Pharmacology · Adrenergic Pharmacology
Classification, signal transduction cascades, tissue distribution, and regulation
Abbreviations: IP3 = inositol trisphosphate · cAMP = cyclic AMP · JG = juxtaglomerular · ICU = intensive care unit · D1 = dopamine D1 receptor · GRK = G-protein-coupled receptor kinase
Receptor Subtypes & G-Protein Coupling
Alpha-1
Gq → IP3 / Calcium
Alpha-2
Gi → Decreased cAMP
Beta-1
Gs → Increased cAMP
Beta-2
Gs → Increased cAMP
Beta-3
Gs → Restricted Distribution
Dopamine — Dose-Dependent Receptor Engagement
| Dose Range | Receptor Engaged | Clinical Effect |
|---|---|---|
| Low (~1–3 mcg/kg/min) | D1 | Renal and mesenteric vasodilation; natriuresis. Does not protect against acute kidney injury (ANZICS trial). |
| Moderate (~3–10 mcg/kg/min) | Beta-1 | Increased cardiac output; positive inotropy and chronotropy |
| High (>10 mcg/kg/min) | Alpha-1 | Systemic vasoconstriction; profile resembles norepinephrine; arrhythmia risk increases |
Receptor Regulation — Three Clinical Scenarios
Beta-2 Agonist Tachyphylaxis
Chronic albuterol overuse → beta-2 receptor downregulation → reduced bronchodilation. Fix: inhaled corticosteroids as controller; short-acting agonist for rescue only.
Beta-Blocker Withdrawal
Chronic blockade → beta-1 upregulation → abrupt stop → rebound tachycardia / angina / myocardial infarction risk. Always taper over 1–2 weeks.
Heart Failure Remodeling
Chronic norepinephrine excess → beta-1 downregulation → impaired contractile reserve. Beta-blockers (carvedilol, metoprolol succinate) reverse this over months.
Suggested References
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|---|---|---|
| Katzung BG (ed) | Basic and Clinical Pharmacology, 15th ed. Chapter 9: Adrenoceptor-Activating and Other Sympathomimetic Drugs | McGraw-Hill, 2021 |
| Brunton LL, Knollmann BC (eds) | Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed. Chapter 9: Adrenergic Agonists and Antagonists | McGraw-Hill, 2023 |
| Lefkowitz RJ | Seven transmembrane receptors: something old, something new | Acta Physiol (Oxf). 2007;190(1):9–19 |
| Ahlquist RP | A study of the adrenotropic receptors | Am J Physiol. 1948;153(3):586–600 |
| Bylund DB, Eikenberg DC, Hieble JP, et al | International Union of Pharmacology nomenclature of adrenoceptors | Pharmacol Rev. 1994;46(2):121–136 |
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| Missale C, Nash SR, Robinson SW, et al | Dopamine receptors: from structure to function | Physiol Rev. 1998;78(1):189–225 |
| Bellomo R, Chapman M, Finfer S, et al; ANZICS Clinical Trials Group | Low-dose dopamine in patients with early renal dysfunction: a placebo-controlled randomised trial | Lancet. 2000;356(9248):2139–2143 |
| Tonini M, Cipollina L, Poluzzi E, et al | Clinical implications of enteric and central D2 receptor blockade by antidopaminergic gastrointestinal prokinetics | Aliment Pharmacol Ther. 2004;19(4):379–390 |
| De Backer D, Biston P, Devriendt J, et al | Comparison of dopamine and norepinephrine in the treatment of shock | N Engl J Med. 2010;362(9):779–789 |
| Krupnick JG, Benovic JL | The role of receptor kinases and arrestins in G protein-coupled receptor regulation | Annu Rev Pharmacol Toxicol. 1998;38:289–319 |
| Bangalore S, Makani H, Radford M, et al | Clinical outcomes with beta-blockers for myocardial infarction: a meta-analysis of randomized trials | Am J Med. 2014;127(10):939–953 |