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Introduction
1. Anatomy
2. Microbiology
3. Physiology
4. Pathology
5. Pharmacology
5.1 Pharmacokinetics
5.2 Pharmacodynamics
5.3 Receptors, agonists and antagonists
5.4 Types of drug receptors
5.5 Anti-neoplastic drugs
5.6 Adverse effects of chemotherapeutic drugs
5.7 Newer chemotherapeutic drugs
5.8 Important drugs of the cardiovascular system
5.9 Antimicrobials
5.10 Drugs acting on the renal system
5.11 Drugs acting on the respiratory system
5.12 Drugs acting on the gastrointestinal system
5.13 Antidiabetics and insulin
5.14 Miscellaneous
5.15 Additional information
6. Immunology
7. Biochemistry
8. Cell and molecular biology
9. Biostatistics and epidemiology
10. Genetics
11. Behavioral science
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5.3 Receptors, agonists and antagonists
Achievable USMLE/1
5. Pharmacology

Receptors, agonists and antagonists

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Receptors and drugs acting as agonists and antagonists

Receptor Agonist Antagonist
Alpha 1 (dilator pupillae, vascular smooth muscle) Dopamine; Phenylephrine Prazosin; Doxazosin
Alpha 2 (CNS, presynaptic nerve terminals) Clonidine Yohimbine
Beta 1 (heart, CNS) Dopamine; Dobutamine Atenolol; Metoprolol; Propranolol
Beta 2 (islet cells of pancreas, smooth muscle in bronchioles, blood vessels and uterus) Salbutamol; Terbutaline
Beta 3 Mirabegron
Alpha and beta Epinephrine; Norepinephrine (alpha > beta; causes reflex bradycardia) Labetalol
Alpha Phentolamine (reversible); Phenoxybenzamine (irreversible)
Beta 1 and beta 2 Dopamine; Isoprenaline Propranolol; Oxprenolol
Angiotensin or AT 1 and AT 2 Angiotensin Candesartan (most potent blocker of AT1 receptor); Losartan; Telmisartan; Irbesartan; Valsartan
Muscarinic Acetylcholine; Carbachol; Bethanechol Atropine and analogues; Homatropine; Pirenzepine (M1); Trihexyphenidyl; Tricyclic antidepressants; Quinidine; Disopyramide
Nicotinic Acetylcholine; Carbachol Ganglion blockers; Neuromuscular blockers; Aminoglycoside antibiotics; Quinidine
Dopamine Apomorphine; Bromocriptine; Dopamine Butyrophenones, haloperidol; Domperidone (D2); Metoclopramide; Phenothiazines, chlorpromazine
GABA -A Benzodiazepines; GABA Bicuculline
GABA -B GABA Baclofen
Histamine H1 Histamine Antihistamines like cetirizine, promethazine
Histamine H2 Histamine Cimetidine; Ranitidine; Famotidine
5 hydroxytryptamine or 5 HT 5HT Methysergide; Sumatriptan (5HT 1D); Ondansetron (5HT 3)
Leukotriene or LT Leukotrienes Montelukast; Zafirlukast
Opioid receptors (μ, δ, and κ) Morphine; Endorphins; Enkephalins; Pentazocine (μ); Buprenorphine (κ) (partial agonist); Fentanyl, alfentanil, remifentanil; Oxycodone; Methadone; Codeine; Papaverine Naltrexone (μ, δ, and κ); Methylnaltrexone (δ); Nalorphine (μ); Naloxone (δ and κ); Buprenorphine (κ) (partial agonist)
Vasopressin V1 and V2 Vasopressin (ADH) Conivaptan (V1 and V2); Nelivaptan (V1); Tolvaptan (V2)

Beta blockers and receptor selectivity

  • Beta 1 selective are acebutolol, atenolol, metoprolol, esmolol
  • Nonselective (beta 1=beta 2) are propranolol, timolol, nadolol
  • Nonselective (both alpha and beta) = labetalol, carvedilol

Alpha Receptors

  • Alpha 1 agonists: dopamine, phenylephrine; antagonists: prazosin, doxazosin
  • Alpha 2 agonist: clonidine; antagonist: yohimbine
  • Nonselective alpha antagonists: phentolamine (reversible), phenoxybenzamine (irreversible)

Beta Receptors

  • Beta 1 agonists: dopamine, dobutamine; antagonists: atenolol, metoprolol, propranolol
  • Beta 2 agonists: salbutamol, terbutaline
  • Beta 3 agonist: mirabegron
  • Beta 1 and 2 agonists: dopamine, isoprenaline; antagonists: propranolol, oxprenolol

Combined Alpha and Beta Receptors

  • Agonists: epinephrine, norepinephrine (alpha > beta, causes reflex bradycardia)
  • Antagonist: labetalol

Angiotensin Receptors (AT1, AT2)

  • Agonist: angiotensin
  • Antagonists: candesartan (most potent AT1 blocker), losartan, telmisartan, irbesartan, valsartan

Muscarinic and Nicotinic Receptors

  • Muscarinic agonists: acetylcholine, carbachol, bethanechol; antagonists: atropine, homatropine, pirenzepine (M1), trihexyphenidyl, tricyclic antidepressants, quinidine, disopyramide
  • Nicotinic agonists: acetylcholine, carbachol; antagonists: ganglion blockers, neuromuscular blockers, aminoglycosides, quinidine

Dopamine Receptors

  • Agonists: apomorphine, bromocriptine, dopamine
  • Antagonists: butyrophenones, haloperidol, domperidone (D2), metoclopramide, phenothiazines, chlorpromazine

GABA Receptors

  • GABA-A agonists: benzodiazepines, GABA; antagonist: bicuculline
  • GABA-B agonist: GABA; antagonist: baclofen

Histamine Receptors

  • H1 agonist: histamine; antagonists: cetirizine, promethazine
  • H2 agonist: histamine; antagonists: cimetidine, ranitidine, famotidine

Serotonin (5 HT) Receptors

  • Agonist: 5HT
  • Antagonists: methysergide, sumatriptan (5HT 1D), ondansetron (5HT 3)

Leukotriene Receptors

  • Agonist: leukotrienes
  • Antagonists: montelukast, zafirlukast

Opioid Receptors (μ, δ, κ)

  • Agonists: morphine, endorphins, enkephalins, pentazocine (μ), buprenorphine (κ, partial), fentanyl, oxycodone, methadone, codeine, papaverine
  • Antagonists: naltrexone (μ, δ, κ), methylnaltrexone (δ), nalorphine (μ), naloxone (δ, κ), buprenorphine (κ, partial)

Vasopressin Receptors (V1, V2)

  • Agonist: vasopressin (ADH)
  • Antagonists: conivaptan (V1, V2), nelivaptan (V1), tolvaptan (V2)

Beta Blockers and Receptor Selectivity

  • Beta 1 selective: acebutolol, atenolol, metoprolol, esmolol
  • Nonselective (beta 1 = beta 2): propranolol, timolol, nadolol
  • Nonselective (alpha and beta): labetalol, carvedilol
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Receptors, agonists and antagonists

Receptors and drugs acting as agonists and antagonists

Receptor Agonist Antagonist
Alpha 1 (dilator pupillae, vascular smooth muscle) Dopamine; Phenylephrine Prazosin; Doxazosin
Alpha 2 (CNS, presynaptic nerve terminals) Clonidine Yohimbine
Beta 1 (heart, CNS) Dopamine; Dobutamine Atenolol; Metoprolol; Propranolol
Beta 2 (islet cells of pancreas, smooth muscle in bronchioles, blood vessels and uterus) Salbutamol; Terbutaline
Beta 3 Mirabegron
Alpha and beta Epinephrine; Norepinephrine (alpha > beta; causes reflex bradycardia) Labetalol
Alpha Phentolamine (reversible); Phenoxybenzamine (irreversible)
Beta 1 and beta 2 Dopamine; Isoprenaline Propranolol; Oxprenolol
Angiotensin or AT 1 and AT 2 Angiotensin Candesartan (most potent blocker of AT1 receptor); Losartan; Telmisartan; Irbesartan; Valsartan
Muscarinic Acetylcholine; Carbachol; Bethanechol Atropine and analogues; Homatropine; Pirenzepine (M1); Trihexyphenidyl; Tricyclic antidepressants; Quinidine; Disopyramide
Nicotinic Acetylcholine; Carbachol Ganglion blockers; Neuromuscular blockers; Aminoglycoside antibiotics; Quinidine
Dopamine Apomorphine; Bromocriptine; Dopamine Butyrophenones, haloperidol; Domperidone (D2); Metoclopramide; Phenothiazines, chlorpromazine
GABA -A Benzodiazepines; GABA Bicuculline
GABA -B GABA Baclofen
Histamine H1 Histamine Antihistamines like cetirizine, promethazine
Histamine H2 Histamine Cimetidine; Ranitidine; Famotidine
5 hydroxytryptamine or 5 HT 5HT Methysergide; Sumatriptan (5HT 1D); Ondansetron (5HT 3)
Leukotriene or LT Leukotrienes Montelukast; Zafirlukast
Opioid receptors (μ, δ, and κ) Morphine; Endorphins; Enkephalins; Pentazocine (μ); Buprenorphine (κ) (partial agonist); Fentanyl, alfentanil, remifentanil; Oxycodone; Methadone; Codeine; Papaverine Naltrexone (μ, δ, and κ); Methylnaltrexone (δ); Nalorphine (μ); Naloxone (δ and κ); Buprenorphine (κ) (partial agonist)
Vasopressin V1 and V2 Vasopressin (ADH) Conivaptan (V1 and V2); Nelivaptan (V1); Tolvaptan (V2)

Beta blockers and receptor selectivity

  • Beta 1 selective are acebutolol, atenolol, metoprolol, esmolol
  • Nonselective (beta 1=beta 2) are propranolol, timolol, nadolol
  • Nonselective (both alpha and beta) = labetalol, carvedilol
Key points

Alpha Receptors

  • Alpha 1 agonists: dopamine, phenylephrine; antagonists: prazosin, doxazosin
  • Alpha 2 agonist: clonidine; antagonist: yohimbine
  • Nonselective alpha antagonists: phentolamine (reversible), phenoxybenzamine (irreversible)

Beta Receptors

  • Beta 1 agonists: dopamine, dobutamine; antagonists: atenolol, metoprolol, propranolol
  • Beta 2 agonists: salbutamol, terbutaline
  • Beta 3 agonist: mirabegron
  • Beta 1 and 2 agonists: dopamine, isoprenaline; antagonists: propranolol, oxprenolol

Combined Alpha and Beta Receptors

  • Agonists: epinephrine, norepinephrine (alpha > beta, causes reflex bradycardia)
  • Antagonist: labetalol

Angiotensin Receptors (AT1, AT2)

  • Agonist: angiotensin
  • Antagonists: candesartan (most potent AT1 blocker), losartan, telmisartan, irbesartan, valsartan

Muscarinic and Nicotinic Receptors

  • Muscarinic agonists: acetylcholine, carbachol, bethanechol; antagonists: atropine, homatropine, pirenzepine (M1), trihexyphenidyl, tricyclic antidepressants, quinidine, disopyramide
  • Nicotinic agonists: acetylcholine, carbachol; antagonists: ganglion blockers, neuromuscular blockers, aminoglycosides, quinidine

Dopamine Receptors

  • Agonists: apomorphine, bromocriptine, dopamine
  • Antagonists: butyrophenones, haloperidol, domperidone (D2), metoclopramide, phenothiazines, chlorpromazine

GABA Receptors

  • GABA-A agonists: benzodiazepines, GABA; antagonist: bicuculline
  • GABA-B agonist: GABA; antagonist: baclofen

Histamine Receptors

  • H1 agonist: histamine; antagonists: cetirizine, promethazine
  • H2 agonist: histamine; antagonists: cimetidine, ranitidine, famotidine

Serotonin (5 HT) Receptors

  • Agonist: 5HT
  • Antagonists: methysergide, sumatriptan (5HT 1D), ondansetron (5HT 3)

Leukotriene Receptors

  • Agonist: leukotrienes
  • Antagonists: montelukast, zafirlukast

Opioid Receptors (μ, δ, κ)

  • Agonists: morphine, endorphins, enkephalins, pentazocine (μ), buprenorphine (κ, partial), fentanyl, oxycodone, methadone, codeine, papaverine
  • Antagonists: naltrexone (μ, δ, κ), methylnaltrexone (δ), nalorphine (μ), naloxone (δ, κ), buprenorphine (κ, partial)

Vasopressin Receptors (V1, V2)

  • Agonist: vasopressin (ADH)
  • Antagonists: conivaptan (V1, V2), nelivaptan (V1), tolvaptan (V2)

Beta Blockers and Receptor Selectivity

  • Beta 1 selective: acebutolol, atenolol, metoprolol, esmolol
  • Nonselective (beta 1 = beta 2): propranolol, timolol, nadolol
  • Nonselective (alpha and beta): labetalol, carvedilol