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Pharmacology & Medical Chemistry II > Exam 2: Lecture X, Histamines > Flashcards

Exam 2: Lecture X, Histamines Flashcards

1
Q

Histamine and serotonin are synthesized from…..

A

amino acids

also antacids

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2
Q

Histamine made from…

A

histidine

stored in high conc in mast cells

Important in pathophysiological reactions (inflammation)
Released in response to IGE-mediated (immediate) allergy

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3
Q

Histamine in mast cells….

A

bound form is biologically inactive, stored in granules in mast/basophils

stimuli can trigger release

mast cells numbers at sites of potential tissue injury

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4
Q

Non-mast cell Histamine….

A

found in several tissues and brain

function as NT in brain…sleep + arousal, thermal/body weight regulation, neuroendocrine control and cardiovascular regulation

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5
Q

Ergot Alkaloids Toxicity Brain

A

Hallucinations resembling psychosis are common with the LSD

Methysergide is occasionally used as a “recreational drug” (an LSD substitute)

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6
Q

Ergot Alkaloids Toxicity Uterus

A

Powerful contractions may be produced during pregnancy
Uterus is progressively more sensitive to ergot alkaloids
Abortions are rare, however better to avoid ergot alkaloids
Avoid migraine treatment with ergot alkaloids during pregnancy

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7
Q

Ergot Alkaloids Toxicity Blood Vessels

A

Strong and prolonged vasoconstriction

An overdose may cause severe ischemia and gangrene

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8
Q

Release of Histamine (immunologic)

A

Immunologic response the important mechanism of mast cell/basophil histamine release

Cells sensitized by IgE attached antibodies degranulate explosively exposed to antigen

Degranulation leads to the release of histamine,ATP, and other stored mediators

Histamine released by this mechanism is a mediator in immediate (type I) allergic reaction

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9
Q

Chemical and Mechanical Release of Histamine

A

Drugs (morphineand tubocurarine) can displace bound histamine from the cells

Loss of granules from the mast cell also releases histamine

Chemical/Mechanical mast cell injury causes degranulation and histamine release

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10
Q

Histamine Effects

A

Flushing
Hypotension
Tachycardia
Bronchoconstriction

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11
Q

H1

A

Tissue:Smooth muscles, endothelium, brain

Signal Transduction:Gq; ↑IP3, DAG

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12
Q

H2

A

Tissue:Stomach, heart, mast cells, brain

Signal Transduction:Gs; ↑cAMP

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13
Q

H3

A

Tissue:Nerve endings, CNS, plexuses

Signal Transduction:Gi; ↓cAMP

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14
Q

H4

A

Tissue:Eosinophils, neutrophils, CD4 T-cells

Signal Transduction:Gi; ↓cAMP

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15
Q

H1 effects

A

Important in processes caused by IgE-mediated allergic responses
Typical responses – bronchoconstriction, and vasodilation
Vasodilation occurs due to release of NO
Capillary endothelium permeability increases with edema formation

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16
Q

H2 effects

A

Mediates gastric acid secretion by parietal cells
Cardiac stimulant effect.
By a negative feedback reduces histamine release from mast cells

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17
Q

H3 effects

A

Operates in presynaptic neurons in the CNS

Modulation of histamine neurotransmission in the CNS

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18
Q

H4 effects:

A

Operates in chronic inflammatory conditions

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19
Q

H1 antagonists:

A

Histamine solo = no therapeutic application

Histamine aerosol used as provocative test of bronchial hyperactivity

drug that block histamine effect = v important

Competitive antagonists at the H1 receptor in the periphery

Do not affect the release of histamine from storage sites

H1 antagonists resemble muscarinic antagonists and alpha-adrenergic blockers

H1 antagonists are pharmacological antagonists at muscarinic receptors and alpha-receptors

H1 antagonists may block serotonin receptors

H1 antagonists are characterized by extensive liver metabolism

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20
Q

1st vs 2nd Gen H1 antagonists

A

1st = strong sedative effects
more likely to block autonomic receptors

2nd = less sedating
h1 blockers less distributed into CNS

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21
Q

H1 antagonist Typical Effects

A 
Sedation
Antinausea and antiemetic effect
Antiparkinsonism effects
Anticholinoceptors effects
Antiadrenoreceptor effects
Antiserotonin effects
Local anesthesia
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22
Q

1st gen antihistamines

A

Ethanolamines: Carbinoxamine (Clistin), Diphenhydramine (Benadryl)

Piperazine derivatives: Hydroxyzine (Atarax), Meclizine (Bonine)

Alkylamines: Brompheniramine (Dimetane), Chlorpheniramine (Chlor-Trimeton )

Phenothiazine derivatives: Promethazine (Phenergan)

Miscellaneous agents: Cyproheptadine (Periactin)

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23
Q

2nd gen antihistamines

A

Piperidine: Fexofenadine (Allegra)

Miscellaneous agents: Loratadine (Claritin), Cetirizine (Zyrtec)

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24
Q

Diphenhydramine (Benadryl)

A

Treatment of Allergic reactions:
H1 receptors blockers are used for allergic conditions
Hay fever, urticaria, drug-sensitivity rashes, insect bite and stings
Agents are not effective in asthma.

CNS effects: Sedation, motion sickness, nausea, and vomiting

Anesthetic effect: Many H1 blockers are potent local anesthetics

25
Diphenhydramine (Benadryl) Toxicity
Toxicity: Common Highly sedative (diphenhydramine and promethazine) Antimuscarinic effect: Dry mouth and blurred vision Alpha-blocking effect: Orthostatic hypotension Less common toxicity: Excitation and convulsion in children Allergic responses (topical application of H1 antagonists)
26
H2 antagonists
Selectively block H2 receptors Structurally do not resemble H1 blockers No effect upon H1 receptors, 5-HT receptors, or α-receptors Active orally Relatively non-toxic Possible to use in large doses (single dose for 12-24 hours)
27
H2 antagonists Clinical Uses
Reduction of gastric acid secretion Acid-peptic disease - especially duodenal ulcer Effective in healing and preventing recurrences in gastric peptic ulcer Effective in acid hypersecretion, GI bleedings, and diarrhea Acute ulcer is treated with 2 doses/day Accelerate healing Prevent recurrences Recurrence can often be prevented with 1 single bedtime dose Very useful agents!
28
H2 prototype antagonist
Cimetidine (Tagamet) Relatively selective and have no effect upon H1 receptors Relatively non-toxic - can be given in large doses Main application in acid-peptic disease - especially duodenal ulcer Accelerates healing and prevents recurrences Recurrences may be prevented by a single bedtime dose Also effective in healing and preventing severe gastric peptic ulcers Very helpful in controlling acid hypersecretion Very helpful in treatment of GI bleeding and diarrhea May be used to treat gastroesophageal efflux disease (GERD)
29
Cimetidine (Tagamet) Toxicity
Relatively non-toxic Potent inhibitor of hepatic enzymes May reduces hepatic blood flow Antiandrogen effect in many patients (Newer H2 blockers do not have endocrine effects) ** Alcohol: Very serious drug interaction may occur
30
Serotonin Syndorme
skeletal muscle contraction precipitated when MAO inhibitors are given together with SSRI antidepressants. Two mechanisms are discussed – hyperthermia caused by muscle contraction, or by the effect of drugs upon the CNS
31
Serotonin is produced from amino acid....
tryptophan potent pain stimulant
32
Ondansetron (Zofran, Zuplenz)
5-HT3 blocker | Prevention of nausea and vomiting caused by chemotherapy and radiotherapy
33
Cyproheptadine (Periactin)
5-HT2 blocker and H1 blocker | Treatment of allergy symptoms – sneezing, watery eyes, and itching
34
Ketanserin ( Sufrexal )
5-HT2 and alpha adrenoreceptor blocker | An antihypertensive agent, and a scientific tool to study 5-HT2 receptors
35
Dexfenfluramine (Redux)
serotonin uptake inhibitor Inhibits the reuptake carrier for 5-HT Characterized by a pronounced and effective appetite-reducing effect Toxicity: Related to serious cardiac disease in patients – was withdrawn (2010)
36
Sumatriptan (Imitrex)
5-HT1d and 5-HT1B agonist. Effective in the treatment of acute migraine and cluster headaches Available for oral, nasal, and parenteral administration
37
5-HT3 Distribution
CNS sensory system. Chemoreceptors, vomiting center, | and enteric system
38
5-HT2 Distribution
CNS excitation system, smooth muscles, gut, bronchi, | uterus, vessels, and platelets
39
5-HT1d Distribution
Brain
40
5-HT6,7 Mechanism
Gs, increase cAMP
41
5-HT2 Mechnism
Gq, increase IP3/DAG
42
All other 5-HT receptors mechanism....
Gi, decrease cAMP
43
5-HT3 Mechanism
Gated channels, resembles Ach at nicotinic channels
44
Ergot Alkaloids
Ergot alkaloids are complex molecules Produced by a fungus in wet or spoiled grain Fungus also synthetize histamine, Ach, and tyramine Were responsible for the epidemics of “St. Anthony’s Fire” These epidemics were frequent during the Middle Ages
45
Ergot Alkaloids Receptors
Partial agonists at alpha-adrenoreceptors and 5-HT receptors Some ergot alkaloids are strong agonists at dopamine receptors
46
Ergot Alkaloids Classification base on....
organ or tissue involved
47
Bromocriptine (Parlodel, Barlolin, Brocriptin, and Butin )
for Parkinsonism extremely effective in reducing the high levels of prolactin from pituitary tumors associated with regression of the tumor, in some cases
48
Ergotamine used to treat....
acute migraine
49
Methysergide (Deseril) used for.....
migraine prophylaxis....not frequently prescribed
50
Ergot Alkaloid effect on blood vessel
OD can cause ischemia and gangrene Strong/prolonged a receptor mediated vasoconstriction
51
Migraine treatment
Ergot derivatives are highly specific for migraine pain Preferred by clinicians and patients Ergotamine tartrate for oral, sublingual, rectal, and inhaler use Often combined with caffeine  Vasoconstriction is long-lasting and cumulative Patient: careful with the oral preparation (10 mg per week) Ergotamine tartrate may be given intravenously or intramuscularly
52
Ergot Alkaloid effect on Brain
Hallucinations – more prominent with naturally occurring substances and LSD Hallucinations – less prominent with therapeutic agents
53
Ergot Alkaloid effect on Uterus
Powerful contraction near term Early in pregnancy high doses may cause abortion or miscarriage Useful contraction after placenta delivery (postpartum bleeding) Postpartum contractions reduce blood loss * **Ergonovine (Ergotrate) * *** Ergotamine
54
Preferred agent for control of postpartum hemorrhage.....
Oxytocin
55
Ergonovine use....
only for control for postpartum uterine bleeding should never be given before delivery
56
Vasoselective Ergot
Ergotamine used: Migraine/cluster headache Duration: 12–24 h Toxicity: Prolonged vasospasm causing angina, gangrene; uterine spasm
57
Uteroselective Ergot
Ergonovine Used: postpartum bleeding/migraine headache Duration: 2-4 h Toxicity: Prolonged vasospasm causing angina, gangrene; uterine spasm
58
CNS selective Ergot
LSD uses: none Duration: hours Toxicity: prolonged psychotic state/flashbacks

Pharmacology & Medical Chemistry II (43 decks)

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