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Adrenergic Receptor Agonists

59-291 Section 2, Lecture 4. Adrenergic Receptor Agonists. Termed sympathomimetic drugs Divided into three groups Direct-acting agonists Catecholamines Noncatecholamines Indirect-acting agonists Mixed acting agonists. Catecholamines. Naturally occurring:

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Adrenergic Receptor Agonists

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  1. 59-291 Section 2, Lecture 4 Adrenergic Receptor Agonists • Termed sympathomimetic drugs • Divided into three groups • Direct-acting agonists • Catecholamines • Noncatecholamines • Indirect-acting agonists • Mixed acting agonists

  2. Catecholamines • Naturally occurring: • NE: endogenous sympathetic neurotransmitter • EP: The principle hormone of adrenal medulla • Dopamine: Precursor to EP and NE • Synthetic: Isoproterenol, dobutamine • Structure: catechol moiety, ethylamine side chain • Inactivation: COMT, MAO; found in the gut, liver and other tissues • Low oral bioavailability, short plasma half-lives • Must be administered parenterally for systemic actions; Anaphylactic shock

  3. Mechanisms and Effects • Cathecolamines differ in their affinities and specificities for receptors • Size of alkyl substitution on the amine nitrogen determines the relative affinity for a and b receptors • Larger alkyl group, higher affinity for b- receptors; Isoproterenol

  4. Ethylamine NE: Constricts all blood vessels EP: Constricts some blood vessels but dilates the others Dopamine: stimulates release of NE from sympathetic nerves (Direct and indirect agonist)

  5. Sys, Dias., MeanArt. P

  6. Adverse effects: -excessive vasoconstriction leading to ischemia -reduces blood flow to vital organs such as kidneys; cause excessive cardiac stimulation leading to myocardial ischemia or arrythmias --adrenergic agonists: hyperglycemia undesirable in diabetics Indirect-Acting Amphetamine- induces the release of NE Cocaine-prevents reuptake of NE

  7. Mixed-Acting: the name says it all! Direct and Indirect acting adrenergic agonists activate both α and  receptors Ephedrine and Pseudoephedrine vasoconstriction via 1 receptors; useful as nasal decongestants; via  bronchodilate Adverse effects: tachycardia, hypertension, urinary retention

  8. Practice Questions • Which of the following drugs does stimulate mainly b receptors • NE • EP • Isoproterenol • Dopamine

  9. Which of the following catecolamines may cause reflex bradycardia due to stimulation of a1 receptors? • NE • EP • Dopamine • Isoproterenol

  10. What is the treatment of choice for anaphylactic shock • NE • EP • Isoproterenol • Dobutamine

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