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Pharmacology > 14) Histamine 5HT Ergot Alkaloids > Flashcards

14) Histamine 5HT Ergot Alkaloids Flashcards

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1
Q

Histamine synthesis and storage

A
  • Synthesized from istidine

- Stored in mast cells (enterochromaffin cells in the gut)

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2
Q

Histamine is metabolized by

A
  • Monoamine oxidase (MAO)

- Diamine oxidase

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3
Q

Excess production of histamine in the body (eg, in systemic mastocytosis) can be detected by

A
  • Measurement of its major metabolite (imidazole acetic acid) in the urine
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4
Q

Hitamine is released from mast cells in response to

A
  • IgE-mediated (immediate) allergic reactions

- Plays a pathophysiologic role in seasonal rhinitis (hay fever), urticaria, and angioneurotic edema

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5
Q

Histamine also plays a physiologic role in the control of

A
  • Acid secretion in the stomach

- As a neurotransmitter

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6
Q

Two receptors for histamine

A
  • H1 and H2
  • Mediate most of the peripheral actions
  • 2 others (H3, H4) have also been identified
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7
Q

The triple response

A
  • Demonstration of histamine effect on the skin
  • Mediated mainly by H1 and H2 receptors
  • This response involves a small red spot, an edematous wheal, which is surrounded by a red flare
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8
Q

H1 receptor distribution

A
  • Smooth muscle
  • Endothelium
  • Brain
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9
Q

H2 receptor distribution

A
  • Stomach
  • Heart
  • Mast cells
  • Brain
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10
Q

H3 receptor distribution

A
  • Nerve endings

- CNS

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11
Q

H4 receptor distribution

A
  • Leukocytes

- CD4 T-cells

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12
Q

5-HT1D/1B receptor distribution

A
  • Brain
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13
Q

5-HT2 receptor distribution

A
  • Smooth muscle
  • Platelets
  • Brain
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14
Q

5-HT3 receptor distribution

A
  • CNS

- Sensory and enteric nerves

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15
Q

5-HT4 receptor distribution

A
  • Gastro-intestinal tract
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16
Q

H1 and 5-HT2 post-receptor mechanisms

A
  • Gq; ↑ IP3 and DAG
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17
Q

H2 and 5-HT4 post-receptor mechanisms

A
  • Gs; ↑cAMP
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18
Q

H3, H4, and 5-HT1D/1B post-receptor mechanisms

A
  • Gi; ↓cAMP
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19
Q

5-HT3 post-receptor mechanism

A
  • Ligand-gated Na+/K+ channel
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20
Q

First generation H1 antagonists (blockers)

A
  • Very sedating
  • New subgroup prototyped by chlorpheniramine and cyclizine is less sedating
  • Half lives = 4–12 h
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21
Q

Second generation H1 antagonists (blockers)

A
  • Prototyped by loratadine
  • Great reduced sedation and autonomic effects
  • Half lives = 12–24 h
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22
Q

H1 blockers MOA

A
  • Competitive antagonists at the H1 receptor
  • No effect on histamine release from storage sites
  • More effective if given before histamine release occurs
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23
Q

Some (but not all) first-generation agents have

A
  • Anti-motion sickness effects (diphenhydramine, dimenhydrinate, cyclizine, meclizine….)
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24
Q

First generation H1 antagonists selectivity

A
  • Less selectivity to histamine receptors

- Anti-cholinergic activity

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25
Second generation H1 antagonists selectivity
- More selective to the peripheral histamine receptors | - Don’t cross the blood brain barrier (BBB) so they have less sedation side effects and less anticholinergic effects
26
H2 blocker prototype
- Dimetidine | - Single dose DOA may be 12–24 h
27
H2 antagonist (cimetidine) MOA
- Pharmacologic blockade of histamine H2 receptors - Relatively selective - No significant blocking actions at H1 or autonomic receptors
28
The only therapeutic effect of clinical importance (H2 receptor antagonist)
- Reduction of gastric acid secretion
29
Cimetidine
- Potent inhibitor of hepatic drug-metabolizing enzymes - May also reduce hepatic blood flow - Significant antiandrogen effects in patients receiving high doses (others don’t have this side effect)
30
H2 blockers (names)
- Ranitidine - Famotidine - Nizatidine - Cimetidine
31
Serotonin production/storage
- Produced from tryptophan | - Stored in vesicles in cells of the gut and neurons of the CNS and enteric nervous system
32
After release, serotonin is metabolized by
- Monoamine oxidase (MAO)
33
Excess serotonin production in the body can be detected by
- Measuring its major metabolite in the urine | - 5-hydroxyindole acetic acid (5-HIAA)
34
After release from neurons, serotonin
- Partially taken back up into the nerve ending by a serotonin reuptake transporter (SERT)
35
Serotonin agonists in clinical use act at these receptors
- 5-HT1D/1B - 5-HT2 - 5-HT4
36
Antidepressants
- Selective serotonin reuptake inhibitors (SSRI)
37
H1 receptor clinical outcome
- Itching - Pain - Bronchoconstriction - Vasodilation, local edema
38
H2 receptor clinical outcome
- Gastric acid secretions
39
H3 receptor clinical outcome
- Appetite suppressant investigation
40
5-HT2 receptor clinical outcome
- In the CNS, mediate a reduction in appetite that has been used in the treatment of obesity
41
5-HT3 receptor clinical outcome
- Sspecially in the chemoreceptive area and vomiting center | - Antagonists have anti-emetic effects
42
5-HT4 receptor clinical outcome
- Intestinal motility
43
Prototypic H1 antagonists
- Diphenhydramine | - Loratadine
44
Prototypic H3 antagonists
- Clobenpropit
45
Prototypic H4 antagonists
- Thioperamide
46
Prototypic 5-HT1D/1B agonists
- Triptans: Sumatriptan,….
47
5-HT2 prototypic agonists
- Loracserin
48
5-HT2 prototypic antagonists
- Ketanserin
49
5-HT3 prototypic antagonists
- Ondansetron
50
5-HT4 prototypic agonists
- Tegaserod (partial agonist)
51
5-HT4 prototypic antagonists
- Tegaserod (partial agonist)
52
5-HT1D/1B agonists (names)
- Sumatriptan - Almotriptan - Eletriptan - Frovatriptan - Naratriptan - Rizatriptan - Zolmitriptan
53
5-HT1D/1B agonists indication
- Acute migraine | - Cluster headache
54
5-HT1D/1B agonists side effects
- Paresthesias - Pain - Dizziness - Coronary vasospasm
55
5-HT2 agonists indication
- Treatment of obesity
56
5-HT3 agonists indication
- Especially in the chemoreceptive area and vomiting center | - Antagonists have anti-emetic effects
57
5-HT4 agonists indication
- Chronic constipation
58
5-HT4 agonists side effects
- Cardiovascular toxicity
59
5-HT2 antagonist names/MOA
- Ketanserin, cyproheptadine are competitive antagonists | - Phenoxybenzamine is an irreversible blocker
60
5-HT2 antagonist indication
- Treatment of carcinoid tumor (neoplasm that secretes large amounts of serotonin and peptides) - Causes diarrhea, bronchoconstriction, and flushing
61
5-HT2 antagonist side effects
- Ketanserin, phenoxybenzamine: cause α-blockade thus have α-blockade SE - Cyproheptadine: causes H1-blockade thus has H1-blockade SE
62
5-HT3 antagonists (names)
- Ondansetron - Granisetron - Dolasetron - Alosetron
63
5-HT3 antiemetic actions
- Vomiting associated with cancer chemotherapy and postoperative vomiting
64
Alosetron (5-HT3 antagonist) is used in the treatment of
- Women with irritable bowel syndrome associated with diarrhea
65
5-HT3 antagonist side effects
- Diarrhea | - Headache
66
Dolasetron (5-HT3 antagonist) side effects
- Has been associated with QRS and QTc prolongation in the ECG
67
Alosetron (5-HT3 antagonist) side effects
- Causes significant constipation | associated with fatal bowel complications
68
Serotonin and drugs with 5-HT agonist effects are associated with
- Hyperthermia (high fever) - Hyperreflexia and tremors (skeletal muscle effects) - Cardiovascular abnormalities (hypertension) - Hyperactive bowel syndrome; diarrhea - Mydriasis - Agitation and coma that can be life-threatening
69
Precipitating drugs
- SSRI - Sumatriptan - Ondansetron - Not sure how and if true
70
Mild Serotonin Syndrome symptoms
- Mydriasis - Shivering - Sweating - Tachycardia (mild)
71
Moderate Serotonin Syndrome symptoms
- Altered mental status - Autonomic hyperactivity - Neuromuscular abnormalities
72
Life threatening Serotonin Syndrome symptoms
- Delirium - Hypertension - Hyperthermia - Muscle rigidity - Tachycardia
73
Ergot alkaloid clinical effects on vessels
- Migraine treatment - α-adrenoceptor–mediated vasoconstriction - Overdose can cause ischemia and gangrene of the limbs or bowel
74
Ergot alkaloid clinical effects on uterus
- Reduce post-partum bleeding - Powerful and long-lasting contraction that reduces bleeding - Contract the uterus especially near term (delivery) - Ergonovine is the prototype - In pregnancy, the uterine contraction is sufficient to cause abortion or miscarriage
75
Ergot alkaloid clinical effects on the brain
- Bromocriptine has been used to reduce prolactin secretion (dopamine is the physiologic prolactin release inhibitor) in Hyperprolactinemia and parkinsonism
76
Hallucinations may be prominent with
- Naturally occurring ergots - Lysergic acid diethylamide (LSD) - Uncommon with the therapeutic ergot derivatives
77
In the pituitary, some ergot alkaloids are
- Potent dopamine-like agonists and inhibit prolactin secretion - Bromocriptine are among the most potent semisynthetic ergot derivatives

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