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Author Topic: heart rate  (Read 4823 times)

Offline qazibasit

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heart rate
« on: 01/07/2004 17:31:52 »
3,5-cAMP produced in the heart by the effectors (adenylate cyclase) of adrenergic receptors is inhibited to 5-AMP by a reaction with phosphodiesterase this also occurs by caffine and theophylline which are chemically methylxanthines and are present in tea and coffee so what will their effect be on heart rate witll the heart rate increase or decrease.
« Last Edit: 01/07/2004 17:34:31 by qazibasit »


 

Offline DrN

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Re: heart rate
« Reply #1 on: 03/07/2004 20:11:09 »
whoa! slow down and use some punctuation!

i think you're trying to ask if tea and coffee increase heart rate? well, yes, caffeine is known to stimulate heart rate.
 

Offline qazibasit

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Re: heart rate
« Reply #2 on: 04/07/2004 00:07:08 »
Thanks for that, now I will try to learn some punctuation.
 

Offline chris

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Re: heart rate
« Reply #3 on: 05/07/2004 01:41:17 »
The heart is innervated by the sympathetic nervous system which uses the neurotransmitter nor-adrenaline (NA) which acts (predominantly) at beta-1 receptors. These are cardio-acceleratory (positively chronotropic - they increase heart rate) and positively inotropic (they increase contractility or the force or heart contraction). The same receptors are also targeted by circulating adrenaline released by the adrenal glands.

As you say, the receptors are linked (via G proteins) to adenylate cyclase, the enzyme which makes a second messenger called cAMP (cyclic adenosine monophosphate) which regulates intracellular calcium and various other processes. The more NA or adrenaline, the more cAMP produced in the target cells.

The cAMP signal is halted by the action of a second enzyme called phosphodiesterase which breaks down cAMP. Phosphodiesterase is inhibited by a class of agents called methyl xanthines, of which caffeine is an example.

If you block the action of phosphodiesterase you stop cAMP being broken down and hence you potentiate (increase) the effect of noradrenaline and adrenaline.

That's why strong coffee increases your heart rate, boosts arousal and, in sufficient doses, makes you shaky and panicky. You are mimicking an adrenaline rush, even though your adrenaline levels are normal or low.

Chris

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The Naked Scientists Forum

Re: heart rate
« Reply #3 on: 05/07/2004 01:41:17 »

 

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