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THE PHARMACOLOGY OF ADRENERGIC RECEPTORS. M.T. Piascik PHA 824 December 11 & 16, 2008. Learning Objectives. The student should be able to explain or describe; The pharmacodynamic principles that aid in the understanding of adrenergic receptors and the actions of drugs on these receptors.

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THE PHARMACOLOGY OF ADRENERGIC RECEPTORS

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The pharmacology of adrenergic receptors l.jpg

THE PHARMACOLOGY OF ADRENERGIC RECEPTORS

M.T. Piascik

PHA 824

December 11 & 16, 2008


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Learning Objectives

The student should be able to explain or describe;

The pharmacodynamic principles that aid in the understanding of adrenergic receptors and the actions of drugs on these receptors.

The criteria upon which alpha and beta receptors are defined.

The second messenger systems utilized by alpha and beta receptors and how activation of these receptors leads to a change in physiologic function.


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Learning Objectives(cont.)

The student should be able to explain or describe;

The effects of alpha and beta receptor activation on the heart and blood vessels.

The effects of isoproterenol, epinephrine and norepinephrine on the cardiovascular system.

The clinical uses and potential toxicities of epinephrine, norepinephrine and isoproterenol with emphasis on epinephrine.


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The Adrenergic Receptors


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Beta Adrenergic Receptors

DRUGKD BETA1 RECEPTORKD BETA2 RECEPTOR

Epinephrine800 nM800 nM

Norepinephrine1000 nM10,000 nM

Isoproterenol80 nM80 nM


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Which of the dose-response curves represents activation of the beta1 receptor and which represents activation of the beta2 receptor?


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Beta Adrenergic Receptor Systems

TissueReceptor Subtype

Heartbeta1

Adipose tissuebeta1

Vascular smooth musclebeta2

Airway smooth musclebeta2

Kidney-renin release from JG cellsbeta1


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Cellular Signaling Activated by the Beta1 Receptor in the Heart


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Rhythm disturbances are a major concern with drugs that activate the beta1 receptor.

Physiologic Consequences of Beta1 Receptor Activation


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The BETA1-Adrenergic Receptor as a Therapeutic Target

  • Agonists- congestive heart failure

    2) Antagonists- hypertension, ischemic heart disease, congestive heart failure, supraventricular tachyarrhythmias.


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Cellular Signaling Activated by the Beta2 Receptor in Smooth Muscle


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Physiologic Consequences of Beta2 Receptor Activation


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The Beta2-Adrenergic Receptor as a Therapeutic Target

Agonists- Airways dysfunction (asthma, chronic bronchitis emphysema), tocolytics

Antagonists- No therapeutic uses.


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The BETA2-Adrenergic Receptor as a Therapeutic Target

  • Agonists- congestive heart failure

    2) Antagonists- hypertension, ischemic heart disease, congestive heart failure, supraventricular tachyarrhythmias.


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Alpha Adrenergic Receptors

KD KDKD

BETA1 RECEPTOR BETA1 RECEPTORALPHA RECEPTOR

Epinephrine800 nM800 nM5000 nM

Norepinephrine 1000 nM10,000 nM* 6000 nM

Isoproterenol 80 nM80 nM 10,000 nM**

* At doses used in therapeutics, Norepinephrine is void of Beta2 activity

** At doses used in therapeutics, Isoproterenol is void of Alpha1 activity


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Presynaptic Alpha2 Receptors


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Postsynaptic Alpha1 Receptors


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Physiologic Consequences of Alpha1 Receptor Activation


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Interaction Between Vascular Alpha1 and Beta2 Receptors


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Integrated Cardiovascular Responses


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Integrated Cardiovascular Response to Isoproterenol and Norepinephrine


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Integrated Cardiovascular Response to Epinephrine


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Therapeutic Uses of Epinephrine

Oral dosing of epinephrine, norepinephrine or isoproterenol is not possible due to its rapid metabolism in the gut by MAO.

Epinephrine can be given topically, by injection (s.c., i.m. i.v) or inhalation


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Therapeutic Uses of Epinephrine(cont.)

Actions at the Beta2 Receptor

  • The treatment of respiratory distress or bronchspasm caused for example by asthma (i.e. status asthmaticus) or anaphylaxis as a result of allergic responses.

    Actions at the Beta1 Receptor

  • Epinephrine is also used to provide rapid inotropic support in cardiopulmonary resuscitation


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Therapeutic Uses of Epinephrine(cont.)

Actions at the Beta2 Receptor

  • The treatment of respiratory distress or bronchspasm caused for example by asthma (i.e. status asthmaticus) or anaphylaxis as a result of allergic responses.

    Actions at the Beta1 Receptor

  • Epinephrine is also used to provide rapid inotropic support in cardiopulmonary resuscitation


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Therapeutic Uses of Epinephrine(cont.)

Actions at the Alpha1 Receptor

  • Epinephrine is often used in combination with local anesthetic agents (such as articaine, bupivacaine or lidocaine) to prolong the duration of anesthetic action.

  • Epinephrine is used in

    surgery to reduce bleed.


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Epinephrine Toxicities

  • Arrhythmias

  • Hypertension

  • Toxicity can occur following systemic administration or systemic absorption following oral administration.


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Epinephrine Toxicities

  • Arrhythmias

  • Hypertension

  • Toxicity can occur following systemic administration or systemic absorption following oral administration.


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Epinephrine Toxicities

  • Toxicity can be potentiated in patients taking tricyclic antidepressants, nonselective beta blockers, cocaine and amphetamine-like drugs and those under general anesthesia.


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Beta1-AR

Beta2-AR


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