By Kevin Mikielski, D.O.
Department of Cardiology

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Alpha 1
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Present on peripheral vasculature
Stimulation results in vasoconstriction
Beta 1
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Present in myocardium and conduction system
Stimulation results in enhanced contractility, heart rate and speed on conduction in electrical system of heart
Beta 2
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Present in skeletal muscle, lung and vasculature
Stimulation results in vasodilatation and bronchodilatation

 EPINEPHRINE
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Stimulates Alpha 1
 Vasoconstriction
Stimulates Beta 1
 Increases contractility, heart rate and conduction
 Overall effect is to increase cardiac output
Stimulates Beta 2
 Vasodilates
 Bronchodilates
Will increase cardiac output through Beta 1; Usually will increase blood pressure due to Alpha 1>Beta 2

 Norepinephrine
 Stimulates Alpha 1
 In general, this is its major site of action and its major clinical use
 Stimulates Beta 1
 Stimulates Beta 2

 Dopamine
 Actions are dose-dependent but wide variation/range of effects are seen
 1-5 mcg/kg/min
 Stimulates dopamine receptors
 Increased renal blood flow
 Has NEVER been shown to have clinical benefit and “Renal dose dopamine” should not be used

 5-10 mcg/kg/min
 Primarily stimulates Beta 1 receptors
 10-20 mcg/kg/min
 Primarily stimulates Alpha 1 receptors
 Great amount of overlap between doses and effects

 Dobutamine
 Stimulates Beta 1 and 2 receptors
 Not a good drug for hypotension unless the etiology is severe LV dysfunction, acute MI with cardiogenic shock, or acute pulmonary embolism where hypotension will improve with increased cardiac output
 Usually will decrease blood pressure due to Beta 2 effects

 Phenylephrine (Neosynephrine)
 Stimulates Alpha 1 receptors
 No Beta effect
 Vasopressin (ADH)
 Stimulates V1 receptors and acts similar to Alpha 1 agonists, but exact mechanisms of vasoconstriction are not completely understood
 Cautious use in patients with ACS and CHF because it can result in coronary spasm and volume retention

 Adenosine
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Acts via Adenosine 1 receptor in conduction system to slow heart rate/SA/AV block
Need to give rapidly as bolus followed by flush due to ½ life of only 6 seconds
 Atropine
 Acts to inhibit AcH effects on conduction system
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Increases sinus rate and AV nodal conduction
Does not directly increase blood pressure

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