Ouli Maty
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What the difference between Epi and NE in the heart?
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| mapetrsn
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Beta-2 receptors bind Epi tighter than NE and show give a greater response
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| mjl1717
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At low doses epi stimulates B receptors and at high does it stimulates alpha receptors
Epi has a positive chronotropic affect, CO increases, positive inotropic affect, The cummulative affect at the peripheral receptors causes an increase in systolic B.P. and decrease in diastolic B.P. (In reference to the SA node the slope of phase 4 is increased)
NE-In general when given in therapeutic doses to humans the alpha receptor is most affected. Causes intense peripheral vasoconstriction.
Systolic and diastolic BP increase. In isolated cardiac tissue NE stimulates contractility;however in vivo little cardiac stimulation is noted. This is due to NE inducing a reflex increase in vagal activity by enhancement of baroreceptors This bradycardia is sufficient to counteract local actions of NE on the heart
If there is pretreatment with atropine (which blocks vagal effects) NE produces tachycardia.
Good q.
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| Ouli Maty
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Very clear Doc. Thank you.
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| medmanparadise
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Pulse pressure and HR is also a great way to look at the differences.
Epinephrine:
Due to the increase in inotropy to the heart per greater more dominant B effects, the systolic pressure increases greatly; concurrently because the a receptors are not stimulated to the same degree, the diastolic takes a resultant dip leaving creating a widening of the pulse pressure. Note that for the most part the mean bp stays the same thru out.
Norepinephrine:
As the a receptors are the dominant receptors to be stimulated (with b2 being very minor) the resultant vascular smooth muscle contraction -> increased TPR = increased bp (both systolic and diastolically. The B1 are not signifacntly stimulated thus there is a compensatory vagal response - reflex bradycardia - which overcomes the postive chronotropic effects.
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