Histamine & Serotonin (Exam IV) Flashcards
What two types of pruritis exist?
Differentiate the two.
- Neurogenic = Suppressed pain response or noxious stimuli.
- Psychogenic = Imagined. (think of your nose being itchy so it then becomes itchy)
What are mediators of pruritis called?
What are the main members of this “group”
Autacoid Groups.
1. Histamine
2. Serotonin
3. Leukotrienes
4. Prostaglandins
What are histamines derived from?
Histadine (amino acid)
Where are the three main places where histamine is found?
- Mast cells (Immune system “vesicles”)
- Brain (as a neurotransmitter)
- Stomach (to create acid)
What are the two ways that histamine is released?
- Chemical Response
- Morphine and Tubocurarine - Mechanical Response
- Mast Cell damage (particularly crush injuries)
Which two drugs cause an itchiness response by displacing histamine from mast cells?
Morphine and Tubocurarine
How many histamine receptor subtypes are there? (that we need to know about)
H1 - H4
Where are H1 receptors found?
Brain, smooth muscle, endothelium
Where are H2 receptors found?
Gastric Mucosa
Where are H3 receptors found?
Brain
Where are H4 receptors found?
WBC’s
What two ways exist to antagonize histamine?
- Physiologic reversal of effects with epinephrine.
- Histamine receptor antagonists.
Do 2nd generation H1-Antagonists cross the BBB?
What is the consequence of this?
No, less sedation is observed.
Do first generation H1-Antagonists cross the BBB?
What does this result in?
What is a drug example?
- Yes
- Sedation
- Benadryl (diphenhydramine)
Which four first generation H1-antagonists should be known?
What is their respective use/effect?
- Dimenhydrinate (dramamine) - motion sickness
- Diphenhydramine (benadryl) - sedation
- Promethazine (phenergan) - antiemetic
- Cyproheptadine (periactin) - antiserotonin
What 2nd generation H1-antagonists should be known?
- Fexofenadine
- Loratadine
- Cetirizine
What is an off-label use for H1-antagonists?
Pregnancy morning sickness
What would H1-antagonist toxicity symptoms be?
- Sedation
- Antimuscarinic effects (urinary retention & blurred vision)
- Paradoxical (excitations, convulsions, paradoxical hypotension)
What are H2-antagonists used for?
What is their mechanism?
- Decreasing stomach acid
- Blocking histamine from binding to H2 receptors in the parietal cells of the stomach.
How is stomach acid made?
- Histamine binds to H2 receptors in stomach parietal cells
- H2 receptors = ↑ cAMP = PKA
- PKA = ↑ proton pumps = HCl acid.
What drug class is generally more effective for stomach acid reduction than H2-antagonists?
PPI
Where is 90% of serotonin?
- GI tract
Where does serotonin target (produced?) in the GI tract?
What would cancer in this location cause?
- Enterochromaffin cells
- Diarrhea
Where does serotonin target (produced?) in the vasculature?
Platelets (constricts blood vessel at side of bleed where platelets are)
Where is serotonin produced in the brain?
What does it regulate in the brain?
- Raphe Nuclei
- Essentially everything
What is the precursor molecule of serotonin?
What type of molecule is this?
L-Tryptophan (an amino acid)
What drug class can precipitate serotonin syndrome?
MAOI’s
What enzyme metabolizes serotonin?
What is serotonin metabolized into?
How is this metabolite important?
- Monoamine oxidase (MAO)
- 5-hydroxindoleacetic acid (5-HIAA)
- 5-HIAA is detectable in blood to test for enterochromaffin tumors.