Overview of Receptors and Drugs By Kevin Mikielski, D.O. Department of Cardiology

Receptors and Actions

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

Specific Drugs EPINEPHRINE Stimulates Alpha 1 Stimulates Beta 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 Norepinephrine Stimulates Alpha 1 Stimulates Beta 1 In general, this is its major site of action and its major clinical use Stimulates Beta 1 Stimulates Beta 2

Dopamine 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

Dopamine (continued) 5-10 mcg/kg/min 10-20 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 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 / Vasopressin 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 / Atropine Adenosine Atropine 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 Increases sinus rate and AV nodal conduction Does not directly increase blood pressure

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