, my being case in point. I also have an exaggerated cariovascular response to epinephrine, including that in local anesthetics.

 

[TransportJockey]

When HR increases because of lowered BP, that is a different pathway than the actions of stimulants. Baroreceptors and other mechanisms act to increase pump pressure (chronotropic, or rate, mostly, but also inotropic, or strength, especially when adrenaline or epinephrine is involved).

That is also why you suspect toxin or chemicals when an expected physiologic picture looks daffy; something is in there screwing with receptors, cell membranes, etc.

OK...theobromine? GO!

PS: Roger the arrythmias, my being case in point. I also have an exaggerated cariovascular response to epinephrine, including that in local anesthetics.

Similar to the extremely tachy and HTN in some cocaine overdoses? It might be an extreme example... OR they are HTN because their HR shot through the roof... I'm gonna go do some reading now and try and look it up. I can't remember off the top of my head right now

 

[Smash]

OK...theobromine? GO!

My other vice...

 

[mycrofft]

Hi, I'm Mycrofft, I'm a Chocoholic

hint hint